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Document:	DECnet Digital Network Architecture Phase IV NSP Functional Specification
Order Number:	AA-X439A-TK
Revision:	0
Pages:	160
Original Filename:

OCR Text

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DECnet Digital Network Architecture

NSP Functional Speclflcatlon

Order No. AA-X439A-TK

December 1983

This document describes the NSP architecture, which models that part
of the DECnet software that supports the creation and destruction of

logical links, error control, and flow control. NSP is the protocol
of the
End Communications layer. The End Communications layer is part of the
Digital Network Architecture.

SU_PERSESSION/UPDATE INFORMATION: This is a new manual.
VERSION:

4.0.0

To ‘orde_r additional copies of this document, contact your local
Digital Equipment Corporation Sales Office.

digital equipment corporation - maynard, massachusetts

First Printing, ”December 1983

The information in this document is subject to change without notice and should not be construed as a
commitment by Digital Equipment Corporation. Digital Equipment Corporation assumes no responsibility
for any errors that may appear in this document.

The software describedin this documentis furnished under a license and may only be used or copiedin

accordance with the terms of such license.

No responsibilityis assumed for the use or rehablhty of software on equipment thatis not supplied by

DIGITAL or its afflhated companies.

The postage-prepaid READER’S COMMENTS form on the last page of this document requests the user’s
critical evaluation to assist us in preparing future documentation.

The following are trademarks of Digital Equipment Corporation:

DIGITAL
DEC

DECsystem-10
|

DECtape

MASSBUS

OMNIBUS

PDP

DIBOL

DECUS

EDUSYSTEM

COMPUTER LABS

FOCAL

RSX

COMTEX

INDAC

TYPESET-8

DDT

LAB-8

TYPESET-11

DECCOMM

DECSYSTEM-20

TMS-11

UNIBUS

ASSIST-11

0S/8

PHA

FLIP CHIP

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DATATRIEVE

TRAX

ITPS-10

SBI
~

PDT

Distributed Systems Publications typeset this manual using DIGITAL’s
TMS-11 Text Management System.

MGTPEALL

Page

Contents
CONTENTS

|
0
0

INTRODUCTION

FUNCTIONAL

2
3
4

4.1
.4.2
.1.3
.4.4

e«

Logical Links And Ports
.. «
Port And Logical Link States .
Logical Link Identification
.

«
.«
. .
. .

«
.
.

Data

FIow
.

.«

.
.

o =

.
.
.

Major NSP Functlons
.
'
.
Establishing And Destroylng Loglcal Llnks

e
.
. . . . . . .
User Messages
e e e
o o o o
.
oo
o o o
e+ o e
. ..
.

NSP

Link

o«

States

¢«
.
.

+«
.
.

«
.

e
e
o

e
o

Data

5
0

Buffer
DETAILED

Base

Pools . . .
FUNCTIONAL MODEL
Interface Routines . .

e
e

e
¢
o

e
e
s

e
o
o

s
e

.
.

.
.
e
o

o
o

Transmit Processes
.
Connect/Disconnect Transm1t Processes
.
Data Transmit Processes
. .« « « « o« « .
Reserved Transmit Processes
.

Transmit Allocation Module
~ ALGORITHMS . .
Data Segment

. . .
e e o
Retransm1551on

[]

.
.

e
.
.

.
.
o

o
.

Other-Data Handling
. .. . . .
Retransmission Timer Value Estima
Inactivity Timing
. . « « & o &

.
.

.
e

.
.

Transmit Format Module
Segmentation Module
.

("‘0

8
S
0
1
2
3

Reassembly Module

.6
.6.1
.6.2
6.3

.
.

[}

c
o
e
Receive Dispatcher Module
e e e e e e
Index to Routlnes
. . ¢ o « « « o o o o
Recelve Processes
. . .
e o o o e o
Connect/Disconnect RECEIVE Processes .
Data Receive Processes . . «« « + o o
Reserved Receive Processes c e e e .

)

]
.

DATA BASES AND BUFFER POOLS

Node

NSP's Internal Data Base . . «
Session Control Port Data Base
Reserved Port Data Base
. . .

1
2
3
.4
4.1
4.2
4.3

States

Logical
NSP

Port

Interface

STATES

.
.

Error Control
. . . .
.
Flow Control
« o
Normal Data Flow Control « o
Interrupt Data Flow Control
Segmentation And Reassembly Of
Functional Components
.
c
Data Bases And Buffer Pools
e
Modules
. . . . « ¢ ¢ ¢ ¢ ¢ ¢
NSP INTERFACES . . .
e e« o o
Session Control Interface
¢ o o
Network Management Interface . .

Routing

.
.

.6.2
0.3
.6.3.1
.6.3.2
.6.4
7
7.1
1.2
.0
.1
.

.1
.2
3

.6
.6.1

\.—o»’d

Messages

\“1

DESCRIPTION

Design Scope . .
¢« o o
Relation to DIGITAL Network Archltecture
Routing Characteristics
. ¢« « « o« o « o
Basic NSP Concepts « ¢ « « o« o« o« o o o o

Table

110
112

Interrupt MesSSage

.«

No Operation Message

113
115

o
.

o
«

o
o

o
«

o
o

o«

o
o

o«
o

«
o

& o
o o
. .
. .
« «
o o

o
o«
.
.
«
o

+ « « 121
o o«o 124
. . . 124
. . . 126
« « o« 127
o« « o 128

o«

««

Connect Initiate And Retransmitted Connect
Initiate MesSsSagesS
.« « o « o « o o « o « o
Connect Confirm Message
. « « « ¢ « « « «
Disconnect Initiate Message
. . . .. . .

Disconnect Confirm Message

o
o

o« 116
o 117

1189

128

o
o
.

129
131
133

>:T$’

N+

113

Link Service Message . . .« « o« o o
Acknowledgment TYPES ¢ « o« « o o o o
Data Acknowledgment Message
. . .
Other-Data Acknowledgment Message
Connect Acknowledgment Message . .
Control MeSSAgeS. « « o« 2 o o o o o

w N+

FORMATS

Message Format Notation
General Message Format
Data MesSSAgesS . + « « «
Data Segment MesSSage .

0N b= W

« «

o @

o«

¢«

B.2

DATA STRUCTURES

OPERATION

o .@

+ &« +

[]

« « o o « « o« o « « « « « « B-

[}

[ ] .. . [ J i

«
|J

o
L2

[]

o«

o
|J

® B

C.2

APPENDIX D

DATA STRUCTURES
OPERATION
[] LJ |J

&
v
LJ | ®

&
|]

TRANSMIT ALLOCATION MODULE

o
[]

.‘

o
LJ

.
L] ‘.

EXAMPLE

+ « v o v o o o o o o o o o o o .

DATA STRUCTURES

OPERATION

(]

[-]

APPENDIX E

REVISION HISTORY

APPENDIX

GLOSSARY

]

[]

q)fl

C.l

REASSEMBLY MODULE EXAMPLE

)

[}

[]

APPENDIX C

-0

STRUCTURES

INTERFACE TO THE ALGORITHM . +. v
DATA

SEGMENTATION MODULE EXAMPLE

B.1

134

CJEJU

112

Confidence Testing

i
i

W N

- APPENDIX B

whwlw

4
Page

Contents

LOGICAL LINK ADDRESS ASSIGNMENT/DEASSIGNMENT
-

APPENDIX A

MESSAGE

)

N AN WWWWN
QO

)

o 00 O

"ot
n

0O 00 00 OO0 00 00 OO 00 0 00 00 00 OO 0O

Table

Page 5

Introduction
INTRODUCTION

1.0

1interfaces,

functions,

structure,

the

This document describes

and

The
the protocol of the End Communications Layer.
messages of NSP,
Network
DIGITAL
the
of
part
that
1s
Layer
ns
Communicatio
End
Architecture (DNA) that models the software (or hardware) enabling the
flow
data
creation and destruction of logical communication 1links,
reassembly
and
segmentation
the
and
control,
error
end-to-end
control,
|

of messages.

DECnet
which
on
model
the
1is
DIGITAL Network Architecture
A DECnet network is a family of software
implementations are based.
modules, data bases, and hardware components used to tie DIGITAL

systems

together

resource

for

remote system communication.

a layered structure.
DNA is

functions.

Modules

different computer

within

dlstrlbuted computation or

sharing,

Modules in each

systems)

single

communicate

DNA

in
(but typically

layer

specific

wusing

distinct

perform

layer

protocols.

in the same computer
typically
(but
layers
in different
Modules
system) interface using subroutine calls or a system- dependent method.
in terms of calls to
interfaces are described
In this document
subroutines.

1II,
In Phase
This spec1f1cat10n describes Phase IV NSP architecture.
With Phase III
an earlier version, Session Control was part of NSP.
from NSP,
and Phase IV, Session Control has been logically separated

The Session Control

and the 1nterface between the two layers defined.

The
Layer is described in a separate functional specification.
Routing specification, also a part of the Phase II NSP spec1f1cat10n
has been greatly expanded in Phase III and Phase IV and 1is contained
Appendix E details the
separate Routing specification.
a
in

‘(\

)

differences between Phase III

and Phase IV NSP.

A glossary at the end of this document defines many NSP terms. This
is familiar with computer
reader
the
that
assumes
document
The primary audience consists of those who
communications and DECnet.
however, the document may be useful to
implement DECnet systems;
The other
anyone interested in the details of DECnet structure.
current DNA functlonal spec1f1cat10ns are:

DNA Data Access Protocol (DAP) Functional Specification, Version

DNA

Digital

Communications

Data

Protocol

Messagev

(DDCMP)

Functional Specification, Version 4.1.0, Order No. AA-K175A-TK

DNA Ethernet Data Link Functional
Order No.

AA-Y298A-TK

Maintenance

3.0.0,

Operations

Order No.

Functional

AA-X436A-TK

Version

Specification,

DNA Ethernet Node Product Architecture
1.0.0, Order No. AA-X2440A-TK
DNA

5.6.0, Order No. AA-K177A-TK

1.0.0,

Specification, Version
o
|
Specification,
|

Version

Introduction

DNA Network Management Functional
Order No.

Page
6

Specification,

Version

4.0.0,

2.0.0,

Order

AA-X437A-TK

DNA Routing Layer Functional
No. AA-X435A-TK
DNA Session Control
No. AA-K182A-TK

Specification,

Functional

Version

Specification,

Version

1.0.0,

Order

The Ethernet - A Local Area Network - Data Link Layer and Physical
Layer
Xerox),

DECnet

(Order

DIGITAL Network

No.

architecture
and
specifications.

2.0
NSP

Architecture

AA-N149A-TC)
an

provides

introduction

2.0,

(Digital,

(Phase

IV)

General

overview

each

the
‘

Intel,

and

Description

the

network

functional

FUNCTIONAL DESCRIPTION
performs

the

following

functions:

1. Enables
the creation

(logical

network

1links)

node

and

destruction

virtual

channels

that can be used for sending messages within

and between

Manages the
movement
transmit
buffers
to
mechanisms.

network

nodes.

of
interrupt
and
normal data
from
receive ‘buffers,
wusing
flow control

3. Breaks up normal data messages into portions (segments)

and
reassembles
after
they
have
:

these
been

Guarantees
the delivery of

control

data

and

specified destination by means of
Section

2 is

an overview of NSP,

covering

an
the

‘0

Design scope

Relation of NSP to the DIGITAL Network

Routing

Basic concepts(Section2.4)

error

messages

control mechanism.

following

topics:

(Section 2.1)

2.2)

characteristics

(Section

o) MeSsages (Section 2.5)
o

that

can
be
transmitted
1individually,
segments
1n
theilr
correct order
transmitted.

Major functions (Section 2.6)

Architecture

(Section

2.3)

The

Specifications,
Version
Order No. AA-K759B-TK

Design Scope

NSP satisfies these following design requirements:

Compatibility. NSP version 4.0 is compatible with previous
~versions of NSP except for those differences described 1n

Appendix E.

Performance.

NSP allows an implementation to perform without

Promptness.

d moving data
NSP minimizes the delays incurre1n

Efficiency. NSP minimizes the communications

Extensibility.

Fairness.

deadlocks while using dynamic buffer pools.

ov rnead

example, line bandwidth) consumed by the protocol.

the

established

a subset.
future, leaving earlier functions as

the

NSP accommodates additional functions in

If more than one logical link

1is

same destination at the same time, NSP assures that each

provides useful communication services.

from one Session Control module to another.

Page 7

Functional components (Section 2.7)

2.1

Functional Description

Elasticity.
resources

NSP allows an

(both

for performance.

trade

implementation

memory

algorithm complexity and buffer pool sizes)
-

The following are not within the scope of Phase IV NSP:

1.
-

Maximum throughput.

NSP will not

throughput of a logical link.

2. Uniform service.
throughput

NSP will not

necessarily
|

the

guarantee

maximize
same

the

average

and average delays over two logical links from a

common source to a common destination.

2.2

Relation to DIGITAL Network Architecture

Figure 1 shows the relationship of the End Communications Layer to the

DNA

hierarchy.

protocols.

Each layer in DNA consists of functional modules and
-

Generally, modules use the services of the next lowest layer. In this
document the service relationship 1is demonstrated in the way the

Note, however,
-- as calls to subroutines.
interfaces are modeled
each of the
with
that the Network Management Layer interfaces directly
interface
Control
Session
lower layers. Also, all the layers above

- Functional Description
directly
referred

with
to

1it,
the

|
In

fact,

"end user.”

the

|
three

upper

|
layers

are

Page 8

sometimes

4\“’/

Modules of the same type in the same layer communicate with each other
to provide their services.
The rules governing this communication and
the messages required
constitute
the
protocol
for
those
modules.
Messages
are
typically
exchanged
between
equivalent
modules
1in
different nodes.
However, equivalent modules within a single node can
also exchange messages.

———————

)

e ————= ! Network !
-

———————

Page 9

Functional Description

=
e e e =

Management

e ee

Modules

i ———— o —

e e ——————

!
!
\Y
\Y
!
!
!
.
e
!
!
r
!
| Network Application Modules
:----> !
o
b
e
- ] e
!
!
!
!
!
!
!
!
!
Vv
Vv
Vv
!
!
— e —————— o - . !
e
mm
e
!
!
R
Session Control Modules
¢ ———=>
f
vy

!
P
!
§—
v

———

!
!
!
!

!
\'/
TT )

!
!
!

!
\Y
—=.
————
e ———————
f—mm——mmmmmm
!
Modules
e —————— > | End Communications
e

——

—— e

——— —

{

!
!
!

TTT T

§ e ——————— > | Routing Layer Modules

!
!

—— e

—————— e

!
Vv

——

{—m————————— > | Data Link Modules
——_—_,—,,—————
Ne

!
Vv

!
Vv
!

e, ———_——————— '

!
\Y

!
!

o« T T ,—-——————-—' —————————— ®

R ittt > | Physical Link Modules

Figure 1.

NSP Relation to DNA

to
A brief description of each layer follows in order from the highest
|
the lowest layer:
l.

User Layer.

The highest layer, the User Layer supports

user

services and programs. Programs such as the Network Control
Program, which interfaces with the Network Management Layer,
and file transfer programs, which interface with the Network
Application Layer,

reside in the User Layer.

Functional Description

Page 10

Network Management Layer. The Network
Management
Layer
is
the only
one that has direct access to each lower layer for
control purposes.
Modules in this layer provide user control
over
and
access
to network parameters and counters. These
modules also perform up-line dumplng, down-1line loading,
and

|
3.

testing functions.
|
Network
Application
Layer.
Modules
in
the
Network
Application
Layer
support network functions, such as remote
file access and file transfer, used by the User
and
Network
Management

4.,

Layers.

Session Control

Layer.

The

Session

Control

defines

the

system-dependent aspects of logical link communication, which
allows messages to be sent from one
node
to
another
1in
a
networx.
Session
Control functions include name to address
translation,
process
addressing,
and,
1n
some
systems,
process activation
and access control.

End

Communications

defines
the
communication.

6.
7.

The

End Communications
aspects

1logical

Routing Layer.

Modules in the Routing Layer route

called packets,

between

source

and destination

Data Link Layer. The Data Link Layer
‘concerning data 1ntegr1ty and phy51cal

2.3

Layer.

system-independent

defines
channel

Layer
1link

messages,

nodes.
the
protocol
management

Physical Link Layer.
The Physical Link Layer
encompasses
a
part of the device driver for each communications device plus
the communications hardware itself,
The
hardware
includes
interface devices, modems, and the communication lines.

Reuting Characteristics

NSP interfaces directly with
the
Routing
Layer
for
1its
services.
Routing
1is a datagram delivery service to NSP.
A datagram is
a block
of data sent intact from one DECnet node to
another.
Routing
.sends
‘datagrams
1n
packets.
NSP
expects Routing
to have the following
characteristics:
|

,;l.

Routing w1ll accept a datagram at least as large as 230 8-bit
bytes.

There 1s an extremely low.probability that Routihg will:
a.

vDuplicate’a datagram

‘b,

Deliver a datagram to the wrong destination

- C.

Changelthe data in a datagram

Routing‘may fail to deliver a datagram.

N’

Functional Description
4,

Page 11

Routing may fail to deliver datagrams to a glven destination
from a given source 1in the order they were transmltted

from a given
5. Datagrams delivered to a given destlnatlon
a variable delay while under the control of
source undergo
Routing.
However, this maximum delay 1s bounded.
Datagrams
not delivered w1th1n the maximum delay will not be dellvered

2.4

Basic NSP Concepts

section

This

describes

understanding of NSP.

concepts that
|

are

fundamental

Ldgical links and porté (Section 2.4.1)

Port and logical link states (Section 2.4.2)

Logical link identification (Section 2.4.3)

Data flow (Section 2.4.4)

-) 2.4.1 Loglcal Llnks And Ports - NSP prov1des a logical 1link between
service

A logical link is a virtual connection
to Session Control.
two Session Control modules, either between two nodes or within one
The connection enables controlled communication between network
node.

nodes.
A pair of Session Control modules
may
have
more
than
one
Each logical 11nk is separate from all
them.
Dbetween
1link
logical
other

logical

links.

Each logical link must have a port at each end.
A port is an area
1in
memory, generally in a dedicated or shared pool, that contains control
in Section 5.2
4
Table
1links.
logical
for managing
variables

Each node on a network
NSP manages ports.
specifies these variables.
has a number of available ports.
In forming
-a logical link, one port
is

associated with another.

When Session Control requests a logical link or requests that
a port
be opened to receive an incoming connect request, NSP allocates a port
if sufficient resources are available.
When Session Control
requests

a port be closed, NSP deallocates the resources associated with
that
the port.
Deallocation usually occurs after Se551on Control
requests
a loglcal

link dlsconnectlon.

NSP also maintains a "confldence" variable in each port that has

opened.
useful

Session

Control

has

access

in detecting network failures.

been

to this information, which is
|

Functional Description

2.4.2

one

Page

Port And'ngical Link States - Each end of a logical link is in
a

set

of states

any

time.

“state.
The

1In

other

words,

each port

states

one

end of

the

link

affect

has

the

states

the

other

end

of
the link.
In this document the possible link states at one end of
a link are called the port states.
The logical link
states
are
the
combination of possible states at both ends of the logical link.

Evéry logical link has its own set of logical link states.
Session Control

requests

and NSP

messages

determine

the

particular

states
and
state transitions of the logical link.
NSP manages these
state changes, based
on
the
particular
requests
and
messages
it
receives.
Sectzon
5
details
all
the normal port and logical link
states and state transitions.
|
|

2.4.3
Logical Link Identification - In order for two NSP
modules
to
manage a given logical link, each NSP module must be able to identify
the link.
The
Iogical
1link
1identification
consists
of
the
port
addresses at each end of the link.
|
Each NSP module assigns a 16-bit numerical address to
1its
end of a
logical link.
The port at one end of the link contains the address
of
the port at the other end of the link and vice versa.
This is the way
in
which
the two ports are associated with each other.
The complete
identification of the link, identifying both
ends
of the
1link,
1is
therefore a 32-bit number.
|
|

To avold using the same number
module refrains from assigning

(but now disconnected)

to identify two different links, an NSP
a 16-bit address it used for a previous

link to a new link as

long

possible.

The

probability
that
each
of
the
two NSP modules reassigns its 16-bit
address and that these two addresses are paired a second time during a
connection
process is extremely low.
Therefore, the probability that
the same 32-bit identification would exist for two different links
1is
very
low.
This
ensures
that
there
will be no cross-talk between
links.
|

2.4.4

Data

Flow

After

logical

link

established,

data may

flow

in
both
directions
(full-duplex)
from transmitting Session Control
transmit buffers through the
network
+to
receiving
Session
Control
receive
buffers.
The size of the buffers at each end of the link is
implementation-dependent.
However,
the
data
flowing through
the
network 1is always handled the same way.
The NSP interface to Session
Control takes Session Control data provided in DATA-XMT calls (Section
3.1).
It
then
transforms the data to a network form.
At the other
end of the link the receiving NSP
interface,
responding
to
Session

Functional Description

‘Page 13

Control DATA-RCV calls, transforms the data from its network form to
are
The mechanisms NSP uses to handle data
its receive buffer form.
transparent to Session Control. From Session Control's viewpoint, the
data flow is as shown in Figure 2.

ed a transmitting
from
This figure shows Session Control data transform

Session Control to a transmitting NSP and then transformed back from a
not
The NSP data does
a receiving Session Control.
receiving NSP to
(The DNA General
actually move tarough the network as shown.
the
through
actually move
Description shows how Routing packets
network.)

Functional

Description

Page

Tfansmitting Node
| TRANSMITTING
|
SESSION CONTROL
|
|
| =
| | B |
| B |
11 u |
| u |
| I F |
| F |
| | F |
| 7 |
| | E |.
0 B
| | R |
I R |
I
B
I
| | # |
| # |
| | N |
[ 1|
|
===
——— e — e —

|
:

Interface

|
|
|
|
|
|
I
|
I
|
I

I
:
|
|=====,,
|
| |
I
| |
|
| |
I
| |
I
||
I
| |
|
| |
|
| |
|
| |

e eV

|
\
/
|
\/
|
######################
#
Bh4HeHHHH GRS HSHY
#
#

#
#

bH4H#t

|
HH##E

|
-

o E 3L
#
#

NETWORK

-e .

| E
| O
| M

|
|
|

|
DATA

I
|
I

|
|
|

E
O
M

|
|
|

DATA

|
|
|

#4444

8
————
'
HH##
#
|
#
#
#
#
#
HHHHAGHEE
RS
«
3T
EE:
|
N
I?###################

| |

Receiving Node

EOM

end-of-message

DATA

a collection
of 8-bit bytes

flag

I
|
|
I

{

I
I
I
|

I
I
|
|

RECEIVING
SESSION CONTROL
——-

THEme"
o

S I

NSP
Interface

— %

|
|
I
I

WS
w

| |
| |
| |
| ]

LEGEND:

#
#

Figure
2. Model of Data Flow as Seen by Session Control.

The transmitting NSP appends the end-of-message

Page 15

Functional Description

(EOM)

(Figure

flags

2), to the data in the network form. The receiving NSP module removes
these flags, places only data in the Session Control receive buffers,

informs the receiving
and then
returned receive buffer whether an
|

details this procedure.

Throughout the data flow
places data bytes from a
in the same order as they
no data will be
that
;

procedure.

2.5

Session Control via a flag in a
Section 3.1
EOM was received.
o

NSP
NSP preserves data order.
process,
single transmit buffer into the network form
guarantees
also
NSP
were 1in the buffers.
the data flow
3.1 details
Section
lost.
-

Messages

In order to provide logical 1link service,
(thereby supporting the Session
control

flow ' control and error
NSP
interface),
Control

They do so by sending
modules in different nodes must communicate.
consists of these
protocol
NSP
The
messages.
NSP
‘and receiving
messages and the rules governing their exchange.

There are three types of NSP‘messages:
.o

Data messages

0 Acknowledgmént messages
»o Control~messages'
Table 1 summarizes

the functions

performed by each

" Section 8 describes the message formats in detail.

NSP

message.

Functional

Page

Description

Table
NSP

Messages

+___...___. ______________ d e

| Message
S

Gvm

SRS

WML
VNS

SEES

TR
Gl

SEm
S

GRS

VINDS
AIDE

SEIUN

GENED AU
RN

MmOy

GRADN

UMM

SRS SAEME WAL

SIS

AN
WA

GMA

eGwA

Data

emed

|
T

GEDE

GOMD

Sugel

WED

GEN

GEME TEMN)

SEI

AN
G

MG
WGl

e ———— -.- —————————————————————— k.

Description
D

YNNG

MAUS

NGNS

EING

G
G

GmAn
WM

SEERS

RGN

GEER EEES

GEE
W

S
M

AGOE

GAEED CHAEN

VDS GEVE
MG

AR
VEIN

FEUG

WSS GMGE SENND
SEE

NGNS

WMAR

NN
M

MR GG

wm—

awm—

Carries a portion of a
Session
Control
message.
(This
has
“been passed to Session
Control
from
higher
DNA
layers
and
Session Control has
added
1its
own control information.)

Segment

Carries urgent data,
originating from higher DNA layers.

(also called

Other-Data)

Carries
data
flow
control
information
(also
called Link

Service message).

| Interrupt Request| Carries 1interrupt flow: control
(also
<called Link
| information
| Service message).
+

Acknowledgment

Data

Acknowledgment

|
|
|
|
|

Acknowledges receipt of
either
a Connect
Confirm
message or
one-

messages,

and

Data

Segment

optionally

Other Data message.

+ _________________________________ <+

OtHer Data

Acknowledgment

|
|
|

Acknowledges
more

receipt

Interrupt,

Interrupt

Data

Request

one

Request

or
or

messages.

| Connect
| Acknowledgment
|
|

|
|
|
|

Acknowledges
recelpt
of
a
Connect
Initiate
message
or
Retransmitted
Connect Initiate
message.

(to be continued)

———

Functional

Description

Page

Table
NSP

1 (Cont.)
Messages
_________________________________ +

Description

}

Carries a logical link
connect
request
from a Session Control
module.

|
|
|

_________________________________ +

Carries a logical link
acceptance
from
a
Control module.

connect |
Session |
a

————————————————————————————————— +

Disconnect
Initiate

Carries a logical link
connect
rejection or disconnect request
from a Session Control module.

|
|
|

_________________________________ +

Disconnect
Complete

Acknowledges the receipt

Disconnect
Initiate
message
(also called Disconnect Confirm

message) .
————

Sent when a message
is received
for
a
non-existing link (also
called
Disconnect
Confirm

message) .

|
|
|

|
+

|
|
|

————————————————————————————————— +

Does
nothing
(included
for
compatibility with NSP V3.1).

|
|

————————————————————————————————— +

‘Functional Description

2.6

Page

Major NSP Functions

This section summarizes the operation of the major'NSP functions which
include:

Establishing and destroying

Error control (Section 2.6.2)

Flow control (Section 2.6.3)

'SegmentatiOn and reassembly of user data

links

2.6.4)

logical

(Section

2.6.1)

messages

(Section

2.6.1
Establishing And Destroying Logical Links - A source NSP and
a
destination
NSP
exchange messages to establish and destroy (in other
words, to connect and disconnect) logical links.
Fiqures 3 through
7
summarize
the
message exchanges.
The calls in capital letters under
Session Control headings are names of interface functions as described
exchanges below will take place correctly
algorithms in Section 4 are followed.
N4

in Section 3.1.
The message
in an implementation, if the

|
| | Session
I

Control

-—————- |
|

NSP

{

| - I
|
|Session |
{

e el

o
|

|
|
|
:

|
|
|
|

CONNECT-XMT -->Connect

|
|
|
:

Initiate
.

= =

- NSP

]

—-—=———————-——- >

|
|
{

Connect
Acknowledgment

<————————
- Connect

Figure 3

|Control

LDl
TT

|
|

|
{

Confirm<-------- ACCEPT
|

Connection with Acceptance

]

Functional Description

Source

Page 19

Destination

|- |
| = —_—————
| Session
|
|
|
|Session
| Control
| NSP
|
|
NSP
|Control
| = -1
[ ==e
|
|
|
|
|
| CONNECT-XMT -->Connect
= -——---—- ———————— >
|

In:tiate

|
|

SourCe

a———
——
——
——— a—
s
/)

CONNECT-XMT

-->Connect

Kmmmmm

|
|

Acknowledgment

|
|

Disconnect

Initiate<------- REJECT

|
|
-—--—--—--————- >

b
|

Initiate

I
|
|

| ___________ —

e e —_—————

—————————e————— >

\‘V/’

——

|——————
| Session
|
| Control
| NSP
-

|
|

“

| Disconnect
|
Complete
W

<mmmmmm Connect

|
|

{

Figure 5

Connection Attempt with No Resources

Functional Description

Source

Page 20

Destination

| m
ittt
bt
| Session
|
a
|
.
|Session |
| Control
| NSP
]
l
NSP
|Control |
| === e
—
|
| mee- |
|
|
|
|
|
I
| CONNECT-XMT -->Connect —
——-=---- .
|
|
|
|

|
|
1

In1t1ate

|
|
|

(Connect

|
|
<---—-—-'
|

Figure 6

Initiate

returned to sender
by Routing)
g

|
l
|

|
|
|

Connection Attempt with No Communication

Source

Destination

|
{ |

I
:

'NSP

|-l
e
|
|
|

Session
Control

|
|

NSP

|Session
|Control

ey
[
[
U

| CONNECT
-XMT -->Disconnect -—---------==--=>

Initiate

I
|

|
|
A

ommn

ST MED GEN

S ERED GEUN

WD TN SN

EMD

SN SN

|
LR

S SR

|
|

|
SN

2.6.2

ST wsew e

Figure

ensure

AN AN ST

S G

GG WERS G

messages are

|
|
AUSE) SO

GENN WD

|
|

NG U TN

G SR RS

A em—

Disconnection

Error Control - NSP uses a basic acknowledgment
that

Complete

Disconnect

|
I

delivered.

mechanism

NSP does this for each of the

four data messages listed in Table 1, Sectlon 2.5.

On a logical link,

the four data”messages can be_thought of as

moving

in
two
subchannels.
One
contains Data Segment messages,
the other
contains Interrupt,
Data
Request,
and
Interrupt Request
messages

'(collectlvely known as Other-Data).

Messages

if each subchannel

transmitting
NSP.
quickly.
OtherW1se,

are 'nUfiBered seQUentially

by'

the

The
receiving NSP
returns
an
acknowledgment
the transmitting NSP retransmits the message.
It

Functional Description

not

necessary

acknowledge

each

message

Acknowledgment
of a given numbered message implies

all messages with a lower number

Page 21

individually.

acknowledgment

Section

Cknowledgment operation.
Flgure 8 deplCtS the ofsegment
the acknowledgment messages.
specifies the format

Figure 8

a—

to a message,

—

transmit number = n

Data-receiving

—

Data Segment Message|-->

—

[

an ca

transmit number = m
"Other Data" Message|-->

——

NSP

—

|
|
|--|

c—

——

—

|
|

/et ve——— d——

number

o———

Sm—

ua———

|
|
|
|
|
Data-transmitting
|
NSP

Segment'Acknowledgment Operation

The data transmitting NSP a551gns a transmit
transmits the message, and starts a t1mer.

of'

(modulo the maximum message number).

——— c— o — —

’is

—

If the timer times out, the message
is retransmitted.

f o
@

/. —

Data :Subchannels

If the timer does not time out, and the flow control mechanism
' allows another message to be sent, the data-transmitting NSP
assigns the transmit number plus one to the next data message
transmitted

that

e
|
|
|
| Data-transmitting

]

|
e ———————— .
|
transmit number = n+l|
|
|--|] Data Segment Message |-->|
|
~----------m
'
|

]

NSP

subchannel.

}

bbbl bttty .

| transmit number = m+l|

:——j

{

I
|
]
Data-receiving |

)

NSP

!
UGS

CEE

CHNE

VES

SN}

VNN

GRS

ANSE

"Other Data" Messagel-r>=
1

.=
I

Data Subchannels
>

I When the message with the f1rst transmit number is received by

the data-receiving NSP, it returns that number as an acknowledg-

ment

number W1th1n the

f1rstacknowledgment

Page 22

If the next

1is

equal

to the

NSP

—

)

Acknowledgment|

.-—-| Data

Message

———

|
1|

|
|

w—

receive ack.
number = n +

——|

|
|

w—

.
.

|
|

Data-

receiving
NSP

Data

The

data-receiving
NSP might

not

Sacrn C—
mee
S

S
—

amssm

—

——

—

transmitting=

—

transmit number received

——

i
—
——
—
——

Data-

—

data message

current acknowledgment number plus one, the data-receiving NSP
accepts the data message, 1ncrement1ng the acknowledgment number,
It then sends the new receive acknowledgment number back to the
data- transmlttlng NSP within an acknowledgment message.

———— C——— ———

) —

Functional Description

Subchannels

send

acknowledgment

for

number

each

implies

However, 1f the data- rece1V1ng NSP receives a data message transmit number less than or equal to the current receive acknowledgfor that subchannel, the data segment is discarded.
The data-receiving NSP sends an acknowledgment back to the datatransmitting NSP.
The acknowledgment contalns the receive
acknowledgment number.
|
.

——
-

P om—
I3

ment number

’

F e—

data message received.
The receive acknowledgment
that all previous numbers were received.
|

If the data-receiving
NSP receives a data message transmit number
greater than the current receive acknowledgment number plus one
for that subchannel, the data segment may be held until the
|
preceding segments are received or it may be discarded.

Figure
Segment

Acknowledgment

Operation

Functidnal Description
2.6.3
when

Page 23

Flow Control - Flow control is the
mechanism
that
determines
to
send
an
NSP
Data
Segment
or Interrupt message.
This

mechanism, along with the error
control
mechanism,
coordinates the
flow
of
data
on a logical link from transmit buffers in one node to
receive buffers in another node.

Flow control is performed separately for normal
Flow control operates
a logical 1link.

2.6.3.1

Normal

algorithms
1.

for

symmetrically

Data

Flow

for

data

Control - Flow

interrupt

data.

each dlrectlon

requires

two

An
algorithm
executed
by
a data-transmitting
determines 1f a Data Segment message may be sent.

addition,

data-receiving

NSP

messages

"on/off" control

may

"send/do not

send"

data-transmitting
message, the value

data base

mechanism

may

NSP

used

that

indicate
to a data-transmitting
NSP that Data

may

not

On/off control. On/off control is
control.
It operates as follows:

1in

An
implementation-dependent
algorithm
executed
by
a
data-receiving
NSP
that
determines
both
when
to send a
request message and the count value to be put into a request

Segment

and

—control

normal data:

message.

flow
g

indicator.

sent.

independent of
the
request
count
Each Data Request message contains

When the error control mechanism

NSP has
received
of the "send/do not

associated with the

logical

in a

and
accepted
a
Data
Request
send"” indicator is saved in the

link.

When the value

"do not

~send," the data-transmitting NSP may not transmit normal
data.
When
the
wvalue
1is
"send,"
the
data-transmitting
NSP exercises the flow
control mechanisms described next.
,
|

Request count flow control.
During logical link formation, the NSP at
each end
of
the link determines the kind of flow control 1t expects
when actlng as a data recelver., The term "data-receiving
NSP"
means
an NSP acting as a data receiver. There is a choice of:
o

Segment

flow control
flow control

Session Control message flow control

The choice’ of
flow
control
1is
1indicated
wvia
fields
1in
Connect
Initiate, Retransmitted Connect Initiate and Connect Confirm messages.

Functional Description

Page

Each data-transmitting NSP must accept the type of
flow
control
the
data-receiving NSP expects.
Note, Message flow control is obsolescent
and will be eliminated at a future time.

A data-transmitting NSP maintains a "transmit request count"
variable
for
normal: data in the data base associated with each logical link.
When the error control mechanism receives and accepts a
Data
Request
message,

flow

control

adds

the

count

value

from the message

the

appropriate transmit request count.
The count values contained in the
request
messages
may be zero, positive, or, in some cases, negative.
messages

are

|1]

NSP/Node A send a Connect Initiate message to NSP/Node B:
|

!2
-'

Connect

Initiate

|-—-—--—--=--————- >

NSP/Node B, having received the Connect Initiate message, returns
a Connect Confirm message.
A field in the message indicates that
NSP/Node

expects

segment

flow

control

<————mmmm
|

Connect
Confirm
-

want

segment

|3]

NSP/Node A's data base has the

count variable

|
!
14|
-'

for

FLOWrem dat=0
o~ T T T T T T T/ o
|

2
I

——— v

— - —— —— — — A _____ !

flow control"--------- '

initial value of

normal data segment

0 for

its

request

flow control:

—_"1

NSP/Node B sends Data Request message contalnlng a flow control
value that indicates the number of Data Segment messages NSP/Node
B can receive.
(NSP/Node B executes an implementation- dependent
algorithm to determine this value):

<m——mm—mm
o

can

Data
Request

:
:

I
|

A________l

receive n messages"---—--—-—--- '

|5] NSP/Node A sets FLOWrem-dat to n:
o

4\\

No
flow
control.
If
the
data-receiving
NSP
selected
"no
flow
control,"”
the
data-trarsmitting
NSP
may
transmit data at any time
(subject to the "on/off" constraint).
|

This
additive
scheme works
because
the
request
error-controlled;
1t would not work otherwise.

O
|
I

p—

Functional Description

Page 25

NSP/Node A executes algorithm to determine if Data Segment
Number 1 can be sent

(highest acknowledged Data Segment message

plus the current request count must be greater than or equal to

the number of the next Data Segement message sent):
*

(Q+n>=1?.

*--NO--can't send

|
YES

SEND

The answer to the above is YES, so NSP/Node A sends Data Segment
|

number

Data Acknowledgment

of segment number 1

Figure 9 Example of Segment Flow Control for Normal Data on
a Logical Link (shown in one direction only)

Segment flow control. Figure 9 shows an example of the operation of
segment flow control. Segment flow control operates in the following
If the data-receiving NSP selected the segment flow control
‘manner:
mechanism

when the logical link was formed, the highest numbered Data

Segment message that may be transmitted is the one whose number is
equal to the sum of the highest numbered Data Segment message that has
by the
mechanism)
control
been acknowledged (via the error
The
count.
request
the
of
value
current
the
plus
NSP
iving
data-rece
for
one
by
variable
count
request
its
s
decrement
NSP
smitting
data-tran
each Data Segment message acknowledged by the data-receiving NSP.
The count values that can be contained in Data Request messages may be

Functional Description

Page 26

negative.
This
means
that
the permission to transmit a particular
Data Segment message (even if it has been previously transmitted)
may
be
withdrawn
by
the receiver.
This, in turn, causes an interaction
between the flow control and error control mechanisms.
Specifically,
it
1s
not
necessary
for the error control mechanism to maintain an

active retransmission timer for a Data Segment message that

transmitted
other words,

at
to

least

once

retransmit)

but
has

for

which permission

been withdrawn.

has

to transmit

been
(in

Session Control message
fiow
control.
If
the
data-receiving
NSP
selected
Session
Control message flow control, the data-transmitting
- NSP cannot send a segment if the
number
of
end-of-message
segments
between

the

(exclusive)

highest

1is

acknowledged

greater

than

segment

and

equal

data-transmitting NSP decrements its request
each
Data
Segment
message
that
1is
an
acknowledged by the data-receiving NSP.

the

segment

the

question

count.

The

count variable by one for
end-of-message
segment

The mechanism for Session
Control
message
flow
control
does
not
interact
closely
with
the
error
control
mechanism (unlike
the
mechanism for segment flow control).
Once a
Data
Segment
has
been
given
permission
to
be
transmitted,
the
permission will never be
withdrawn,
|
-

2.6.3.2

Interrupt Data Flow Control - All

NSPs

use

interrupt

data

negative.

The

flow
control for moving interrupt data.
This mechanism is similar in
operation to the
Session
Control
message
flow
control
mechanism.
Interrupt message
request
counts
are
carried in Interrupt Request
messages.

The

counts

are

interrupt-transmitting
transmit request count.
an
implicit
request
transmitting NSP cannot
Interrupt

and

the

messages

Interrupt

additive

and

may

not

NSP
can,
therefore,
maintain
an
interrupt
When a logical link is established, there 1is
of
one
interrupt
message.
The
1interrupt
send an Interrupt message if
the
number
of

between

the

highest

acknowledged

message

Other

Data

message

in question is greater than or equal to
the
The 1interrupt-transmitting
NSP decrements its request count
by
one
for
each
Interrupt
message
acknowledged by
the

count.
variable
interrupt-receiving NSP.

2.6.4

Segmentation

And

Reassembly

User

Messages'— Because

network
constraints
such as availlable buffer sizes and transmission
error characteristics, user messages in Session Control buffers cannot
always
be
.sent in one piece.
A data-transmitting NSP breaks
up data
contained in
a
single
Session
Control
buffer
into
segments.
A
data-receiving
NSP reassembles
the segments.
The data-transmitting

Functional Description

Page 27

NSP transmits the segments by means of

~data-receiving
NSP
puts
into the correct sequence.

Data

Segment

messages.

The

the segments from
the Data Segment messages
These messages contain user data
as
well

as
NSP header information.
The segment acknowledgment scheme (Figure
8, Section 2.6.2) ensures that all data segments' are
received.
The

data- transmlttlng

NSP must know the maximum length of

ThlS

lesser

length

the

of:

a Data Segment

The size of a transmit buffer in the source node.
This
size
cannot be larger than the node's Routing Layer will permit.

The maximum length that the data-receiving NSP
can
receive.
The SEGSIZE field in the Connect Initiate and Connect Confirm

messages,
exchanged when
contains this infcrmation.

the

1logical
|

1link

was

formed,

The data-receiving
NSP orders the data
segments using the
sequence
number
contained
1in
the
Data Segment
message
and end-of-message
information.
When Data Segments have been recelved out
of
sequence,
they
are
either
discarded
or
stored temporarily in a cache buffer

(Section 2.7.1).

This document does not specify the detailed processes of

segmentation

and
reassembly.
However,
Sections
6.5 and 6.8 provide a model
implementation and Appendlxes B and C provide examples.

2.7

Functional

Components

In its relation to DNA, NSP can be considered

for

"black

box,

which

modules.

Brief

interfaces
to Session
Control and Routing by defined 1nterfaces and
with
other
NSP
modules
by
the
Network
Services Protocol.
The
functional components in. this section and in Sections 5 and 6 describe
the operation of this "black box" by means of a sample implementation.
Any
other
implementation
with
equivalent
operation
1s
also a
legitimate NSP

implementation.

NSP

consists

data

bases,

buffer

pools,

and

descriptions
of
each
follow in this section. Section
5 details the
data base and buffer pool
specifications.
Section
u
specifies
1in
detail
the
operation
of the NSP modules with a model 1mplementat10n
written in a high-level,
colloquial computer
1language.
Figure
10
shows

the

interrelationship of

the NSP components.

Functional Description
2.7.1
NSP

-~~~

Page 28

Data Bases And Buffer Pools - The follow1ng is a model

of the

data

bases'

NSP 1nternal,data base. The NSP internal
data base
contains
NSP's
internal
variables and parameters. Variables are values defined by
'NSP.
Variables change automatically
during
the operatlon
of
NSP.
Parameters
are values
defined
by the Network Management interface.
Parameters can be read and sometimes set by the user.
Many parameters

are

static

the sense that they remain set untll the user changes

them.

Session Control port data base.
The Session Control port
data
contains
the port variables that NSP uses to manage a logical
When a logical link is created, NSP allocates a Session
Control

1t.

When the

port

data base

link

is destroyed

as a free

Reserved port data_base.

port

variables

base
link.
port

NSP releases the port back to the'

port

reserved

The reserved port
for

manage the sending of messages
Control port data base.

data

NSP's internal use.
that

not

map

base contains
NSP uses

onto

the

these

the

Session
o

| SESSION
| CONTROL

INTERFACE |
ROUTINES |

|~
fmmmm——————mm—————— '

[

mmmees '
v
| CACHE |
e.
I REASSEMBLY | <—->| AND
I

I MODULE

PORT

| COMMIT|

xVa

Lo .

]

ittt

TRANSMIT

———————

|
|
]
e

v
e —mm—— .
SEGMENTATION |

| MODULE

| RECEIVE

—————————— . g
}

————,

| TRANSMIT |

,-====-——----,

—————————-']

| LARGE

| RECEIVE

| POOLS |

DATA |<-=—————- > | PROCESSES I
| <==———=- >|
| PROCESSES
—-——---—---- '
BASES |<-----,
|
Cem e '
I
B ittt '
|
|
I
I
I
|
I
|
I

Page 29

|
|

Functional Description

Somm .
kbt '

|RECEIVE|

| BUFFER |

Figure 10

POOLS

Interrelationship of NSP Components

The node data base contains a collection of node
Node data base.
node descriptor is required for each remote node to
A
descriptors.

which a logical link 1is
variables and counters

A node descriptor contains
established.
pertaining to communicatlons with that node

(for example, the estimated round trip communlcatlons

delay,

traffic

The large and

small

transmit

usage and error counters)

Large and small transmit buffer pools.

buffer pools contain large and small transmit buffers. Large transmit
buffers transmit Connect Initiate (or Retransmitted Connect Initiate)

Functional

messages

Description

or Data

Segment messages.

all other NSP messages.
transmit buffer pool for

Receive
recelve

Page

Small transmit buffers transmit

An implementation may
all NSP messages.»

choose

use

single
|

buffer pool.
The receive buffer pool contains a collection
buffers required to receive an NSP message from Routing.

" Commit buffer pool.
The commit buffer pool is an optional pool
which
contains
commit
buffers
wused
for
data that the receiving node may
commit to storage even in the absence of receive buffers supplied
by
Session Control.
Such data may be acknowledged to its transmitter.
Cache buffer pool. The
contains
a collection
Data

Segment

are

out

buffer
or a
Event

order

that cannot

because

Session Control

buffer

queued

messages

cache buffer pool
of cache buffers.

pool.

to NSP's

The

event

queue

buffer

for

optional
pool
which
buffers hold received

acknowledged

there

receive

is an
Cache

pool

reading

for

because

either

they

commit

them.

contains

buff er o~
>

L hat
by Network Managem ent

2.7.2
Modules - NSP modules perform specialized
two kinds of modules:

either

storage

functions.

A process is a module that is independent of

may

There

other

are

modules,

but
uses the services of some other modules. It is designed
as 1f it were executlng On a processor dedicated to it.
2.

A
-

routine

processes,

general,

a module

but

processes

does

that

not

provides

have

communicate

with

functions

context
routines

its

for

one

or more

own.

by means

calls

and

with
other
processes
by
means of shared variables, usually a port.
The mechanisms that synchronize two processes to prevent common
entry
to a cr1t1cal region are not explicitly defined.

The NSP process and routine modules are described

below.

Note

that

these are functional descriptions of components.
Implementations
not be structured exactly as outlined in these descriptions.

Interface routines.

The interface routines handle all Session Control

calls (Section 3.1).

Receive ‘dispatcher
receive

buffer

routine,

pool.

Receive processes.

The

recelve

dispatcher

manages

It polls Routing for received messages,

them, maps them onto
ports,
approprlate NSP process.

Communications

need

and

returns

message

contents

the

parses"

the

These receive and'handle NSP messages from the End

Layer

remote

nodes

and help manage

logical link

\\J }

Functional Description

states.

Each Session Control port has a set of

"Page 31

these processes.

Reassembly
routine.
The
reassembly
routine
determines the
flow
control
policy,
maintains
the
cache
and
commit buffer pools, and
reassembles
received
Data
Segment
messages
1into
Session Control
receive

buffers.

Transmit processes.

‘messages

Control port

These transmit (and retransmit,

End Communications Layers at

has

a set of

if necessary) NSP

remote nodes.

Each Session

these processes.

Transmit format routine.
The transmit format routine maintains
large
and
small
transmit
buffer
pools and formats outgoing messages.
It
queues messages
to
Routing.
It
polls Routing
to
get "transmit
complete”

notifications.

Segmentation routine.
buffers

messages.

into

form

This segments data in Session Control
suitable

for

transmission
‘

1in
,

Data

transmit
Segment

Transmit allocation routine.
The transmit allocation routine receives
requests
for
perm1551on to transmit from the transmit processes.
It
allocates permission to transmit in a way that
gquarantees
that
when
more
than
one logical link is established to the same destination at
the same time each provides useful communication services,

3.0

NSP INTERFACES

This sectioh describes the three external NSP interfaces:

The

Session Control

Network Management interface

Routing interface

interface

following

interface

functions are described as calls to subroutines

1in the

format:

FUNCTION (1nput;

output)

Descriptions of input and output then follow unlesspreviously given.

In general, there are two types of subroutlne5°

function
for

that

transmitting

completed

rece1v1ng data..

For buf fer-queueing calls,

immediately,

additional

‘those

performing

and those queuelng a buffer

«calls

are

defined

polling
to
obtain
"buffer
returned"
notifications.
A
argument denotes a system-dependent buffer
descriptor
that

allow

"buffer"”
contains

location
and
1length
information.
A "port id" is a system-dependent
number identifying a port.
Although not described
1in
the
following

NSP

Interfaces

functions,

invalid port

identifier

causes

Page

error.

Note that an implementation 1s not required to code the interfaces
calls to subroutines.
The calls specify functions only.

It may be useful
to refer to the port state

4.1

when

studying
the following

interface

descriptions

1in

functions.

Section

3.1

Session Control

This
link
more
same

i1nterface allows NSP to provide Session Control with the
logical
service.
This
service allows Session Control to create one or
logical links to one or more other Session Control modules in the
network.

In the

Interface

interface descriptions,

the terms

"source"

and

distinguish
the
requester
of
a
function
from the
request.
The source and destination can be within
a

"destination"
receiver of the
single
Session

Control module or in two separate Session Control modules.
single node, a Session Control module can communicate with

Thus, at a
itself
via
~a
logical
1link;
Dbetween two nodes, two Session Control modules can
communicate with each other via a logical 1link.

The calls, described by function, are as follows:

STATUS (;

NSP status)

returns:

NSP
NSP

is halted.
1s

running;

(NSPbuf -- Table 3,

minimum

receive

Section 5.1)

buffer

size

returned

This function reads the status of NSP
and
obtains
a
minimum
receive buffer size 1f NSP 1s running.
This is the one Session
Control interface function that does not 1nvolve the use
of
a
logical link.
.

OPEN

(source,

buffer;

source:
|

return)

a lé6-bit buffer to contain the logical link,requéster‘

node

address

request

returns:

when

this

node

receives

connect

port allocated and port identifier returned
port not allocated -- insufficient resources

port not allocated -- NSP halted

‘

" This function allocates a pbrt in NSP for receiving

logical

link
connect
request.
The source variable receives the
address of
the
requesting
node;
the
buffer
receives

node
the

NSP Interfaces

Page 33

incoming
connect
data.
When
the
port
incoming connect request 1s received,
NSP
node
address
1in
the source variable and
the buffer.
|

(port

1id)

This

function deallocates

a port.

When

state
1indicates an
places the
source
the incoming data in
|
|

a port

closed,

NSP

immediately returns all transmit and receive buffers to Session
Control (see DATA-XMT and DATA-RCV
calls).
Once
a
port
1is
closed,
1its
associated
port
identifier
1is
wundefined.
Any
subsequent
an

error

call

1ssued with such

a port

identifier

return.

results

1in

Session Control may close a port at any time regardless of
the
port's state.
However, doing so may create ambiguities for the
Session Control module at the other end of the logical link.

CONFIDENCE

(port

returns:

id;

confidence)

network probably connected
network probably disconnected
port

not

in RUNNING,

DISCONNECT-REJECT,

CONNECT-CONFIRM,
DISCONNECT-INITIATE

state

This function obtains NSP's assessment
of
connectivity. NSP
periodically
tests
a
logical
1link
once
it
1is
formed
to
ascertain
if
the
physical
path
supporting
the
link
is
connected.
The result of this testing is-the probable state of
connectivity.
It is not a guaranteed state.

Session Control may
issue
disconnect a link on behalf

STATE (port

id;

returns:

this
call
to
determine
when
of a program at the user level.

state)
the state of the associated logical link

This function returns the state of a port that is not CLOSED.
Because NSP's operation 1s not
necessarily
synchronized
with
that of Session Control, it is possible that this call will not
detect every state transition.
This 1s especially the case for
state
transitions
that
occur very quickly.
However, this is
not a problem because the 1nterven1ng undetected states can
be
log1cally deduced.

NSP

Interfaces

‘Page 34

CONNECT-XMT (destination [,circuit [,nexthopl], buffer;
destination:

return)

destination node address

circuit:

internal NSP mechanism

loop

testing.

selector

Circuit

1is

used

‘normal use)
or
a
system-dependent
representing
the
circuit
NSP is

messages estabiishing this logical
Management

loop tests).

‘nexthop:

a node number
circuit)

(required

‘buffer::

contains cohnéct data

refiurns:

port allocated;

enable

circuit
to
use

number
for its

either unspecified
link

(for

«circuit

(for

Network

broadcast

port id returned

port ncf allccatéd -—- insufficient resources
port not allocated -- NSP halted
requests

logical

1link

set

CONNECT-STATUS

returns:

"unspecified."

(port

id,

buffer;

return)

connect request accepted by destination

port

connect request rejected by destination --

port

RUNNING state;

REJECTED state;
port

accept data

reject data

returned

in buffer

returned

in buffer

neither RUNNING nor REJECTED state

This function obtains
result
of a previous

accept
or
reject
data
returned
as
a
connect request.
If the return 1s one of
the first two, NSP returns any available accept
or reject data.
Once
this
1is done, an NSP implementation may discard 1its copy
of the accept or reject
data
so
that
a subsequent
connect
status function would not return data.
|
|

In cases where state transitions occur
Control

may

not

be able

very

to perceive some

Consequently,
this call may not be accepted

rapidly,

Session

intervening states.

(see Section 4.1).

| ///

and

connection.
After a logical link has been successfully formed,
Session Control can put a load on a
particular
physical
1link
for
1loop
test
purposes
provided
that
the circuit argqument
specified the physical
1link.
This
enables
testing
of
the
physical
1link
and
all
of
the
DECnet
modules from Session
Control or higher layers by sending and receiving data
on
the
resulting
logical
1link.
For normal use, the circuit argument

This function allocates a port

NSP

Interfaces

Page

Accept data will be lost if the
rapid state
transitions
with a transition to the DISCONNECT-NOTIFICATION state and
call was never executed 1in the RUNNING state.
No data is
otherW1se
|

end
this
lost

If the connect request is accepted, up to 16
bytes
of
accept
data may be returned in the buffer.
If the connect request was
‘rejected, up to 18 bytes of reject data may be returned in
the

buffer

(port

(see

id,

the ACCEPT

buffer;

returns:

link

and REJECT calls).

return)

accepted

port not

in CONNECT-RECEIVED state

This function accepts a connect request from a
remote
Control module.
The call supplles a buffer containing
bytes of accept data.

REJECT (port id, value, buffer:

)

returns:

Session
to 16

return)

1link rejected
port

not

CONNECT-RECEIVED

state

This function rejects a connect request from a Session

module.

The

containing up

call

supplies

bytes of

2-byte

reject

data.

wvalue

and

Control
a

buffer

i) DISCONNECT-XMT (port id, value, buffer' return)
returns:

This

call

accepted

call

rejected

function requests

1in

buffer

the

RUNNING

contalnlng

the

state.

port

not

RUNNING

disconnection of
The

call

bytes

supplies

state

logical link
a

2-byte

disconnect

value

that
and

data.

The remote Session Control module receives any data transmitted
by the disconnecting Session Control module prior to this call.
Session Control disconnects a link when it has no more data
to
send
and
wants
to
ensure
that
the
1link
will be properly
disconnected, not aborted.
|
|
|

NSP Interfaces
ABORT-XMT

(port

returns:

.
id,

value,

call

buffer;

Page 36

return)

accepted

call rejected -- port

not

in RUNNING state

This function requests the immediate disconnection
of a logical
link
that 1is in the RUNNING state.
The remote Session Control
module may not receive all previously transmltted
data
before
rece1v1ng the abort notification.
The call

supplies a 2-byte value

bytes

abort

data.

and a buffer containing up
|

DISCONNECT-RCV (port id, value, buffer;
returns:

disconnect data
no disconnect

to
|

return)

available

data

availlable

port not in DISCONNECT-NOTIFICATION state
This function receives disconnect data returned
to
the
local
Session
Control
module as
a result
of a DISCONNECT-XMT or
ABORT-XMT call from the remote Session Control module.
Session
Control detects a logical 1link disconnection or an abort when a
STATE call returns a DISCONNECT-NOTIFICATION.
A
2-byte
value
and up to 16 bytes of data may be returned in the buffer.
-

DATA-XMT

(port

xmtflag:

id,

buffer,

return)

a flag.indicating whether the last byte in the buffer

is
the
value 1s

last byte
one of:

a Se551on Control message.
~

end-of-message

qot—ehdhof—message

Section
returns:

xmtflag;

2.4.4

describes data

Its

flow.

buffer queued

buffer not'queued -— insufficient resources
port

not

in RUNNING state

This
function
queues
a
transmit
buffer to
transmitting
normal
data on
a logical link.

queue the buffer either
if

th'e port is not

a
port
for
NSP refuses to

it lacks the resources to do

in the RUNNING state.

NSP Interfaces

Page 37

XMT-POLL (port id;
returns:

return)

no tranmsit complete'
transmit complete -- buffer descriptor returned

"This function returns a transmit buffer to Session Control.

DATA-RCV (port

id,

fcvflag:

buffer,

a flag indicating whether data truncation is allowed.

\v/

o
"returns:

return)

It may have either of the

rcvflag;

following values:

no truncation allowed
truncation allowed

Dbuffer queued

buffer not queued --

insufficient

buffer

not queued

buffer

resources

too

truncation was specified in rcvflag

small

and

no
-

| port not 1in RUNNING or DISCONNECT-INITIATE state

This function queues a receive buffer
to
a
port to
receive
normal data.
A "buffer too small” return indicates the buffer
size is smaller than the minimum receive buffer,
NSPbuf
(see
STATUS)
.

Session Control
may provide
a
buffer
to
a port
1in
the
DISCONNECT-INITIATE state
to avoid a Session Control deadlock

which

each

end

DISCONNECT-INITIATE

implementation-dependent

RCV-POLL

(port

returns:

id;

the

state.

logical

- However,

1issue.

link

1is

the

buffers

are

this

return)

no buffer returned (Either

queued

available.)

the

port
o

or
|

receive

there 1is

no receive data
|

buffer returned -- no data lost, end-of-message
buffer returned
-- data lost, end-of-message

buffer returned -- no data lost, not end-of-message
buffer returned -- data lost, not end-of-message

NSP Interfaces

buffer

Page 38

returned

empty

DISCONNECT-INITIATE,

port

not

RUNNING,

DISCONNECT-COMPLETE,

DISCONNECT-NOTIFICATIO
states.
N

This function obtains a "receive complete" notification
for
a
receive
buffer
previously
queued
via
a DATA-RCV call.
NSP
returns
receive
buffers
along
with
buffer
descrlptors
to
Session Control in the order in which data was placed in them.

A data-transmitting NSP
DATA-XMT

call

and

seaments

sends

each

data

given

segment

separately

network.

Dby

through

the
the

A segment
containing
data
given to
NSP
with
an
"end-of-message"”
flag
1is
so
marked.
A
data-receiving NSP
segments

and places

given
to
packets flowing

sequence of
data-receiving
Section 2.4.4.

NSP

the data

Session

Control

NSP by the DATA-RCV function.
The
from a data-transmitting NSP
to
a

constitutes

'the

network

form described
~

If a data-receiving
Session
Control
module
gives NSP
each
receive
buffer with the rcvflag set to "no truncation allowed"
on the DATA-RCV call, then NSP attempts to place the
data,
in
order,
from
one
or more segments of a single Session Control
message into each receive buffer.
A receive buffer
1is
always
returned ~with a "no data lost" indication and is returned with
an "end-ofmessage" indication if and only if the last
segment
of data placed in it was marked as an "end-of-message" segment.
Note that two DATA-XMT calls by the
data-transmitting
Session
Control
module,
one
with
data
that
1s
not
marked
"end—of—message"
and
the
second
with
no data but
marked
"end-ofmessage,
may result in data and status being given to
the data- receiving Session Control either in
two buffers,
as
given

NSP

the

data-transmitting

Session

containing

data

or in a
single
buffer
"end-of-message."
|

the

Control

and
|

module,

marked

If a data-receiving Session
Control
module
gives
NSP
each
receive
buffer
with
the rcvflag set to "truncation allowed,"
then NSP either fills the receive buffer or puts data
into
it
up
to
and
including the
data
in
a
segment
marked
as
"end-of-message” whichever comes first.
If a receive buffer is
filled
first,
then NSP continues to receive and discard data
segments

"end-of-message."
returned

case

where

and

1including

either

"end-of-message”

data was

discarded,

the

first

one

marked: :

receive

buffer

case,

the

RCV-POLL

the

receive

call.

buffer

with a "data lost" indication.
The only time
a
w1th
a
"truncation
allowed"
rcvilag
1S

"not-end-of-message" is when the logical link
by
the
data-transmitting
Session
Control
partially transmitted message.

is
the

returned

buffer
given
returned
as

is
disconnected
module
with
a

A data receiving Session control module may mix calls with
the
- "truncation allowed" rcvflag with calls with the "no truncation
allowed" rcvflag.

)/!

these

buffers

\_\

recelves
receive

NSP Interfaces

)

If Session Control closes

queued

via

the

INTERRUPT-XMT

(port

id, buffer;

immediately.

returns:

)

port that has

call,

NSP

receive
these

buffers
buffers

return)

accepted

data

not

accepted

port

not

in RUNNING state

destination Session Control module.

The data has no sequential

relationship
to normal data transferred on a logical link.
NSP
may
refuse a request to send interrupt data if it is unable
to
queue the data 1nternally
The buffer may be up
to
16
Dbytes
long.

INTERRUPT-RCV (port id, buffer;

i> |

returns

This function sends up to 16 bytes of high priority data to the

data

DATA-RCV

Page 39

return)

| v’returns: ‘data returned

no.data returned
port not

in RUNNING state

This function»obtains available interrupt data.
is

delivered

function.

1in

the

order

transmitted by the

Interrupt data has

sequential

normal data transferred on
a logical

3.2

link.

Interrupt data

INTERRUPT-XMT

relationship

Network Mahagement Interface

Network Management can perform the
Network Management

interface:

following

functions

wusing

NSP's

1. Initialize or halt NSP.

Read and set some of NSP's local parameters and variables.

Read NSP s remote node varlables and counters.
remote

)

node

counters.

Clear

NSP's

Read (one event at a time) and clear NSP's event queue.

The interface is modeled as a
subroutines.

Each

call

collection

represents

functions

specific

provided

function.

In each

NSP Interfaces

return, the variable 1n parentheses is its name
base descriptions in Tables 3 and 4. Section 5.

appearing

Page 40
the

data

Many of the calls pertain to either local or remote
NSPs.
Actually,
‘the "remote" NSP 1s the local NSP if the logical link is made within a

single

node.:

All the variables read, set,
or
<cleared
by
the
following
Network
Management
functions
are locally kept variables.
Thus, a set of NSP
variables for each remote node to which there
is
an
active
logical
link
1s
kept
at
the
local
node.
NSP does not guarantee that any
information will be available when there are no logical llnks to
the

specified remote

node.

Implementatlons of Network Management are not
parameter, variable, or counter listed here.
The

Network Management

interface

requ1red

functions

are

the

NSP.

return

every

follows:

INITIALIZE

This_function

initializes

local

HALT

This function halts NSP.

The call has the following effects:

l. NSP closes all ports.

2.
3.

NSP will refuse to open é'new port.
NSP

returns

all

Session

Control

its

counters

and

buffers

Session

Control.

NSP

freezes

LOCAL—READ—ADDRESS (:
return:

This

address

reads NSP's

LOCAL-READ-INACTIVITY (;
returh:

queue.

address)

NSP's node

function

event

(NSPself)

node

address.

inactivity)

NSP's inactivity timer (NSPinact
tim)

This function returns the interval after which,

1f there is

Page 41

NSP Interfaces

data going in either direction on a link, NSP checks the link.
NSP checks the link by sending a Data Request message (Table 1)
This message does not change flow control
to the remote NSP.
but does require an acknowledgment.

parameters,

LOCAL-READ-DELAY (;

return:

delay)

NSP's delay factor (NSPdelay)

This function returns the number by which to multiply one
the estimated round trip delay to a node to set
sixteenth of
The round trip delay 1is
the retransmission timer to that node.

used

an NSP algorithm that determines when to retransmit a
|

message (Section 7.3).

LOCAL-READ-WEIGHT

return:

(;

weight)

NSP's delay weight (NSPweight)

the current

applies

This function returns the weight NSP

round trip delay estimate to a remote node when updating the
estimated round trip delay to a node ( Section 7.3).

(;
LOCAL-READ-RETRANSMIT

return:

retransmit)

NSP's retransmit threshold (NSPretrans)

times the
This function returns the maximum number of
timer
sion
retransmis
expired
an
restart
will
NSP

deciding that the remote

node

unreachable

probably

source
Dbefore

(see

When this number is exceeded, NSP
CONFIDENCE ' in Section 3.1).
return to a Session Control
on”
disconnecti
"probable
a
gives

" CONFIDENCE call. Session Control may then disconnect the link
on behalf of the end user. The retransmit threshold is called
the

NODE

RETRANSMIT

FACTOR

Functional Specification.

LOCAL-READ-MAXIMUM-ACTIVE (;

return:

the

Network Management

DNA

maximum ports)

NSP's maximum ports number (NSPmax)

This function returns the

maximum

number

ports

NSP

has

concurrently had assigned to a logical link (in other words,
concurrently in a state other than OPEN or CLOSED).. This 1is
called NODE MAXIMUM LOGICAL LINKS ACTIVE in the DNA Network
Management Functional Specification.

NSP Interfaces

LOCAL-READ-TOTAL (;

return:
ThlS
the
in

NSP's total ports number (NSPtotal)~

function

returns the maximum active logical llnk count for
is the total number of ports that NSP can have

This

concurrently.

DNA Network

return:

This

Management

LOCAL-READ-VERSION

called

Functional

(;

version ‘number

NSP's

version number

NODE

MAXIMUM

LINKS

the

value

(qualifier,

qualifier:

one

returned

the

Specification.

(NSPver51on)

This functlon returns the local NSP's version number

version,

LOCAL-SET

- Page 42

total ports)

node.

use

4.0,

For this

value)
of

the

following,

defined

above:

LOCAL-SET-ADDRESS
LOCAL-SET-DELAY

LOCAL-SET-INACTIVITY
LOCAL-SET-MAXIMUM
LOCAL-SET-RETRANSMIT

LOCAL-SET-WEIGHT

value:
|

the new numerical value
variable.

for

the

selected parameter

This function sets NSP local parameters.

REMOTE-READ-DELAY (node: delay)
node:

return:

the

node

address

estimated

(NODEdelay)
This

round tr1p

delay

function returns the estimated round

remote

node.

the

trip

remote node

delay

the

Page 43

NSP Interfaces

active)

\) REMOTE-READ-ACTIVE (node;

the number of active logical links to the remote
|
(NODEactive)

return:

NSP

of ports in a state other than
This function returns the number
to the remote
OPEN that NSP has associated with logical links
1in the DNA
node. This variable is called NODE ACTIVE LINKS
Network Management Functional Specification.

bytes received)

REMOTE-READ-BYTES RECEIVED (node;

the number of user data bytes received (NODEbyt_rcv)

return:

of user data bytes
" This function'retUrns the total number
including normal,, interrupt,
received

connect,

the

from

node,

remote

reject and disconnect data.

accept,

REMOTE-READ-BYTES SENT (node;

bytes sent)

the number of user data bytes sent (NODEbyt xmt)

returns

This function returns the total number of‘user data bytes sent
to the

remote node.

REMOTE-READ-MESSAGES RECEIVED (node;
return:

messages received)

the total number of messages recelved f rom the remote

node

(NODEmsg_rcv)

This function returns the total number

messages

received

disposition.

from

remote

types

NSP

node regardless of thelr

This includes detected duplicates.

REMOTE-READ-MESSAGES SENT (node;

return:

the

of all

messageS'sent)

remote
the total number of NSP messages sent to | the o

node

(NODEmsg xmt )

Th1s function returns the total number of NSP messages sent

the remote node.

This includes retransmissions.

' NSP Interfaces

Page 44

REMOTE-READ-CONNECTS RECEIVED (node;

return:

connects received)

the total number of
received

from the

NSP

remote

Connect
node

Initiate

messages

(NODEcon rcv)

This :function returns the total number of NSP Connect ‘Initiate

messages

the

regardless

'local

their

REMOTE-READ-CONNECTS SENT
return:

has

received

(node;

from

the

remote

sent

returns
to

the

connects

the

remote

sent)

number

return:

NSP

sent

connects rejected)

the number
of received NSP Connect Initiate
for

which

there

was

to
|

Connect Initiate

node.

REMOTE-READ-CONNECTS REJECTED (node;

node

the number of NSP Connect Initiate messages
the remote node (NODEcon xmt)

This function
messages

node

disposition.

messages

no openvport'(NODEcon_rej)

This function
returns
the
number
of
NSP
Connect
Initiate
messages
rejected
by
the local NSP.
This variable is called
"received
connect
resource
errors"
in
the
DNA
Network
Management Specification,

REMOTE-READ-TIMEOUTS

(node;

returns:

number

the

"This
from

timeouts that

for

acknowledgments

node

(NODEtimeout)

function
the

timeouts)

returns the

destination

value:

the

occurred
kind)

from

the

waiting.
remote

number of

numerical

qualifier.

qualifier:

have
any

response timeouts

received

NSP.

REMOTE-READ-AN
(node,
D-CLEAR
value;

(of

qualifier)

wvalue

for

the

corresponding

one of the following, defined above:
o
o

REMOTE-READ-BYTES RECEIVED
REMOTE-READ-BYTES SENT

REMOTE-READ-MESSAGES

RECEIVED

REMOTE-READ-MESSAGES

SENT

- Page 45
©CO00O

NSP Interfaces

returns:

REMOTE-READ-CONNECTS

REMOTE-READ-CONNECTS REJECTED

REMOTE-READ-TIMEOUTS

the selected

This function
counter.

reads

RECEIVED

REMOTE-READ-CONNECTS
SENT

information

and

then

clears

node-dependent

NSP

return)
(;
READ-QUEUE
returns:

event

the

queue

first

following

empty

entry on

the

events:

event

queue.

One

the

invalid message

A
received
message
was
discarded
because
reserved
bits or values in the
message
were
used.
The beginning of
the message 1s the event data.

invalid flow control A

received

Link

Service

message
was discarded because
it contained a
request
count
that,
when used to compute an
accumulated
request = count,
would
produce a result out of
limits.
The
message
and
current request counts are the

event data.

data base reused
|

A
node
descriptor
5.4)
was
reused

events

The queue was

lost

(Section
for
a

different
remote
node.
The
contents
of the data base are
the event data.
|

full

when

attempted to place an entry
it.

One

or more

events

function reads the

first entry on

were

lost.

This

NSP

event

queue.

NSP

maintains
an internal event queue.
The length of the queue is
implementation-dependent, but is always
at
1least
one.
When
events
(described
above
in
the
returns)
occur, NSP places
entries in the queue.
If the queue is full when NSP
attempts

to place an entry in it, the last entry in the queue changes
to
"events

lost."”

The DNA Network Management Functional

Specification

describes

NSP Interfaces
return

Page 46

formats.

'CLEAR-QUEUE
This function clears NSP's internal event queue.

Interface

NSP requires a Routing service for
provides
NSP
with
the
ability

its
to

messages) to, and receive datagrams
same DECnet network.

operation.
A
Routing.
service
send
datagrams (containing NSP

from

any other NSP module
~

the
/

Routing

The interface described below appears
in the form of calls from an NSP

module

Routing module

ROUT ING-TRANSMIT
-

source:

the

same

node.

(source,

destination,

[,circuit[,nexthopl]],
buffer, tryhard;

a destination node address

returnflag:

a Boolean flag to

‘

circuit:

returnflag

return)

a source node address

destination:
'

indicate whether or not the

is
to
be returned by the
Routing
destination node is inaccessible.
The
one of the following values:

false

true -- return packet'

not

return packet

internal NSP mechanism

testing).

One of:

selector

(used

for

loop

unspecified

a
circuit
that
1is
the circuit
on
which
Routing
should
direct
this
datagram.
If
circuit specifies a broadcast circuit,
then
nexthop must also be specified.
|

nexthop:

buffer:

a buffer containing a packet

“tryhard:

a Boolean flag to indicate whether or not the
is

packet

service if the
flag may
have

node

number

sent

the

destination node

paCket

using

the

3.3

NSP Interfaces

)

'Page 47

RoutinglLayer's tryhard algorithm.

When this flag 1is

true,
NSP is instructing the Routing Layer to make a
maximal effort to deliver the
packet.
When
false,
"NSP
is
1instructing the Routing Layer to deliver the
packet using
a
less
costly and
potentially less
reliable mechanism.
The normal default is false.

returns:

buffer queued
buffer

not

queued

This function queues a transmit
rejects

call

(in

buffer

to Routing.

Routing

other words, does not queue a packet)

only if it has insufficient resources to queue the buffer.
If
‘the
destination
node
1is
currently unreachable, then Routing
accepts the
buffer, although
1t
may
return
the
buffer

this

> |

immediately

(see

ROUTING-CHECK-TRANSMIT-BUFFER

following). The "circuit" argument has
the
that in the CONNECT-XMT call (Section 3.1).

same
|

call,

meaning
|

ROUT ING-CHECK-TRANSMIT-BUFFER (buffer, return;)

returns:

all buffers remain queu:d by Routing

.i>‘

buffer returned to NSP
buffer:

buffer

previously

This function checks to see if
buffer

given

ROUTING-TRANSMIT call

can be

returned to NSP.

;) ROUTING-SUPPLY-RECEIVE-BUFFER (buffer;
returns:

to
.

previously
‘

Routing
.

queued

via

transmit

return)

buffer queued for receive by Rout ing
buffer not queued for receive by Routing

)

This function queues a receive buffer to Routing.

ROUTING-CHECK-RECEIVE-BUFFER (source, destination,
-

[,circuit[,nexthopl], buffer, tryhard;

source:

‘)

a source node

destination:

circuit:
|

return)

address

a destination node address
"

an internal NSP mechanism
testing).

One of:

selector

(used
|

for
|

loop

'NSP Interfaces

o
o

unspecified

0
|

nexthop:

node

returns:

all

Page 48

a
circuit
that
1is the
<circuit
on
which
Routing
should
direct
this
datagram.
If
circult specifies a broadcast
circuit,
then
nexthop must also be specified.
number

buffers

remain queued by Routing

buffer returned
with
addresses -- contains

buffer returned --

contains

packet

This

functign checks

buffer

4.0

NSP

can

to see 1if

returned

"retfirn

previously

node

sender"”

queued

receive

NSP.

the

states

and

state

transitions

required

for
|

Port‘States

Whenever

Session Control allocates

with

state.

data

and
destination
packet

STATES

ThlS section describes
normal NSP operation.

4,1

source
a normal

base.

exists.

The

This

state

CLOSED

state

a port,

NSP

associates

represented by a variable

really means

necessary

1in

that

the

port

architecture

the

port

in the port
no

longer

because the

remote port may be placed in the CLOSED-NOTIFICATION state.
In
some
implementations the CLOSED state may be indicated by the absence
of an
entry.
A port has only one state at a time.
Table 2
summarizes
the
normal port states.
|

NSP

Page

States

Table
Port

pommm
|

States

oo B S

(Symbol)

State

Explanation

The local Session
Control
has
1ssued
an
OPEN
call
which
created the port.
_________________________________ +

NSP

nas

received

Connect

Initiate
message.
(The remote
port
1S
or
was
in
the
CONNECT-INITIATE state.)
_________________________________ +

The local
issued a

port

Session
Control
REJECT call while

was

CONNECT-RECEIVED

has
the

the

state.

____;________4_________+ _________ +

NSP has received
Complete
message

Disconnect
while in the
DISCONNECT-REJECT state.
(The
remote

port

1is

has

been

1in

the REJECTED state.)
The

local

Session

Control

issued
an
ACCEPT
the
port
was
CONNECT-RECEIVED

call,
in

has

while
the

state.

The local Session
Control
has
issued
a
CONNECT-XMT
call,
which created this port.

(NR)

NO-RESOURCES

NSP has
message

received a No Resources
while
in
the

CONNECT-INITIATE

remote
NSP
did
available
port

state.)

state.

(The

not
have
an
1in
the
OPEN

NSP
has
received
its
own
Connect
Initiate
message
while in
the
CONNECT-INITIATE
state
because
Routing
was
unable
to deliver the message.

(CD) CONNECT-DELIVERED

NSP
has
received
a
Connect
Acknowledgment message while 1in
the

CONNECT-INITIATE

state.

(The destination port is or has
CONNECT-RECEIVED
the
in
been
state.)

NSP

States

Page 50

Table 2 (Cont )
‘

Port States’

+—___——_;——__;;—;—*;;;f—_—————T*;’—+—;*—__———;;g;f;;;f;—~f_-7-—f _____ +
I
I
|
|
I
I
I
I

»Explanatlon

REJECTED

(RJ)

NSP has

recelved a'=D1sconnect

‘Initiate message

while

CONNECT-INITIATE

remote port is or

has

the DISCONNECTREJECT
.

—

——

(RUN)

————

—

GaS

——

Gman

———

—

ou—

o—

——

RUNNING

the
or

CONNECT
DELIVERED ‘state.

=+ ———

|
|
|
|
|
|
|
|
|
|
|
|
|
|
|

State

(Symbol)

(The

been

1in

state.)

_________________________________ +

NSP
has elther received
a
Connect Confirm message while
in
the
CONNECT-INITIATE
or
CONNECT-DELIVERED
state
or
recelved a Data, Data
Request,

Interrupt

Request,

Acknowledgment

Data

Other

Data

Acknowledgment message while in
the CONNECT-CONFIRM state.
The
logical
1link
may be used for
sending and receiving
data.

(Either

the

remote port

entered

the RUNNING

is or

was
in
the
CONNECT-CONFIRM
state
or
the
remote port

state

from

the CONNECT DELIVERED state.)

_________________________________ +

|
|
|
|

The

local

Sess1on

Control

has

issued a DISCONNECT-XMT call
an

ABORT-XMT

RUNNING

call

whlle

the

either

state.

|
|
|
|
|
|
|
|
|
|
+

|
I
|
|
|
+

(DIC)

DISCONNECTCOMPLETE

NSP

has

Disconnect

recelved

Complete message or

a Disconnect Initiate
while
in
|
'DISCONNECT-INITIATE

(The remote port

state.

is or has been

~either

the

DISCONNECT-NOTIFICATION

message
the

the

state

DISCONNECT-INITIATE

state.)
—————---————-———-—_——————_———-———————-———

NSP has received
Initiate
message
RUNNING
state.

port

1is

has

Dlsconnect
while in the
(The
remote
been
1in the

DISCONNECT- INITIATE state.)

NSP States

Page 51
Table

Port
e

(Symbol)

State

(Cont.)
States
Fm

—————————

Explanatlon_

The local Sess1on Control
has
issued
a
CLOSE call (normally
‘while the local port was in the
DRC,

DN,

state).

DIC,

NC,

This
is not

really

state
of the port, but is
for
descriptive
purposes

indicate

that

the port

there.

(CN)

CLOSED- NOTIFICATION

NSP
has
message

is not
|

received

while

CONNECT-CONFIRM
remote

port.)

NSP

Link

RUN

the
|

state.

closed

No
in

DISCONNECT-INITIATE,

DISCONNECT-REJECT,

used
to

the

(The
remote

NSP

State S

Figure 11 ,
These

‘Page

following, summarizes the normal

tra nsitions

correspond with those

'
'

|++>|RUN

)

DR |+ ++++++>|

I
'

.————.

.~'"

| NC

|<———-"

I
C—é——.

|<++++++++]|
v

.
.—=

\
.————'

SS v

contains port state

——

VvV V
N
-——_C<-v
.—7

)

I
I
|

I
|J '

v
o——+——o
| RJ

——=-

v
- ===
| DN |

|
i |
R

transitions.

--------------- >|

state

|<++++++++++++++++++++++++++]| CD

\
.'_———.

v
e TTTT e
e~ T T T e
| DI
|++>|DIC |

port

in Table

(Table 2)

++++>

result from an action by NSP

_———>

result from a Session Control call
NOTES

A state from which am exit can be made by a ++++> arrow 1s
potentially unstable state.

"A state from which the only exits are -—---> arrows are stable
states.

A state

from which
an exit can be made only by more

++++>
arrow
is
non-deterministic.

Figure 11

state

from

which

the

than

exit

one

Port State Diagram

A transition to CLOSE from any state other

than

those

connected

NSP States

Page 53

the logical
arrows to CL on Figure 11 is equivalent to terminating
link while it was in a useful state.
Such a transition would occur,
This 1is the
when a user process terminates abnormally.
for example,
only kind of transition that can occur that is not shown in Figure 1l.

4.2

Logical Link States

when one Session Control module attempts to form a connection to a
second Session Control module NSP places the requesting port in the
NSP then attempts to assoclate the local
CONNECT-INITIATE (CI) state.
If
source port with a destination port that is in the OPEN (O) state.

The initial logical

is the logical link state.
of the two port states

logical 1link

implementations

can Dbe

that

transitions correctly.

1in

An NSP may fail to associate
following situations:

model

two

ports.

NSP

time.

Section 6 will make the

This

happen

can

the

the NO-COMMUNICATION state.

If there are no ports managed by the remote NSP

state.

NO-RESOURCES

state

one

the

If the network is disconnected so that the destination system
In this case, NSP places the requesting
is not accessible.

port

only

link state is represented as CI/O.

combination

the

" the association between the two ports is successful,

this

the

OPEN

case, NSP places the requesting port in the

state.

If the network is

not

(e.qg.

operating 'properly

is badly

succesive retransmissions fail, Sessions
and
congested)
the Confidence variable.
this by checking
detect
Control can

'Figure 12 shows the normal logical link state transitions.
The only state transitions that are not illustrated in Figure 12 are
those that represent the transition of one of the ports to the CLOSED
1is generally
Such a transition
state from a non-terminal state.
ICATION
CLOSED-NOTIF
the
to
port
other
the
of
transition
a
succeeded by
of
diagram
the
1into
ambiquity
introduce
transitions
state. These
of
kind
this
of
example
an
shows
12
Figure
transitions.
1link
logical
ambiguity in the exits from the CL/DI and DI/CL states. Figure 12
"does not show this complete set of transitions, because there are too
they
Moreover,
many to represent coherently in a single diagram.
a
of
operation
normal
during
occur
that
transitions
the
"obscure
logical. 1link.

Note:

1In certain unlikely cases a port in the open state may match up

when the
for connection (for example,
with a duplicate request
to be
appear
will
data
connect
The
rejected).
was
connection
original

NSP States

valid.
If
connection

the
the

receiving
1local
port

Page

session
control user accepts this false
will
never
enter
the RUNNING
state.

However,
1f communication exists with the remote node, the local port
will eventually enter the "CN" state.
Because of these cases, a
user
program
which
does
not
wish
to
process the data from a duplicate

connect should accept incoming connections
and process
data only if the connection enters the RUNNING state.

the

connect

this state if the port that is still

’

_——

———

————

S
.____

| R |---=>] RJ |

I—ié—u;*

-,1 DI

IDI

IDIC

CL |<--|DIC
DN |
|IDN

|DIC

CcL

|
|
|

’
|
|
|

|
I
|

'n~————;

Sk
T Tk T T

—

|++>|DRC [ CL|

) e

g____

lDI

DRCI

‘____l,

'————,*

CL |

——

|++++>|

_+__

omal

CD |-->| CcD

— —

LSSl

‘

~f_¥-

’

|
|

is closed by Session Control.

}
|
V

A
|
|

open

f mm— e——

Page 55

* An exit 1s made to the CL/CL state from

o ,; -

NSP States

+++++++++++++++++>.——-—,*

|----------—=—--——-——-->|DIC
|
|
|
|cL
v

|
|

12 Logical Link State Diagram
Figure

)

NSP

State S

(

Page

LEGEND:

contains logical link state consisting of the port states
at both ends
transition

the

link

(Table

2).

caused by NSP

transition caused by a Session Control

call

+++++>

arrow

l‘y

A state from which an exit can be made
potentially unstable state.
A state from which
stable states.

the

A state from which an
+++++> -~ arrow
1s
non-deterministic.

The

logical

1link

only

exits

exit can
a
state

states

are

made
from

presented

disconnection
or abortion of

the

link

----- >

arrows

by
more
which
the

above

are

than
exit

one
1is

describe

the

from the RUN state when

requested by either Session Control
module.
This
1is
true
because
the Session Control requesting a disconnection could
be either the Session Control that requested the loglcal link
or the module that accepted the loglcal link.
If a logical link enters the DI/RUN or RUN/DI
state
because
of
a
disconnect
request
by
one
of
the
Session Control
modules, then an NSP exit from the DI/RUN or RUN/DI states 1is
possible
only if the Session Control module in the RUN state
has provided a
sufficient
number
of receive
buffers
to
receive all
data
transmitted
by the other Session Control
module.
The +++++> arrow exit from either
of
these
states
means

that

NSP

guarantees

to make

exit

this constraint has been met.
Similarly,
the
DI/DI
state
1s
possible
only
1if

eventually

only

Control
modules
sharing
the
1logical
1link
has
met
constraint.
This constraint does not apply when the DI
state 1s entered because of an abort request.

- Figure

Logical

Link State Diagram

an
NSP
exit
from
one of the Session

(continued)

this
port

NOTES

5.0

Page 57

NSP Data Bases and Buffér Pools
NSP DATA BASES AND BUFFER POOLS

This section specifies the variables and parameters in the data bases
|

and buffer pools described in Section 2.2:
o

NSP's internal data base (Section 5.1)
Session Control port data base (Section 5.2)

Resérvéd port data base (Section 5.3)
Node data base (Section 5.4)

Buffer pools (Section 5.5)

5.1

NSP's Internal Data Base

This data base

Network

contains

Management

can

describes the data base.

NSP's

internal

variables

and

parameters.,

modify some of these (Section 3.2).

Table 3

NSP Data Bases5and"BufferTPoolSoYdtfij
o
NSP's

Page 58

Table 3
|
Internal Data Base

+—-——————;—————+——;————~————+——v—++--—++4——-4—6—;—4e—ffe—+—+ ————————— +

Name

NSPstate

Initial

value

|IBit

‘

|width|

Definition

State-'"halted" or runnlng"

}

_I==========================:===================fi====i=fi£==fi=fi==:=====

| "halted"

l—————————————;+——————————+++=a;~;+;
——————————————— T

NSPself

NSP1nact

tim | 0+

Ill6'nl’The node address of thlS NSP

|—-—---—~-—-—-~+*-4—*-“-*—-¥—+*4%+*'
————————————————————————————————— +

|
|

]

|
o

IZNSPs

1nact1v1ty tlme value (in

| = ee

NSPdelay

l system dependent units).
0 means]|
| " no t1me value" (Sectlon 7. 4)
|
e

TT+

|':8_'1;NSP s

"delay factor" (Sect. 6.6) |

"round tr1p delay estlma—

|————————-—————+——; ——————————— o ———— +%—————=—————-~~——~————~—————;
————— +

NSPweight

| NSP's

tion factor” (Section 6.6).

]

l______a___‘g__+a;;; ________ {—a__a+;_¢________-_a_______*_

-_~___;;___+

| NSPretrans

"retransmit threshold"

for

1Zdeterm1n1ng confidence in network|

| (Section 7.5).

| NSP's

connectivity

fora

loglcal

l1nk

|_____+;_____a_+_____a_-__d_+adt_l+;_________-___fi_;gzigg;;;;_;;_

|
|

NSPmax

____+

| *
| The maximum number of ports that
|
| NSPhas had simultaneously in a

| -

|
|

| state other than OPEN.

I_______;;____4+___a__*,__a;+ég;;;+;_______________-__-___;;;; _______ +

NSPversion

4.0

*fvl“NSP s versionnumber.,;d,iy

|___-________-l+__5;;-_-___,+__f€;+g
____________________'_;;i;;_;

| NSPtotal
|

’

lo*

_____ +

*751?The total number of portsNSP canl

| handle simultaneously.

|——-———~——-————+—————a ——————— e pp—— +4———————-—-——————-——~——-=—fi:;a————+

NSPbuf

]

|
|
N

- —— =

NSPtryhard

N
|

|
I
:

|
i
|

to the maximum Routing

Layer block size

[returned from

| Routing Layer Read Blocksize.]

1
|

| minus 13, the maximum NSPheader
| size.
See Sectlon 5.5)

—— - o t———— Fm

| ceiling
|
I
of
|
INSPretrans/Zl

This value

This

| NSP's "tryhard threshold" for
| determining when the tryhard
I'flag should get set (Sect 5.2)

1s not essentlal to the model

is a suggested initial value,

bound to use th1s

1mplementatlon.

1mplementatlons
1n1t1al value.»

are

|
|
:
|

not

5.2

Page 59

NSP Data Bases and Buffer Pools
Session Control Port Data Base

ports.

This data base consists of a collection of

NSP

allocates

port on a Session Control OPEN or CONNECT-XMT call. A port contailns
the minimal information required to maintain a logical link. Table 4
|
specifies a Session Control port.
Table

Session Control Port

——— — fmmm—————— o
o

: Name

| Initial [|Bit
| value

| STATE

fmm

— +
e—
——————

|Width| Definition

Oor CI |

| 0

| NODE

| 16

| Remote node address.

| O

| 16

| Local link address.

| ADDRrem

| 0

| 16

| Remote link address.

| CIRCUIT
|
|
|

| O
|
|
|

| NEXTHOP

| 0

| VERSION

| 0

| TIMERdat
|
|

| O
|

+—-——————————————— t————————— +——————_—_—_———

—_————— — —e
_—————
e
+——————————————— +——_—————— +———— 4+——_—

| ADDRloc

| The state of the port.

— ————
e ——— tm——— e

——

—— — — +

— —+
e ——————

e ————— o

— +
————— f————— e

——— — o
o

————— e o

|
|
|
|

| 16

| Node Number

——T

———— pmm
b

e ———— Fm——— o

fmm

|
|

|
|
|
|

m fmm
————
e
fmmm

| TIMERcon

| 0
|

|
|

%
———t————————

]

— ————— +
—e

| The version of the remote NSP.
e

——————

| Message timer value for Data
| Segment messages.

— pmmm—————— F————— e
————

| O
|
|
|

e
|
|
|

—

|
]
+

Message timer value for
Interrupt or Link Service
messages (data type messages
other than Data Segment).

|
|
|

| Message timer value for Connect
| and Disconnect messages.

|
I

|
|
|
|

e ———— t———— o

e —

——————————— +

——— — fmmm—————— f———— e ——— e fmm e

| Inactivity timer value (Sect. 7.4) |

| TIMERinact

| 0

| NUMdat
|

| 1
I

fmm————— ———————— o———— fm———— e

et
ee

—————

|
|

e ————e +

NSP Data Bases

and Buffer

Pools

Page 60

Table 4 (Cont.)
Session Control Port
———————
e
————— +

Initial

|Bit

Value

|IWwidth]|

|
I
I

I
.
|

Service message
type

messages

transmit

other

than

(data

Data

————————— +-————+

I
|

Segment

message

available

from

Session Control.

—_————————— +—-———- +

Number of highest numbered Data
Segment

message

sent

local

NSP.

————————— +-————+

————————— +-—————+

I
I

ACKrcv dat
+ _______________

FLOWloc dat

|
I

]
I

—

- —_——_——_—————

FLOWrem 1int

sent

Number

last

the

message

from

Interrupt

Link

acknowledgment

local

NSP.

highest Data

acknowledgment

remote

NSP.

Segment
received

I
|

The

normal

will

data
sent in

request

the

count

that

Data

Request message.

The

I
I
|
|
I
|
I

————————— t—————

|
$+——_

Service message

————————— +—————t e %

| |
I
|
|
I
I
FLOWrem_dat

Number

————————— t=—————t

FLOWloc int

e
e
T
——

last Data Segment message |
acknowledgment sent by local NSP.
|

————————— +————=+ ____________________________________ -+

I
I
e
S
——

Number of

flow

control

state

for

receiv-

One

of:

ing interrupt data.
This variable
takes into account the contents of
the buffer BUFrcv as well as
whether or not a new interrupt request

should

sent.

"interrupt"”
"send request"
____________________________

________

The cumulative normal data request
count

received

from

the

remote

NSP.

————————— +————— ———————————————————————————————————— +

I
I

|
I

————————— +———— +

The cumulative interrupt data
request count received from the
remote

NSP,

NSP Data Bases and Buffer Pools
Table 4

Page 61

(Cont.)

Session Control Port

—— +
—————— e
e ———— t————— e
——— pmmm
fmm e

| Name

| Initial IBit

|Wwidth| Definition

| Value

I==============:=====================================================I

| FLOWrem sw

I
|
|

| "send”

|
|
|

I
|
|

| The normal data on/off switch most |

| recently received from the remote
|
"send"
| NSP. One of:
"do not send"
I

|
|
I

|
|
|
|

The flow control type of the
|
remote receiver (determines
how remote normal data request
counts are interpreted). One of:

|
I
|
|

"session-control-message”

——————— fmmm—————— f————— e —————— +

| FLOWrem typ
|
I
|
|
I

| "none"
|
|
|

|
|
|
I

N
|

—————

| FLAGoth ack

I
I

"none"
"segment”

I
|

|
I

e ———— fm——— o —————— +

———— pmm
o

| FLAGdat ack

| false
|

| false

I requ1red" flag.

fomm—————— m———— i

| Boolean "data acknowledgment

— — — ———————_—— +

: Boolean "other data acknowledgment |

| required" flag.

| Boolean "buffer required for con-

b ————— $———— e +
————
emmm
fmm

| FLAGbuf

| false

e ———— b —————— tm——— e +

| FLAGint avail | false
|

———— b
e

———— fmm
o

|
|

| BUFxmt

|
|

I avallable flag.

——— bm———— e - +

|1
|
|

| Boolean "transmit allocation
| requested for the port connect/
I dlsconnect transmit process."

]
I
-

|
|

| Boolean "transmit allocation

| requested for the port
| data transmit process."

| 0

I
|

| Buffer to contain data for trans-

| Initiate, or Interrupt messages.

| Buffer to contain data for

|bytes| mitted Connect Confirm, Disconnect |

—— }
———— pm———— o

|bytes| received Disconnect Initiate
| or Interrupt messages.
|

—————
——— frmmm—————— Fm———— e
o

| BUFacc
|

| Boolean "transmit interrupt data

—————
————— b —————— pm———— e

o
—
e

| BUFrcv

———— T s et +

| FLAGdat alloc | false

|
|

| 0
|

I
I

——— fmmmm————— f————— e
fmm e

NSP

Data

Bases

and

Buffer

Pools

Table 4 (Cont.)
Session Control Port

| Initial |Bit

Name

BUFcon

value

0's

N
|

|Width

l
N

| data from a transmitted
or
| received Connect Initiate message.

e o —————— e + ____________________________________ + |

BUFsrc

0's

|
|

Address of a buffer to contain

|
|

source

e e ——————— +———== +

COUNTretrans

| O

node

received

address

connect

for

request.

____________________________

________

Count
of message

retransmissions.

o ————— +———— +

DELAYstr tim

Round trip time-of-day value for
start of round trip time estimation]|

R i o —————— $————— +

DELAYmsg
num

|
N

I
I

The

number

the

Data

Segment

single

"Other

| message currently being timed for
| the round trip delay estimation.

+-———_—_——
e ———
—_—_—— +-————————t——_—_—— +

OTHERstate

"ready"

|
|
|
+-————————

OTHERtyp

|
|
|

——_————— +-——— +

|
A
|
|
|
|

I
|
|
|
|
|

}

true

state

the

message

any.

One

being

transmitted,

of:

"ready"
14 Sent "

"timeout"
________________________

____________

The

|
|
|
|
|
|

Rt e ——— ———— +

CONFIDENCE

The

Data"

type

"Other

being sent,
only when
"ready".

Data"

any.

OTHERstate

One

message

has meaning]|

not

of:

"interrupt"
|
"interrupt request"”
"data request"”

____________________

________________

The Boolean "confidence" variable

for

the

port.

e mm——————— - +

SIZEseg

TRYHARD

{

16 |

T Ty
—— t———— +

false

}
the

This value

_________ e

1s
e

not

port.

SEENG

GNN MER GUNN

R
GNED

GED
G

S
SR

SN
WD

GO
MY

G
SSUVR

GRS

SES

CHME

eein

GEED

NS
G

GWER

SRl

CHNEL

SURD

CMAR

—

——

—

cmmm

mme

e
S

essential

—

———_———

—

NSP Data Bases and“Buffer Pools
5.3

Page 63

Reserved Port Data Base

This data base conta1ns a collectlon of port
varlables
reserved
for
NSP's
1internal wuse.
NSP
wuses them to manage responses to received
messages that do not map onto the Session
Control
port
data
base.

Table
5 describes a reserved port.

Table5

Reserved Port
o

————— e

————— o ————— T
L
T T pp—— +

I
] In1t1al
| value
=
| Name

|
|

Bit
|
:
| Definition
Width

I
|

|===::::::::::2;;;::;;;;::::==;:fi=:=======================fi==========l

NODE

ee
m

ADDRtmp

| 0

Remote node address.

Temporary

(1ocal)

llnk address.

b
b
e+

ADDRrem

116

I-Remote

llnk address.

b
e

|
|
|
|
|

MSGtype
-

|
|
|
|

| "none"
|
|
I
I
l

——————

CIRCUIT

| 2
|
|
|
|

fm———————— Fm——————— e e +

|
|
|
o

N
|
|
|

I-The

NEXTHOP

|10

c1rcu1t

number

e et

Node Number

t——_——————————— —-—+-——————= +-—————— =t

5.4

to use

| transmit messages to Routlng
| One of:
|0 (="unspecified")
l
‘a circuit number

T
s st

|
|
|
|

—— +

|
e ———————— +

Node Data Base

The node data base contains a collection of node descriptors.
A
node
descriptor
1is 'a collection of node-dependent variables and counters.
These are required in processing logical link connections.
When
NSP

receives

elther an outgolng

an incoming connect request

connect request

(via

Connect

(from Session Control)

Initiate

message)

NSP

attempts to allocate a node descriptor for the remote node if one does
not exist.
Failure of such an attempt has the
same - conseguences
as
failure to allocate a port
Table 6 descrlbes a node descrlptor.

NSP Data Bases and Buffer Pools
-~

|
Table

Page 64

Node Descriptor

——————— e ——————— e

Name

NODEaddr

Initial

| value

Bit

| width

Definition

Node address.

I==:===========================:=====:==================:===:========

e ———— fmm

NODEdelay

e ————— e ———— o

Estimated round trip delay.

+-—-———————————————t—_—_—————— +-——————— +-————— e,
——— +

|
|
|

NODEactive

|
|
|

The number of ports with

logical links to the remote
node in a state other than
|
OPEN,

|
|
|

———————— +-———————— +-——————— +--—————
e ——————

NODEbyt rcv

Total user data bytes received.

e fm——————— fmm

e ———— e +

|
|

NODEbyt xmt
|

|
|

e pom

NODEmsg_rcv

|
|

e ———— fom

NODEmsg_ xmt

|
|

T
T T

e ——————— e

Total user data bytes
transmitted.

Total NSP messages received

Total NSP messages transmitted.

t+-———— —_—————————— +-—-——————— +-—————— +- — — — — e
———— +

NODEcon_rcv

|
|

NODEcon xmt = |
|
N

Connect Initiate messages

———————— fmmm—————— b S

|
|

|
|
I

o ——————— ————e
e b

| NODEcon_rej
|
|

|
|
|

it &

|
|

Connect Initiate messages
transmitted.
|

|
|
|

Connect Initiate messages
received for which there was no
OPEN port.

A e

received.

o
|

o o ————— b ———— o

NODEt imeout

5.5

Buffer

{

Number of timeouts causing NSP

message retransmission.

|
|
|
+

Pools

There can be up to six bfiffer pools, asfollows:
Large transmit buffer pool.
Large transmit buffers
are
required
to
transmit
Connect
1Initiate
or Data Segment messages.
The form these
buffers
take
1s
1implementation-dependent.
Implementations
that
support
buffer
chaining
may
require
only
enough space in a large
"transmit buffer to build a message header.
Other implementations
may

NSP Data Bases and Buffer Pools

Page 65

use buffers no larger than
the size Routing can transmit.
size

for the pool

1s one buffer.

The minimum

Small transmit buffer pool.
Small transmit buffers
are
required
to
transmit
messages
other
than Connect Initiate or Data Segment.
The
minimum size for this pool is one buffer.
An implementation may use
a
single
transmit
buffer
pool.
1In this case, the buffers must all be
"large."

—

Receive buffer pool.
Receive buffers are required to receive
an
NSP
message from Routing.
Minimum buffer size is 230 bytes.
This size is
equal to the contents of NSPbuf (Table 3, Section 5.1)
plus
13
(the
maximum
length
of
a
Data
Segment
header).
All NSP messages are
received into buffers of the same size.
The
minimum
size
for
this
pool

is one buffer.

Commit buffer pool.
Once data is
placed
1in
a
receiving
node 1s committed to keeping it.
Such
to the transmitter.
A commit buffer is the same
buffer.
This buffer pool is not required for the
NSP.

commit
buffer,
the
data is acknowledged
size
as
a
receive
correct operation of

Cache buffer pool.

Cache buffers hold received Data Segment

messages

that
cannot
be acknowledged either because they were received out of
order
or because there is no permanent
storage
(such
as
a
commit
buffer
or
a Session Control buffer) for them.
A cache buffer is the
same size as a receive buffer.
This buffer pool is not
required
for
the

correct operation of NSP.

Event buffer pool.
This contains buffers for NSP's
event
queue
for
reading
by
Network Management.
The minimum size for the pool is one
buffer.
|

6.0

DETAILED FUNCTIONAL MODEL

Section 6 is essentially a model implementation of
NSP that
defines
the operation
of NSP in terms of a high level language.
There 1s no

requirement that
an
actual
implementation
conform
to
either
the
structure
or the logical flow of this model.
This is a specification
of function only.
The following variables are used in the model:

o Data base variables from Section 5.
capital
and
small
letters
CONFIDENCE, CIRCUIT and NEXTHOP.

plus

These are given in
STATE,

TIME. This referS'to the value of a local

keeps

Fields in a message from
Section
8.
These
variables and are given in capital letters.

all

other

All NSP segment number arithmetic in this section is performed

modulo

the time of day.

segment

number

clock

mixed

VERSION,

that

4096.

NODE,

are

1is defined to be greater than a segment

Detailed Functional Model
number m

if 0

(n - m)

|
2048,

Page 66

modulo 4096.

A timer is modeled as a variable in a port.
A
timer
1is
1in
one
of
three
states:
stopped, running, or expired.
A timer contains a zero

when it is stopped, a time value (the expiration
time)
greater
than
the
time
of
day
when
it is running, and a time value less than or
equal to the time of day when it has expired.
|
This

section does

o
o

not describe:

The operation of the Network Management interface,
The maintenance of counters in the

variable NSPmax

in NSP's

node

data

internal data base,

The handling of NSP'S event queue, or

The handling of port pools.

base

and

the

It is assumed that the above operations are described sufficiently

the description of

the Network Management

interface

in Section

1in

Finally, this section does
not
describe
the
operation
of
an NSP
implementation
that requests no flow control
or message flow control.
Nor does it describe the operation
that
would
generate
a
negative
acknowledgment
or
exercise
"on/off" flow control.
The operation of
NSP in transmitting to an NSP implementation
that
uses
these
other
forms
of
flow
control
and acknowledgment
1is described in Section
2.6.3.

The colloquial language in.the model adheres to the following rules:

1,
2.

<-- is the aSsignment operator
< > means

"not equal

to"

<= means "less than or equal to"

>= means

"Loop...Endloop" defines a section
of
1logic
repeatedly.
An
"Exitloop"
causes
an
exit
immediately following the "Endloop."
|

"If...Elseif...Else...Endif" defines a collection of separate
logic
sections,
each guarded by a Boolean condition.
After
the first section with a "true" Boolean guard is executed, an
exit
1s made to the logic following the "Endif." The implied
Boolean condition on "Else" 1s "true." That is,
the
section
following
an "Else" 1s always executed if a previous section
has not been executed.
|

"greater

than

equal to"

that
executes
to the logic
|

7. Comments are near the code to which they apply, either before
or after.

‘Detailed Functional Model
6.1

Page 67

Interface Routines

This section specifies how

NSP

handles

the

Session

Control

calls

Control

port

described
in
Section 3.1.
The operation is described by a series of
algorithms with comments.
The algorithms assume that at each of
the
entry
points
1involving
a port identifier passed by Session Control,
NSP does the following:

Checks the port

identifier

for validity.

Maps
the
port 1identifier
descriptor, if possible.

onto

Session

" The port descriptor variables used herein refer
to those
descriptor.

in the proper

OPEN:

Logical
If

link address assignment

(NSPstate =
return

"halted")

"no port

(Appendix A)

then

allocated

NSP

halted"”

Elseif

(Session Control port 1is available
and a logical link address is assignable)
allocate Session Control port

then

ADDRloc <-- assigned link address
STATE <-- "O"
|
BUFcon <-- Session Control's buffer descriptor
'BUFsrc <-- address of "source" argument
return "port allocated" with port identifier
Else

return

‘

"port

not

allocated -

insufficient

resources"”

Endif

CLOSE:

Logical link address‘deassignment'(Appendix A)
deassign
release

link address

1n ADDRIloc

resources

CONF IDENCE :
If

(STATE =
return

"RUN"

Else

return
Endif

return

"CC"

"DR"

STATE

in
|

invalid state"
|

or
|

"port

STATE:

)

CONFIDENCE

"DI")
|

then
|

Detailed Functional Model

Page 68

CONNECT-XMT
:

Logical link address assignment (Appendix A).
Setting
FLAGbuf
true
causes
the
connect/disconnect process for the port to send a Connect
Initiate message.
NSP passes the circuit, nexthop value to Routing for
subsequent transmissions for this port.
The circuit,nexthop value 1s
|

used for loop-back testing.

(NSPstate = "halted") then
return "no port allocated - NSP halted”
Elseif (Session Control port
1is availlable
and a node descriptor exists or 1s avallable
If

and a logical link address is assignable) then
allocate Session Control port descriptor
allocate and initialize a node descriptor, 1if necessary
-

NODErem <-- destination from call
ADDRloc <-- assigned link address
STATE <-- "CI"

BUFcon <-- Session Control's buffer descriptor
CIRCUIT <-- circuit from call
NEXTHOP <-- nexthop from call
FLAGbuf <--

true

return "port allocated" w1th port

Else

return "port not allocated -

identifier

1nsuff1c1ent resources”

Endif
CONNECT-STATUS:

Accept or reject data 1S only available if the port is 1in the "RJ"

"RUN"
states.
The
data
1is
in
BUFacc if the port 1s in the "RUN"
state;
the data is in BUFrcv if
the
port
1s
1in
the "RJ"
state.
Furthermore,
since
BUFrcv
receives
interrupt data once the logical
link is running, Session Control can obtain
accept
data
only
once.
The variable FLOWloc int identifies the contents of the BUFrcv buffer.
Setting this variable to "empty" allows NSP to receive interrupt
data
|
|
on the logical link.
(STATE = "RJ") then
"Session Control's buffert <-— BUFrcv
return "connect request rejected"
Elseif (STATE = "RUN") then
If (FLOWloc int = "accept") then
Session Control's buffer <-- BUFacc
If

Endif

return

Else

"connect

return "port not

Endif

request

accepted”

1in RUNNING or REJECTED state"

Detailed Functional Model

Page 69

'ACCEPT:

Setting 'FLAGbuf

true

will

cause

the connect/disconnect

process to send a Connect Confirm message.
If

(STATE =

"CR")

transmit

then

STATE <-- "CC"
BUFxmt <—-- Session Control' s data
FLAGbuf <-- true
return "link accepted”
Else

~return

"port not

in CONNECT-RECEIVED state"

Endif
:
REJECT

Settlng FLAGbuf true causes the connect/dlsconnect transmit process to
send a Disconnect
If

(STATE =

Initiate message.

"CR")

then

STATE <-- "DR"
BUFxmt <-- Session Control's
FLAGbuf <-- true

data

return
"link rejected”
Else

return

Endif

"port not

i1n CONNECTRECEIVED state”

DISCONNECT—XMT:

Setting FLAGbuf false and STATE to "DI" causes the connect/disconnect
transmit process
to send a Disconnect Initiate message only 1if there
are no outstandlng,'unacknowledged data messages.

(STATE =

"RUN")

then

STATE <-- "DI"
|
BUFxmt <-- Session Control's data
DELAYstr tim <-- 0
FLAGbuf <-- false
return "call accepted"
Else

‘return
Endif

"port

not

in RUNNING state"

Detailed Functional Model

Page 70

ABORT-XMT:

This routine acts

routine

DISCONNECT-XMT ~except

that it

~NUMhigh to ACKrcv_dat to stop the transmission of data messages
allow the transmission of a Disconnect Initiate message.

(STATE =
STATE

"RUN")

<--

sets

and

then

"DI"

BUFxmt <-- session
DELAYstim
r <-- 0

,
control's

data

stop timer TIMERdat
stop timer TIMERoth
FLAGbuf <-NUMhigh <--

false
ACKrcv_dat

return
Else

"call

accepted”

return

"port

|
not

Endif

RUNNING

state"

DISCONNECT-RCV:

The

connect/disconnect

process

places

any

BUFrcv.

(STATE = "DN") then
If (BUFrcv empty) then
return
Else

"no

disconnect
|

received disconnect

|
data

available"

Session Control's buffer <-- BUFrcv
return "disconnect data available"
Endif
Else

return

"port

not

Endif

|
|
|
DISCONNECT-NOTIFICATION
state"

DATA—XMT:

The

segmentation

(STATE =

pass
pass
Else

module

"RUN")

handles

this

call

almost

entirely.

then

call

to segmentation module
return to Session Control

return

"port

Endif

not

RUNNING

state"

XMT-POLL:

The

segmentation module

handles

this

pass call to segmentation module

pass

return

Session

Control

call

entirely.

data
|

Detailed Functional Model

Page 71

DATA-RCV:

The reassembly module handles this call almost entirely. This call is
accepted in the DI state (Section 4.1) to preventa Session Control
|

deadlock.

If (STATE = "RUN",

"DI" or "DN") then

pass call to reassembly module
pass return to Session Control

Else

return "port not in RUNNING or DISCONNECT-INITIATE state"

Endif

RCV-POLL:

The reassembly module handles this call entirely.
pass call to reassembly module
pass return to Session Control
INTERRUPT-XMT:

The
BUFxmt is the single buffer holding outgoing 1interrupt data.
When
buffer.
the
of
state
variable FLAGint avail indicates the
Putting
FLAGint avail is ~false, then there is no data in it.
data
the
causes
true
to
vail
interrupt data in it and setting FLAGint_a
transmit process to send an Interrupt message.
If

(STATE < > RUN) then

return "port not in RUNNING state"
Elseif (FLAGint avail false) then
BUFxmt <-- Session Control's data
true
return "data accepted”

FLAGint avall <--

Else

return "data not accepted - insufficient resources”

Endif

Detailed Functional Model

Page

INTERRUPT-RCV:

The data receive process
FLOWloc_int
=
T"empty."

places received interrupt data in
BUFrcv
if
The receive data process informs this routine
that
interrupt
data
1is available
by
setting
FLOWloc int
to
"interrupt."s This routine
informs
the data transmit process that it
should request another interrupt message
by
setting
FLOWloc int
to
"send
request.
This
causes
the
data
transmit process to send an
Interrupt

Request

(STATE <
return

message.

> RUN)

"port

then

not

RUNNING

state"

Elseif (FLOWloc int = "interrupt") then
Session Control’ s buffer <-- BUFrcv
FLOWloc int <-- "send request"
~
return "data returned"”
Else

return

"no

data

returned"

Endif

6.2

Receive

Dispatcher Module

This module has
Routing,
polls
-

processes.

an imbedded process
that
gives
receive
buffers
to
to
get them back, and then glves them to the receive

Although

not

exp11c1tly

algorithms,
these processes return
dispatcher module after the buffers

modeled

1in

the

receive

the receive buffers to
have been processed.

process

the

receive

The receive dispatcher module maps received messages
onto
ports
parses
messages into ‘field contents.
Mapping a received message
a particular port is described below.
|
|
1.

If the TYPE or SUBTYPE subfields of
reserved
binary
values, or if the
then discard the message.

Discard

MSGFLG

field

contain

extended,

received No Operation message.

A received Connect Initiate message or Retransmitted

the

MSGFLG

and
onto

Connect

Initiate
message
with
DSTADDR
=
0
maps onto any Session
Control port with node = NODE, ADDRrem
= SRCADDR and STATE <>
"O"
or
any Session Control port with STATE = "O", if such a
port exists and if a node descriptor exists or can be created
for
the
source
node.
Otherwise, it maps onto any reserved
port with MSGtyp = "none", if such a port exists.
Otherwise,
discard the message.
A

returned Connect

Initiate

message

Retransmltted

Connect

Initiate maps onto the Session Control port with STATE = "CI"
and SRCADDR=ADDRloc,
if
such
a port
exists.
Otherwise,
distard the message.
|

Detailed Functional Model

Page 73

Resource

Treat a received Disconnect Confirm message as a No

a 1, as a Disconnect
the REASON field contains
if
message
a 42, and as a
contains
field
REASON
the
if
message
Complete
|
4l.
a
contains
field
REASON
the
if
message
Link
No

s onto a Session Control port in the
map
The following message
node = NODE and DSTADDR = ADDRloc,
source
the
with
state
"CI"
messages, with the exception of
These
exists.
port
a
such
if
also map onto a port in
message,
ent
Acknowledgm
Connect
the
any other state with source node = NODE, DSTADDR = ADDRloc,
and SRCADDR = ADDRrem, if such a port exists.
.00 0O0O0

Connect Acknowledgment
No

Resources

Connect Confirm
Disconnect Initiate

Disconnect Confirm with REASON < >

41, or 42

If a Connect Acknowledgment or No Resources message cannot be
If a Connect
mapped onto a Session Control port, discard it.
Confirm or Disconnect Initiate message cannot be mapped onto

a Session Control port, map
MSGtyp = "none," if one exists.

it onto a reserved port with
Otherwise, discard 1it.

The following messages map onto a Session Control
source

the

port

with

node=NODE, DSTADDR=ADDRloc, and SRCADDR=ADDRrem,

if such a port exists.

O0O0O000O0O0

Disconnect Complete
No Link
Data

Segment

Data Acknowledgment
Interrupt

Data

Request

Interrupt

Request

Other-Data Acknowledgment

Interrupt, Data Request, or Interrupt Request

A Data Segment,

message that cannot map onto a Session Control port 1is mapped
onto a reserved port with MSGtyp = "none," if one exists;
Discard the remaining messages
1is discarded.
it
otherwise,
in the above list if they cannot map onto a Session Control
port.

"CI,"
Note that a Session Control port with STATE = "Oo,"
for
value
"CD," "NR," or "NC" does not have a defined
such
onto
ADDRrem. Therefore, NSP cannot map these messages
a

port.

Detailed Functional Model

Parsing messages into field
The

following
1.

are

special

contents

rules:

~ Page 74
generally

straightforward.
|

Check the QUAL fields of a received Data Segment, Interrupt,
Link
Service,
Data Acknowledgment, or Other Acknowledgment
message to determine if
the
fields
are
wvalid.
Ignore
a

' NUMBER field
Mask

Link

the

SEGNUM

Service,

message

regardless
Mask

the

the QUAL

field has

field of

Data
low

received

Data

Acknowledgment,

order

bits.

invalid value.
Segment,

or Other

Ignore

the

Interrupt,

Acknowledgment
wupper

Dbits

setting.

the LSFLAGS field of a received Link Service message
to
the
low order 4 bits.
Ignore the upper 4 bits regardless of
setting.
Check the reserved values of the FCVAL INT
and
FC
MOD subfields of the LSFLAGS field, however.
If the reserved
values are used, ignore the entire Link Service message.

Detailed Functional Model

Page 75

Index to Routines

6.3

than
Sections 6.4 through 6.9 contain routines that are used in more
your
aid
To
once.
defined
only
are
routines
These
one subsection.
reading of the model, Table
7
1is
an
alphabetic
1list
of all
the
routines used in these sections.
The table shows both the section
1in
which the routine is defined and the section(s) that call or otherwise
use

the

routine.

Table

Index to Routines Used 1in Model
— —_— e
- —— — +

Routine

| ACK-SESSION-CONTROL

Defined In

6.7

6.9

—— —_————————— —_—tm

ALLOCATE

| Used In

6.6.2

6.6.1,

e
———— +

e
— e
—— e
——— +

CHECK-ALLOCATE

6.9

6.6.1,

- —————— e - e
— — +

| COMMIT-NUMBER

6.5

6.4.2

6.6.2

—— ———————— e ———— tem— e
——— tm—————————————— +

| DATA-ACK-SENT

e
— e
——— e
— -+

| DATA-ACK-TO-BE-SENT

-e
—— — e
———— +

DATA-REQUEST-TO-BE-SENT

-e

| DATA-TO-BE-SENT

- ——————e

DEALLOCATE

6.6.2

6.9

e e

| GET-SEGMENT

6.6.2

6.6.1, 2,

ee
———— +

e
———— +

6.8

e b be
——— +

6.6.2

— — —e
— —e
——— +

INTERRUPT-TO-BE-SENT

INT-REQUEST-TO-BE-SENT

6.6.2

t——— e
— e

— —+

— — — $———— ————————————— —t e
——— +

| LAST

6.8

6.6.2

| MESSAGE-SENT

6.6.2

6.8

6.4.2,

6.6.2

| OTHER-DATA-ACK-TO-BE-SENT

6.6.2

| OTHER-DATA-SENT

6.6.2

| PROCESS-DATA-ACK

6.4.2

ee
— +
—e
——— e ————————— +

| MESSAGE-TO-BE-SENT

—

e
— t——————————————— +

6.6.2

————— e ———————————— e e
——— +

| OTHER-ACK-SENT

+—-———- aunhee ettt +-———————_———_———————— +-—————————————— +
f—— e
— -e+

s —_——————ee e e
—— +
+— — _—_— e
— —- —e
——— +

Detailed Functional Model

Index

Page

Table 7 (Cont.)
Routines Used

in Model

e e

Routine

| Defined

PROCESS-OTHER-DATA-ACK

Used

6.4.2

e e
e e

| REALLOCATE

e e e

e e

i e

o e

e e

6.9

6.7

6.4.2

6.6.1,

e -

SEND-CONNECT-ACKNOWLEDGMENT

+———————— e

+ —F — F — f —F — o — f —f — o o p — o — o — p — f — o — p — f — o — o — f — f — o —

6.6.1

e
-e +

SEND-CONNECT-CONFIRM

6.7

6.6.1

ee e e e +

SEND-CONNECT-INITIATE

6.7

6.6.1

+—"—————"——"——__—"——-— ——————————— + —————————————————————————————————— +

SEND-DATA-ACK

6.7

— - ———————————— e
et

SEND-DATA-REQUEST

6.7

6.6.2

e +

6.6.2

+——-————————-——————————————_— ——————— +-———————— e
—— ———————— +

+'.._..____.__.'. _________________________ ———

SEND-DATA-SEGMENT

6.7

SEND-DISCONNECT-COMPLETE

6.7

ee e

SEND-DISCONNECT-INITIATE

SEND-INTERRUPT

——————

6.7
e

— e

6.6.2

o —— e
—+

6.6.1

I
+

6.6.1

e e

6.7

6.6.2

-e
Tt
b+

SEND-INTERRUPT-REQUEST

6.7

6.6.2

e e
e
+

SEND-NO-LINK

SEND-NO-RESOURCES

6.7
e

e e

6.6.3

e e+

6.7

6.6.3

R it e
-+

SEND-OTHER-DATA-ACK

6.7

SEND-SMALL-MESSAGE

6.7

6.6.2

|
+

6.7

e t—————— e
— e
e e
+

SET-SWITCH-AND-FLAG

6.4.2

e
e
e
e e e
e
e +

SPECULATE-NUMBER

6.5

6.4.2

e
e
e
e +

STORE-SEGMENT

6.5

6.4.2

e-e
e e
e

TIMEOUT

ROUTING-TRANSMIT

6.6.2

6.6.1,

+—————¥-———-" ——————————————————————— +— — — —r e,
e, ——— +

3.3

e ————————— e

UPDATE-DELAY
e

GENEy

]
D

CEL

GEp

GHAE

GEMN

GhNE

e—

+ S AELG SRR

6.4.2
GG

GRS

GMENR

SRS

GhEN

WAL

MIEE

SEmh

SullE

GLER

GLw

6.7

6.4.1,

Page 77

Detailed Functional Model
Receive Processes

6.4

This section contains algorithms for implementing
|

processes:

the

three

Connect/Disconnect Receive Process (Section 6.4.1)

Data Receive Process (Section 6.4.2)

Reserved Receive Process (Section 6.4.3)

receive

6.4.1 Connect/Disconnect Receive Processes - These processes receive
messages from the receive dispatcher module. The message variables
below refer to the information content of message fields as returned
from the receive dispatcher module. There is one connect/disconnect
|

receive process for each Session Control port.

Loop

This process loops forever.

Oncase (received message type)
When this process receives a message,
4

statement.

execute

the

case

appropriate

Case (Connect Acknowledgment)

If this message is received when the link is in the "CI" state, then
observe the round trip delay (Section 7.3). This value 1s equal to
the current time of day minus the time the Connect Initiate message
Routine
This latter time 1is kept 1in DELAYstr tim.
was sent.
variable
the
updates
UPDATE-DELAY makes this calculation and
NODEdelay.

1f (STATE = "CI") then
STATE <--

"CD"

Call UPDATE-DELAY
Endif

Case (Connect Initiate or Retransmitted Connect Initiate)
A Connect Initiate message may contain any value in the INFO field.
the SERVICES field must contain "none,” "segment" or
However,
connect/disconnect
the
Setting FLAGbuf true causes
"message".
transmit process to send a Connect Acknowledgment message.

Detailed Functional Model
If

(STATE =

"O")

Page
78

then

(SERVICES = "none,"

"segment,"

"message")

then

buffer whose descriptor is in BUFcon <-- DATA-CTL
NODE <-- node from Routing
location whose address is in BUFsrc <-- NODE
ADDRrem

<--

SRCADDR

FLOWrem typ

<--

VERSION <--

INFO

SIZEseg

<-- min

FLAGbuf
STATE

SERVICES

<--

(NODE

buffer

true

(SEGSIZE,
minus

the

size of

maximum NSP

large

transmit

header

size)

"CR"

NSPself)

CIRCUIT <-NEXTHOP <-Else

CIRCUIT
Endif

<--

then

CIRCUIT received
NEXTHOP received

from
from

Routing
Routing

|
N
"unspecified"
|

Endif
Elseif
Elseif

(STATE
(STATE

"CR", "CC", or "DR") then FLAGbuf <-"RUN", "CD", or "DI") then discard.
was

duplicate.

Message

true

Case ("returned to
Connect Initiate)

sender"

Connect

In1t1ate or Retransmitted

If (STATE = "CI") then STATE <-- "NC"

Else discard

Detailed Functional Model
Case

Pagé 79

(Connect Confirm)

The testing of INFO and SERVICES is the same
for
a Connect
Confirm
message
as
for
a Connect
Initiate message.
Setting the variable
FLOWloc int to "accept" informs the interface routines that
there
1s
accept data
available.
Since the "RUN" state can be entered, start
the inactivity timer (Section 7.4).
Call UPDATE-DELAY
for
the
same
reasons as when a Connect Acknowledgment message 1s received.
If

(SERVICES

"none,"

(STATE

"CI"

ADDRrem

"segment," or "message")

"CD")

<-FLOWrem typ

SRCADDR

VERSION <--

INFO

<--

then

<--

DATA-CTL

size of a large transmit

TIMERinact <-- TIME + NSPinact

(STATE = "CI")

STATE <-Endif

(STATE =

"RUN"

"RUN")

FLAGdat ack
Endif

then

SERVICES

SIZEseg <-- min of (SEGSIZE,
<
buffer -13)
BUFacc

tim

then Call UPDATE-DELAY

then

<--

true

Endif
Case

(Disconnect

Initiate)

In all cases below, setting FLAGbuf true causes the connect/disconnect

transmit process

to send
a Disconnect Complete message.

If (STATE = "CI" or "CD") then
A Disconnect Initiate message received
in either of these
indicates

rejection

message.

‘

ADDRrem

<--

(STATE =

Elself

"CI")

BUFrcv
BUFrcv

<-- -REASON.
<-- DATA-CTL

then Call UPDATE-DELAY

<-- "RJ"

(STATE =

SRCADDR

first two bytes of
remaining bytes of
FLAGbuf <-- true
STATE

two .states

a previously transmitted Connect Initiate

"RJ")

then

A Disconnect Initiate message received in this state 1s assumed to
be
a
duplicate
caused
by
the retransmission
of
the
message
that
originally caused the transition to the
FLAGbuf

Elseif

<--

(STATE =

true

"RUN")

A Disconnect Initiate message
disconnect of

running

link.

"RJ"

state.

this

then

received
|

state indicates

Detailed Functional Model

first two bytes
of BUFrcv
remaining bytes of BUFrcv
FLAGbuf
STATE

<--

<-<--

Page

REASON
DATA-CTL

true

"DN"

DELAYstr tim <-- (
stop timer TIMERdat
stop timer TIMERoth
Elseif (STATE
= "DIC" or

"DI")

then

A Disconnect Initiate message received in either of these
states
is
assumed
to be a result of a disconnect collision.
In the case of the
"DIC" state, this message may have been delayed in Routing until after
the
reception
of
the
Disconnect
Complete
message that caused the
transition to the "DIC" state.
In the case of the "DI"
state,
there
has
Dbeen
a
crossing of Disconnect Initiate messages in Routing.
In
either case, the response is the same.
FLAGbuf
STATE

<--

true
"DIC"

DELAYstr tim <-- 0
~
Stop timer TIMERcon
Elseif (STATE = "DN") then
A Disconnect Initiate message received in this state is
a
duplicate
caused
by
the
retransmission
of
the
originally caused the transition to the "DN" state.
FLAGbuf

Endif

Case

<--

assumed to
be
message
that
-

true

(No Resources)
I

(STATE =
STATE

Call
Endif

Case

<--

"CI")

then

"NR"

UPDATE-DELAY

(Disconnect Complete)

Stopping timer TIMERcon prevents the
Initiate message after a timeout.

(STATE = "DR" or "DI")
stop timer TIMERcon
stop timer TIMERdat
stop timer TIMERoth
Call UPDATE-DELAY
Endif
:
|

If
If

Case
Stopping

(STATE =
(STATE =

"DR")
"DI")

retransmission

then

then STATE <-then STATE <--

"DRC"
"DIC"

(No Link)
the timers prevents

any

retransmissions.

Disconnect

Detailed Functional Model
If

(STATE = "CC,"

"RUN,"

stop timer TIMERcon
stop timer TIMERdat
~ stop timer TIMERoth
STATE <-- "CN"
Endif

Case

"DR" or

|
"DI")
-

Page 81

then

(Disconnect Confirm)

This case is included only for compatibility with version 3.1.
This
case
occurs
when
a
3.1
system
sends
thils
message rather than a
Disconnect Initiate message for
a
Session
Control
rejection
of
a
Connect
Initiate message.
It
also
occurs when an NSP version 3.1
system receives a message 1n error.
|
If

(STATE =

"CI")

first two bytes
STATE <-- "RJ"

then
of

|
BUFrcv <-|

CALL UPDATE_DELAY
|
Elseif (STATE = "CC" or STATE =

stop timer TIMERcon
stop timer TIMERdat
stop timer TIMERoth
STATE <-- "CN"
Endif

REASON -

.
"RUN") then

Endcase
Endloop

6.4.2
Data Receive Processes - These processes receive messages
from
the
receive
dispatcher module.
The message variables below refer to
the information content of message fields as returned from the receive
dispatcher
module.
There
1is
one Session Control port data receive
process

for

each Session Control port.

Loop

This

process

loops

[(STATE =

forever.

"CC"

"RUN")

(STATE = "DI" and NUMhigh < > ACKrcv_dat)]

then

This process only runs for ports in the "CC," "RUN," or
"DI"
states.
It
runs
for ports
in the "CC" state to receive any data type message

)

as defined by the case statements since the reception of these message
types
will
cause a transition to the "RUN" state.
It runs for ports
in the "RUN" state to receive normal data,
interrupts,
Link
Service
‘messages,
and acknowledgments.
It runs for ports in the "DI" state to
receive data while there
is outstanding,
unacknowledged,
transmitted
data.
This latter case is true when NUMhigh < > ACKrcv_dat.

Detailed Functional

Model

(FLOWloc _dat

FLOWloc dat

contains

retransmitted

the

- Request message can
value to be sent in

Call

value,

be sent.
the next

any,

currently being

The
Data

routine
Request

the

(returned value <

sent,

ACKxmt_dat
Data

returns

the

"false")

pfeviously_

either

commit

COMMIT
-NUMBER

returned

number

a new Data

returned value

received
Data
Segment
that
has been
committed
buffer or a Session Control receive buffer.

transmitted

zero,

The routine COMMIT-NUMBER returns the highest number of

Call

SPECULATE-NUMBER
message.

SPECULATE—NUMBER.(low—overhead =
<--

Page

then

Data Request message.

FLOWloc _dat
Endif

number

Segment

FLAGxmt_ack

true

Acknowledgment

transmitted.

dat)

then

different

new

acknowledgment

the

data

then

contains

> ACKxmt

Data

from

acknowledgment

Acknowledgment

causes

the

message

data
a

sent.

acknowledgment

The
sent

variable

transmitted.

Setting

process

Segment

last

number
to be

message

transmit

Data

the

must

message

to
does

send
not

in
a

need

any
Data
to

FLAGdat ack <-- true
ACKxmt dat

-~
Endif
Endif
If (message

is
(STATE =

<--

returned

value

received) then
"CC" and message

type

"Data Acknowledgment"

"Interrupt", "Data Request", "Interrupt
or "Other—Data—Acknowledgment") then

Request"

If thlS message 1s taking the port out of the "CC" state, then make an
estimate
of
the
round
trip
delay to the remote NSP (Section 7.3).
Since the port just entered the
"RUN"
state, start
the
1inactivity
timer (Section 7.4).
STATE <-- "RUN"
FLAGbuf <-- false
Call UPDATE-DELAY

stop

timer

CONFIDENCE

TIMERcon
<--

- COUNTretrans

Endif

Receiving

any message

true

<--

restarts

the

inactivity timer.

TIMERinact <-- TIME + NSPinact tim
Oncase (received message type)
When

a message

received,

execute

the

appropriate

case

statement.

Detailed Functional Model
)

Page 83

Case (Data Segment)
Process the acknowledgment field of a received
independently from the rest of the message.

(ACKNUM field present)

Data

Segment
|

message

then

Call PROCESS- DATA ACK
Endif

(ACKOTH

field present) then

Call PROCESS- OTHER DATA-ACK
Endif

(SEGNUM > ACKxmt dat) then
/
Call STORE-SEGMENT with DATA, EOM

(from MSGFLG),

and

SEGNUM
|

Else

Endif

FLAGdat ack

Case

<--

true

(Interrupt)

Process

the acknowledgment
independently from the rest

field
of
a
recelved
of the message.

Interrupt

message

If (ACKNUM field present) then
Call PROCESS-OTHER-DATA-ACK
0

Endif

If (ACKDAT field present) then
Call PROCESS-DATA-ACK
Endif

(SEGNUM =

This model of

time

NSP

ACKxmt oth

can

(Section 7.2).

only buffer

|
+

|
and FLOWloc int
=

one received

"empty")

Interrupt

1Its number must be one greater

message

then
at

than the number of

the
1last other-data
message
accepted
(contained
in
variable
ACKxmt oth).
When the variable FLOWloc int contains "empty," there is
“) room in buffer BUFrcv.
Setting
FLAGoth ack true
causes the
data
/ transmit process
to acknowledge this Interrupt message.
BUFrcv

FLOWloc
ACKxmt

FLAGoth

<--

DATA

int <-oth

<--

"interrupt"
ACKxmt _oth

ack

<--

true

FLAGothack
Endif

<--

true

Elseif

(SEGNUM <= ACKxmt oth)

then

Detailed Functional Model
Case

Page 84

(Data Request)

Process the acknowledgment field of a received
independently

from the

rest

Data

the message.

1f «(ACKNUM field present)

Request

message

then

Call PROCESS- OTHER DATA-ACK
Endif

If (ACKDAT field present)
‘Call PROCESS-DATA-ACK
Endif

then

(SEGNUM
= ACKxmt oth + 1)

then

- This model of NSP processes only one
other-data
message
at
a
time
(Section
7.2).
It
processes each one to completion.
The number of
the one it wants to process next is one greater than the one
that
1t
has
most
recently
accepted
and
processed
(and
whose number
1is
contained in ACKxmt oth).
|

Basically, the algorithm for processing a Data Request message is
check

its validity.

(1)

(3)
(4)

invalid.

Store the data "send/do
not send"

(2)

Discard

SW.

switch in variable

Increment

the

channel.

is valid,

acknowledgment

number

for

FLOWrem

the

Set the flag FLAGoth ack to true to force the

other-data

data

transmit

process to acknowledge the receipt of this message.
(Use the
~ routine SET-SWITCH-AND-FLAG.)
Update the variable FLOWrem dat, 1f necessary, by addlng
the
count from the Data Requestmessage to it.
If

(FLOWremtyp =
Call

Elseif

"none")

then

SET-SWITCH-AND-FLAG

(FLOWrem_typ = "segment")

then

The following two statements define the validity check for a
received
Data
Request
message
from a remote NSP that receives with "segment”
flow control.

”

(-128 <= FCVAL <= 127) then
If (-128 <= FLOWrem
dat + FCVAL <=
- FLOWrem _dat

Call

<--

FLOWrem dat

|
127)

then

FCVAL

SET-SWITCH-AND-FLAG

Endif
Endif

Elseif

(FLOWrem typ =

"session-control-message")

then

The following two statements define the validity check for a
received
Data
Request
message
from
a
remote
NSP
that
receives with
"session-cortrol message"

flow control.

If (0 <= FCVAL <= 127) then

Detailed Functional Model

Page 85

If (0 < FLOWrem dat + FCVAL <= 127) then
FLOWremdat <-- FLOWrem_dat + FCVAL

Call SET-SWITCH-AND- FLAG

Endif
Endif
Endif

Elseif (SEGNUM <= ACKxmt oth) then
FLAG oth ack <-|
Endif

true

Case (Interrupt Request)

Process the acknowledgment

field

a received

message independently from the rest of the message.

Interrupt

Request

If (ACKNUM field present) then
" Call PROCESS-OTHER-DATA-ACK Endif

then

(ACKDAT field present)

(SEGNUM = ACKxmt oth + 1) then

Call PROCESS-DATA- ACK
Endif

The message number check for received Interrupt Request messages 1S
the same as for received Interrupt and Data Request messages. The
received
following statement defines the validity check for " a
Interrupt

Request message.

If (FCVAL >= 0 and 0 <= FLOWrem int + FCVAL <= 127) then
FLOWrem int <-- FLOWrem 1int + FCVAL
ACKxmt oth <-- ACKxmt _ oth + 1

FLAGoth ack <-- true
Endif

Elseif (SEGNUM <= ACKxmt oth) then
FLAG oth ack
Endif

<--

true

Case (Data Acknowledgment)
Call PROCESS-DATA-ACK

(ACKOTH field present)

then

CALL PROCESS-OTHER-DATA-ACK
Endif

Case (Non-Data Acknowledgment)

Call PROCESS-OTHER-DATA-ACK

If (ACKDAT field present)

Call PROCESS-DATA-ACK
Endif

then

Endcase

Endif
Endloop

The data receive proceSses call the following routines:

Detailed Functional Model

Page 86

PROCESS-DATA-ACK:

the following

contents

segment,

Data

routine,

the

fields

Acknowledgment

(ACKrcv_dat

Message

NUMsent)

(NUMBER is processed when

'NUMhigh,

elther

then

sub-channel

1is

case,

ignore

TRYHARD

<--

CONFIDENCE

If
a

(1)

NM(ACKrcv_dat + 1,

message

in case QUAL="nak"

less

than

that

was

never

wupdates
the
flow
transmission.

equal

sent.

to
In

NUMBER)

1is

the

number of "end-

segments

(ACKrcv_dat + 1) to NUMBER, and
(NUMBER - ACKrcv_dat)
is
the

the

range

|
number

|
»
|
of data segments

range.

(FLOWrem typ = "segment")

then

FLOWrem dat

<--

FLOWrem dat

(NUMBER

FLOWremdat

<--

FLOWremdat

NM(ACKrcv _dat

(FLOWremtyp =

Endif
If ((QUAL = "nak"
<= NUMBER) then

variable

Note that there are

data

same

control

data

here:

of-message”

Elseif

Message.

constructions

the

data

true

<--

parallel

the

are

received

not

acknowledgment.

The
following
"If"
Dblock
(FLOWrem dat)
that
allows

QUAL

false
<--

COUNTretrans

(2)

the

to
ACKrcv dat,
then
this
1mp11c1tly processed before

is equal to ACKrcv _dat
nak").

acknowledging

the

and

from

then

than
or
equal
exp11c1tly
or

QUAL="cross

NUMBER

names

Data Request

NUMBER 1s not greater
acknowledgment
has
been
or

same

<= NUMBER <=

variables

the

"message")

or QUAL =
|

- ACKrcv _dat)
+

"cross sub-channel

NUMBER)

nak")

or NUMdat

NUMdat <-- NUMBER + 1

Endif
If

either this acknowledgment was a
of
the
next
Data
Segment

number

(contained in NUMdat)
acknowledged,

transmit

the

then

1less

set the

number

just

than

number

negative
acknowledgment
message that was going to

equal

the

acknowledged plus

Data

the

sent

number

Segment

just

message

only

one.

ACKrcv _dat <-- NUMBER
The following code
there 1s remaining

restarts the
data
retransmission
unacknowledged, transmitted data.

stop timer TIMERdat
If (ACKrcv dat < NUMsent) then
TIMERdat <-- TIME + (NODEdelay * NSPdelay)
Endif
If (DELAYmsg num <= ACKrcv _dat and DELAYstr tim <

timer

then

Detailed Functional Model

Page 87

is being
tim is non-zero, then a Data Segment message
If DELAYstr
Section
(see
estimate
delay
trip
round
the
to
wupdate
an
timed for
1is
number
(whose
timed
being
message
Segment
Data
the
If
7.3).
calculate
then
acknowledged,
been
just
has
num)
DELAYmsg
in
contained
the

round trip delay for

that message.

Call UPDATE-DELAY
|
Endif
Endif

PROCESS-OTHER-DATA-ACK:

the
are
the variables NUMBER and QUAL
In the following routine,
Interrupt,
received
the
from
name
same
the
of
fields
the
of
contents
Data Request, Interrupt Request, Other-Data-Acknowledgment message, Or
Data

Segment

message.

and (QUAL="nak" or QUAL="cross sub-channel
(NUMBER=NUMoth-1

nak")) then
OTHERstate <--

Endif

"timeout"”
o

then

(NUMBER = NUMoth and OTHERstate < > "ready")

outstanding other-data
single,
the
NUMoth contains the number of
OTHERstate is equal to either "sent"
any (Section 7.2).
1if
message,
1is such an
1if there
"ready")
to
equal
not
or "timeout" (i.e.,
stop the
1is acknowledged,
the message
If
outstanding message.
retransmission

timer

for

the message.

stop timer TIMERoth
TRYHARD <-- false
CONFIDENCE

<--

true

COUNTretrans <--

a timeout.
Handle a negative acknowledgment in the same manner as

If the message was positively acknowledged, then send a new other-data
message.

Setting OTHERstate to "ready" allows the data transmit process to send
another

other-data

message.

NUMoth contains the number of the next

other-data message that will be transmitted.
OTHERstate <-- "ready"
NUMoth <-- NUMoth + 1

(OTHERtyp = "interrupt")

then

OTHERtyp contains the type of other-data message that was sent and has
If it was an Interrupt message, then a new
acknowledged.
Dbeen
just
Indicate this condition by setting
one may be buffered into BUFxmt.
FLAGint avail to false.

Decrement the remote

interrupt request count.

Detailed Functional Model

FLAGint-avail <-- false
FLOWrem int <-- FLOWrem int

Elseif

(OTHERtyp =

"data

Page 88

request")

then

If a Data Request message has just been acknowledged, then
clear the
count
value
contained
in
1it,
allowing the data receive process to
obtain a new speculate number that
can
be
sent
1n
the
next
Data
Request

message.

FLOWloc_dat <-0
Endif
Endif
The

acknowledgment

any

of an Interrupt Request message
does
explicit
handling.
This 1s because a

additional

Request

message cannot

interrupt

sent

data whose request

until

was

session

just

control

acknowledged

has

not
require
new Interrupt
received

(Section

the

7.2).

SET-SWITCH-AND-FLAG:

This routine stores the data "send/do not send" value from a
received
Data
Request
message
1in
FLOWrem sw
and
sets FLAGoth ack true to
indicate that an other data acknowledgment is requ1red
|
FLOWrem sw

<--

ACKxmt

<--

ACKxmt _oth

oth

FLAGoth

Both

ack

the data

processes

call

MOD

<-- true

receive
the

processes

following

and

the

connect/disconnect

receive

routine:

UPDATE-DELAY:

This routine updates the NODEdelay
Call
the routine
temporary variable.

If (DELAYstr

with

tim <>

0)then

If (NODEdelay = 0)then

NODEdelay

Else

temp

<--

TIME

node

descriptor.

this

code,

"temp"

|
—\DELAYstr

tim

<--

TIME

DELAYStr_tim

temp <-- temp - NODEdelay
NODEdelay <-- NODEdelay +
Endif
DELAYstr tim <-- 0

Endif

variable

port argument.
In
o

|
(temp
|

/ (NSPweight
"

+ 1))

)
"

Page 89

Detailed Functional Model

all
handle
There 1s one

processes
Processes - These
map onto a reserved port.

6.4.3 Reserved Receive
received messages that

reserved port process for each reserved port.

Loop

This process

loops forever.

If (a message is received) then
If (the message 1s a Connect Initiate) then
- process

to send a No Resources message.

port

reserved

the

Setting MSGtyp to "no resources" causes

transmit

NODE <-- source node address

ADDRrem <-- SRCADDR

MSGtyp <--

"no resources”

CIRCUIT <-- CIRCUIT received from Routing
NEXTHOP <-- NEXTHOP recieved from Routing

Elseif (the.message«is'a Connect Confirm, Disconnect Initiate
- Data Segment,
Request)

)

then

Interrupt, Data Request, or Interrupt
|

Setting MSTtyp to "no-link" causes the reserved port transmit
|

to send a No-Link message.

NODE <-- source node address
ADDRrem <-- SRCADDR
ADDRtmp <-- DSTADDR

MSGtyp <--

process

"no-link"

CIRCUIT <-- circuit received from Routing
NEXTHOP <-- nexthop received from Routing

Endif
Endloop

6.5

Endif

Reassembly Module

The reassembly module has two functions. First, ‘it maps data from
Data Segment messages into Session Control buffers according to the
Because
rules implied by the Session Control interface description.
e
interfac
the
from
module
this
to
passed
is
of this, the DATA-RCV call
This
pools.
buffer
commit
and
cache
the
routines. Second, it manages
function includes flow control policy establishment. That is, this
module is aware of the amount of buffering available via Session
Control receive buffers, cache buffers, and commit buffers. It uses

’

this information to produce normal data request counts to be

Data Request
control

messages.

mechanism

transmission).

(in

sent

1in

The data transmit processes execute the flow

other

words,

the

Data

Request
-

message

Detailed Functional Model

- Page 90

The detailed description of the operation of this module
is beyond the
scope
of
this
specification. However,
it
must
operate with the
following restriction with respect to
the
management
of
the
cache
buffer
pool.
It
must
not
discard the
data from a received Data

Segment

message

for

a given

Session

Control

port

there

a higher numbered Data Segment message in the cache
Appendix C contains
an example of this module.
The

data

Segment

receive

processes

messages

that

this module.

corresponding

may

The data

changes
received

receive processes

ports.
In
requesting
data

gquaranteed

obtain

should

storage.

the

most

for

store

general

which

Therefore,

in
for
a

1is

When

the
transmit

call

represents

flow

to "SPECULATE-NUMBER"
Data-Request
message.
tradeoff

between

arriving messages

messages

and
their
Data-Request
message

piggyback
to

a data

make

the

The

cost

acknowledgments.

The

whether

acknowledgment.

intelligent

policy

port

port.

of
by

Data

calling

values

1in

the

reassembly module
necessarily
any
segments

from

any

given

that

the

time

1is

port.

a non-zero value NSP
will
decision to send this message

the

depends

data

same

returns

benefit

and

the
of

the

number

not

number

reassembly module wants to receive for a port
referred to as the "speculate number" for the

the
given

these

case,

there

the

for

precise

control

sending

cost

the

In order

for

decisions

Data-Request

the

over

sending

message

can

reassembly

parameter

the

Data-request

module
defined,

low-overhead, which is used to inform the
reassembly
module
whether
sending
a Data-Request message at this time will be inexpensive.
The
data receive processes obtain the
speculate
number
for
a
port
Dby
issuing the following call:
.
B
SPECULATE-NUMBER

port id:

(port

id, low-overhead

return:

low-overhead flag

the current number of data segments

would

data receive processes periodically
number
committed
to either a commit or

following

the acknowledgment
The

receive

call:

- COMMIT-NUMBER

data

number

processes

obtain
session

obtain

sent
this

this

module

the
highest
segment
control buffer.
This
to
the
remote
NSP
number by 1ssuing the

(port

id;

return)

port id:

a port identifier

return:

the

The data

that

receive,

The

value is
module.

return)

a port identifier

low-overhead:

;

highest

segment

receive processes attempt

Segment
messages
buffer by issuing

number:committed

put

into
a
cache,
commit,
the following call:

data

from

session

received

control

Data

receive

Page 91

Detailed Functional Model

STORE-SEGMENT (port id, data, eom, number)

identifier

a port

id:

port

data ftom a Data Segment message

data:
eom:

one of:

number :

data is’end—of—message

data 1s not end—of—message

the

segment number of

the Data Segment message

i> 6.6 Transmit Processes
This section contains algorithms for implementing'the following:
o

Connect/disconnect transmit process (Section 6.6.1)

o Data transmit processes (Section 6.6.2)

Reserved transmit processes (Section 6.6.3)

6.6.1

)

Connect/Disconnect

Transmit

Processes
- These

processes

Connect Acknowledgment, Connect Confirm,
Initiate,
transmit Connect
Disconnect Initiate, and Disconnect Complete messages.
There
1is
one
session control port connect/disconnect transmit process for each
Session Control port.
Loop

This process loops forever.
1In general if FLAGbuf 1is true a
or disconnect message requ1res transmission.
If

(STATE =

"DI"

and FLAGbuf

false

and NUMhigh = ACKrcv_dat and TIMERcon not running)

connect
|

then

This test causes this process to attempt to send a Disconnect Initiate

message

(1)
~

(2)

—

(3)

)

only

1f:

Se551on Control requested a

disconnection

there

unacknowledged

are

outstandlng,

messages (NUMhigh = ACKrcv_dat);

(i.e;,

and

Data

STATE

Segment

a previously transmitted Dlsconnect Initiate message, if any,
is not being timed out

(TIMERcon not running).

Detailed Functional

Model

FLAGbuf <-- true
DELAYstr tim <-"Endif

If
|

Page

TIMEA

(timer TIMERcon explred and STATE

then
If the

retransmission
timer
has
retransmission
count
and
attempts
message.

"CI",

explred,

send

"CC",

"DI",

NSP

|
|
increments

connect

"DR")

the
or disconnect

FLAGbuf <-- true
Call
Endif

TIMEOUT

When FLAGbuf
transmission.

been

1is

requested

true,
a
connect
or
disconnect
message requires
When FLAGcon alloc 1s true, permission to transmit has

from

the

transmit

allocation

module.

These

two

variables
act
together
to
form a state
variable
with 4 states.
Conditions that require a message to be sent can
change
dynamically.
This
process
has to
request permission to transmit but has to take
back a request it previously made if it no longer must send a message.
Therefore, interpret these variables as follows:
FLAGbuf

true,

FLAGbuf
FLAGbuf

true, FLAGcon alloc true: attempt message transmission.
false, FLAGcon alloc true: take back permission request

FLAGbuf false,
If

FLAGcon_alloc

FLAGcon
“alloc

(FLAGbuf true
Call ALLOCATE
FLAGcon

Elseif

alloc

(FLAGbuf

false°

and FLAGcon
<--

request

permission

alloc

false)

send.

then

true

false

(FLAGbuf true and FLAGcon_alloc true)

(CHECK-ALLOCATE)

do nothing.

false and FLAGcon alloc true)

Call DEALLOCATE
- FLAGcon alloc <--

Elseif

false:

then

CHECK-ALLOCATE is a Boolean function in the transmit allocation module
that

returns
The

granted.

true

state

and
only
if permission to transmit has been
port determines the message to be sent.

the

(STATE =

"CI")

DELAYstr

tim

Call
- Endif

then

<--

TIME
SEND
—~CONNECT-INITIATE with data

addressed

(STATE = "DIC," “RJ, or "DN") then
Call SEND-DISCONNECT-COMPLETE
Endif
If (STATE = "DR" or "DI") then
If (DELAYstr_tim = 0) then DELAYstr tim <-Call SEND-DISCONNECT-INITIATE
Endif

TIME

BUFcon

Detailed Functional Model
If
If

Page 93

(STATE
"CR") then Call SEND-CONNECTACKNOWLEDGMENT
"CC") then
(STATE
If (DELAYstr tim = 0) then DELAYstr tim <-- TIME

" call SEND-CONNECT-CONFIRM

Endif

If the transmission was successful, this process must
take back
1ts
request
for permission
to
transmit (to allow another process to Dbe
given an equal chance to transmit).
If

(success) then
Call DEALLOCATE
FLAGcon alloc <-FLAGbuf <-- false

false

(STATE = "CC," "DI," or "DR") then
If not (STATE = "CC" and VERSION = 3.1)
If

(NODEdelay =

then

0) then

This means that there is no current round trip delay estimate
remote

node.

The

seconds

1is

suggested

value;

the

1s not

mandatory.

TIMERcon
<-- TIME + 5 seconds

Else

An estimate does exist.

TIMERcon <-- TIME +

Endif
Endif
Endif

(STATE = "CC"

(NODEdelay * NSPdelay)

and VERSION = 3.1)

then

STATE <-- "RUN"
stop timer TIMERcon
CONFIDENCE <--true
COUNTretrans <-- 0

TIMERinact <-- TIME + NSPinact_tim

Endif
Else

If transmission is unsuccessful, calling REALLOCATE

will

give

other

ports a chance to transmit w1thout removing this port for contention
This causes
This process leaves FLAGbuf true.
for Routing resources.
the process to request permission to transmit again.
Call

Endif
Endif
Endif
Endloop

REALLOCATE

Detailed Functional Model

6.6.2

Data Transmit

Processes
- These processes

Interrupt,

Data

Other-Data

Acknowledgment

process

each

for

Request,

Session

Interrupt

Request,

messages.

Control

send

Data

There

‘Page

Data

Segment,

Acknowledgment,

one

data

port.

and

transmit

Loop

This process loops forewver.
The data receive process for

|
|
the highest
number
of
an
acknowledged Data Segment message in ACKrcv_dat.
This process informs
the segmentation module of this value by calling
ACK-SESSION-CONTROL.
It
obtains the highest segment number available from the segmentation.
routines v1a function LAST.
Call

If
If

port

puts

ACK-SESSION-CONTROL with ACKrcv dat

(STATE =
[STATE =

"RUN") then NUMhigh <-- LAST
|
"RUN" or (STATE = "DI" and
NUMhigh
<

then

With

the

exception of

the processing

above,

this process does

for
a port that is not in either the
with outstanding, unacknowledged Data

ACKrcv_dat).

If
If

the

Data

(timer TIMERdat

data

segment

message

acknowledged

timer

transmit

the

remote

<-- ACKrcv dat
TIMEOUT

the

state

most

one

nothing

the "DI"
(NUMhigh

state
<
>

then

one

the

number

greater

NSP,

than

the

highest

the other-data

(timer TIMERoth expired)

If
in

model

explres,

NUMdat

Call
Endif

"RUN" state or in
Segment messages

expired) then

retransmission

Segment

|
ACKrcv dat)]

retransmission

variable

then
timer

explres,

OTHERstate.

outstanding,

This
unacknowledged

NSP.

record

possible

other

the

since

data

expiration
there

message

can

this

te "timeout"
OTHERsta<-Call
Endif

TIMEOUT

The

tests below are completely analogous to the tests performed
in
a
connect/disconnect
transmit process.
The only difference is that the
need to transmit a connect or disconnect message could
be
determined
by
examining
a
single
flag (FLAGbuf).
But the need to send
a data
type message is
determined
by
a
complicated
Boolean
function
of
variables
in
the
port.
The
Boolean
function
MESSAGE-TO-BE-SENT
returns true 1f a message requires transmission
and is used below in a

manner

analogous

FLAGbuf

connect/disconnect

(MESSAGE-TO-BE-SENT and FLAGdat
Call ALLOCATE
FLAGdat alloc

<--

true

transmit

alloc false)

then

process.

Detailed Functional Model

Elseif

Page

(not MESSAGE-TO-BE-SENT and FLAGdat_alloc true)

Call DEALLOCATE
FLAGdat alloc <--

then

false

Elseif (MESSAGE-TO-BE-SENT and FLAGdat alloc true)
If (CHECK-ALLOCATE) then

then

If permission to transmit has been granted, then determine the type of

message

transmit

variables
in the port.

by testing

The order

collection of

Boolean

functions of

in which these functions are

tested

is
important and is part of the specification.
That is, 1f more than
one type of data message may be transmitted, the
type
that
must
be
transmitted
first
1is
important.
Also,
1f
transmission
1s
unsuccessful,
call
REALLOCATE
for
the
same reasons
as
1n
the
connect/disconnect transmit processes.

If (INTERRUPT-TO-BE-SENT) then
Call

SEND-INTERRUPT

If (success)

The

routine

‘successful
Request

then

OTHER-DATA-SENT
transmission

performs

processing

Interrupt,

messages.

Data

common

Request,

and

the

Interrupt

OTHERtyp <-- "interrupt"
Call
Else
Call
Endif

OTHER-DATA-SENT
|
REALLOCATE

Elseif (INT-REQUEST-TO-BE SENT) then
- Call SEND-INTERRUPT-REQUEST
If (success) then
|
OTHERtyp <-- "interrupt request"
Setting FLOWloc int to "empty" allows data from a
received

Interrupt

message

saved

BUFrcv

the

data

receive

process.

FLOWloc
int <-- "empty"
Call OTHER-DATA-SENT
Else
Call
Endif

Elseif

(DATA-REQUEST-TO-BE-SENT)

Call

REALLOCATE

(success)
OTHERtyp

then
<--

One reason that a Data Request
inactivity

inactivity

timer has

timer

then

SEND-DATA-REQUEST

"data

request”

message

expired (Section

restarted.

may

7.4).

be sent

1If

this

1is

the
|

that

case,
|

the the

Detailed Functional Model

Page 96

(TIMERinact expired) then
TIMERinact <-- TIME + NSPinact tim
Endif
Call OTHER-DATA-SENT
If (VERS.ON = "4.0") then
FLAGdat ack <-- false
|
Endif
Else

Call
Endif

Elseif

|
REALLOCATE

(DATA-TO-BE-SENT)

then

If there is no Data Segment currently being timed for an update to the

estimated

round

time of day.

trip delay

Also

save

(DELAYstr
tim =

the number of

(DELAYstr
tim =0)

DELAYstr_tim <-DELAYmsg num <-Endif

0),

then save the current

the Data Segment

being

timed.

then
TIME
NUMdat

Call GET-SEGMENT with segment number NUMdat
returned values

The routine DATA-ACK-SENT performs processing common to the successful
transmission of

Data Segment

and Data Acknowledgment messages.

If the Data Segment just sent
had
a
number
one greater
than
the
highest
number
acknowledged
by
the
remote
NSP,
then
start
the
retransmission timer.
The value for this timer 1s
a
constant
times
the current estimated round trip delay (Section 7.3).
|

If (NUMdat = ACKrcv dat+1l) then
~
TIMERdat <-- TIME + (NODEdelay * NSPdelay)
Endif

Increment the number of

the

(NUMdat) .

Data

(NUMdat

> NUMsent)

NUMsent

<-- NUMdat +
DATA-ACK-SENT

(VERSION =

then

false

(OTHER-DATA-ACK-TO-BE-SENT)

Call

then

"4.0")

FLAGoth ack <-Endif
Else
Call REALLOCATE
Endif
|

Elseif

NUMdat

Endif
NUMdat
Call

Segment

SEND-OTHER-DATA-ACK

(success)

then

transmitted

Call SEND-DATA-SEGMENT with
If (success) then

Detailed Functional Model

)

The

routine

OTHER-ACK-SENT

performs

processing

Call

(VERSION =

"4.0")

then

SEND-DATA-REQUEST

(success)

then

"data

request"

that
a Data
Request
message
may
timer has expired (Section 7.4).
timer is restarted
If

(TIMERinact

TIMER1nact
Endif
|

Call

Else

Call
Endif
Else
Call

)

"true")

then

OTHERtyp <--

<--

expired)
TIME

be
sent
is
that
1If this is the case,

then
NSP1nact

OTHER-DATA-SENT

REALLOCATE
|
SEND-DATA-ACK

(success)

then

Call
Else

DATA
ACK
—-SENT

Call
Endif

REALLOCATE

Endif

)

the

then

(DATA-REQUEST-TO-BE-SENT)

Call

Request,

OTHER—ACK-SENT

Call SPECULATE-NUMBER (low- overhead=
FLOWloc dat <-- returned value

One reason
inactivity
inactivity

- Page 97

Else

Call REALLOCATE
.
Endif
Elseif (DATA-ACK-TO-BE- SENT)

common

successful transmission of Interrupt, Data Request, ‘Interrupt
and Other-Data Acknowledgment messages.

)

Else

Call

SEND-DATA-ACK

(success)

Call
Else

then

DATA-ACK-SENT

Call
Endif
Endif
Endif
Endif
Endif
Endloop

REALLOCATE

‘The

are

following

routines

used by

these

processes.

tim

the
the

Detailed Functional Model

Page

TIMEOUT
:

COUNTretrans

If
If

<—— COUNTretrans

(COUNTretrans > NSPretrans)
(COUNTretrans > NSPtryhard)

then CONFIDENCE <-- false
then TRYHARD <-- true

MESSAGE-TO-BE-SENT:
If (INTERRUPT-TO-BE-SENT) then return true
Elseif (INT-REQUEST-TO-BE-SENT) then return true
Elseif (DATA-REQUEST-TO-BE-SENT) then return true
Elseif (DATA-TO-BE-SENT) then return true
Elseif (OTHER-DATA-ACK-TO-BE-SENT) then return true
Elseif (DATA-ACK-TO-BE-SENT) then return true
|
Else
return

false

Endif

INTERRUPT-TO-BE-SENT:
To

send an

(1)

interrupt message,

either:

Interrupt data must be

available

(2)

The

have

(3)

There must be no outstand1ng, unacknowledged Interrupt - Data
Request, or Interrupt Request message (OTHERstate = "ready").

true),

remote

NSP

must

(FLOWrem int > 0), and

(1)
(2)

BUFxmt

requested

the

(FLAGint avail
1interrupt

data

There
must
be
an
outstanding,
unacknowledged
Interrupt
" message (OTHERtyp = "interrupt"), and
The message must have timed out (OTHERstate = "timeout").

(FLAGint avail

true and FLOWrem
int >

and OTHERstate = "ready") then

return

Elseif

true

(OTHERstate = "timeout"
and OTHERtyp = "interrupt")

return
Else
return
Endif

)

then

true
|
false

INT-REQUEST-TO-BE-SENT:

To send an Interrupt Request message,
(1)

(2)
or

The buffer BUFrcv must be

message

not

and

either:

empty and an

previously sent

(FLOWloc int

Interrupt

"send

Request

request”);

There must be no outstanding, unacknowledged Interrupt,
Request,

Interrupt Request message

(OTHERstate =

Data -

"ready"),

)

Detailed Functional Model

)
’

(1)

There must

(2)

The message must have timed

Request message

(FLOWloc_int
return

Elseif

an outstanding,

(OTHERtyp =

"send request"

true

(OTHERstate

request,”

Page

unacknowledged

"interrupt

out

and OTHERstate =

Interrupt

request");

(OTHERstate =

and

"timeout").

"ready")

then

"timeout"

and

OTHERtyp =

"interrupt

then

return true
Else
return
Endif

false

DATA-REQUEST-TO-BE-SENT:

To send a Data Request message,

either:

(1)

There must be an unsent request count (FLOWloc
dat

0);

(2)

There must be no outstanding, unacknowledged Interrupt,

Data

and

Request,

Interrupt

Request message

(OTHERstate

)

= "ready").

(1)
\>

‘The activity timer must have expired (TIMERact expired);

(2)

There must be no outstanding,

Request,

or Interrupt Request message

(1)

unacknowledged
|

Interrupt,

(OTHERstate =

The message must have timed out

(FLOWloc dat

return

Elseif

(TIMERinact

return

Elself

true

(OTHERstate =

0 and OTHERstate= "ready")
expired and OTHERstate

Data

Request

"timeout").

then

"ready")

then

true

(OTHERstate = "timeout"
and OTHERtyp = "data request”)

return

"ready").

There must be an
outstanding,
unacknowledged
message (OTHERtyp = "data request");
and

(2)

and

Data

then

true

Else
"return

false

Endif

OTHER-DATA-ACK-TO-BE-SENT:

return FLAGCth_ack
DATA-TO-BE-SENT:
If

(NUMdat

<= NUMhigh and FLOWrem
sw =

"send")

then

To consider sending the next Data Segment to be transmitted
(the
one
with
number
NUMdat), the Data Segment must be available from Session
Control (NUMdat <= NUMhigh) and the remote NSP must be
allowing
data
to
be
sent
(FLOWrem
sw
= "send").
Note that the next Data Segment

Detailed Functional Model

message to be sent is always one

that

Page'lOO

wunacknowledged

since

the

that

was

variable NUMdat is always greater than ACKrcv_dat, although there will
be no data to send if NUMdat = ACKrcv dat + 1 = NUMhigh + 1.
The

remaining tests depend on

the

type

selected by the remote NSP when the logical
If

(FLOWrem typ =
return

flow

control

link was established.

"none") then

true

The two tests below are analogous.
Each is
testing
to
see
1f
the
number of requested elements (segments or Session Control messages) is
greater than or equal to the number of elements in the range from
the
‘highest
acknowledged
(ACKrcv _dat)
to
the one whose transmission is
being attempted (NUMdat).
|
Elseif

(FLOWrem typ

return

Elseif

"segment"

and NUMdat <= ACKrcv _dat + FLOWrem dat)

then

true

(FLOWrem typ = "session-control-message"

and NMTACKrcv dat + 1,NUMdat)

return

true

Else
return

<= FLOWrem dat)

then
|

false

Endif
Else

return

false

Endif
DATA-ACK-TO-BE-SENT:

return FLAGdat_ ack
OTHER-DATA-SENT:

Call OTHER-ACK-SENT
OTHERstate <-- "sent"

TIMERoth <-- TIME +

(NODEdelay * NSPdelay)

OTHER-ACK-SENT:
Call MESSAGE-SENT
FLAGoth ack

<--

false

DATA-ACK-SENT:

Call MESSAGE-SENT
FLAGdat ack <-- false.
MESSAGE SENT°

This routine ascertains 1if there is more data to be sent.
If
so,
1t
calls REALLOCATE to remain in contention for transmit resources but to
free those resources for other ports. If not, it calls DEALLOCATE
to
free
the
resources and remove itself from contention.
1In the latter

‘j ~

Page 101

case, it sets FLAGdat alloc false so that an ALLOCATE request will

made when there

is data to send.

(MESSAGE-TO-BE-SENT)

Call
Else

Dbe

then

REALLOCATE
|

Call DEALLOCATE

FLAGdat alloc
Endif

Detailed Functional Model

<--

false

6.6.3
Reserved Transmit Processes - The reserved
transmit
processes
send No
Resources
and No-Link messages.
There
1s one reserved
transmit process

for each reserved port.

Loop

)

‘>

The processing here is somewhat complicated due
to
the interaction
with
the
transmit
allocation module
and the fact that a transmit
request to Routing may fail.
It is not
modeled
analogously
to
the
connect/disconnect
and
data
transmit
processes because the need to
transmit a
given message
will
not
disappear
as
with
the
other

processes.
If

(MSGtyp < >

"none")

then

Call ALLOCATE
-~

Loop

Call

CHECK-ALLOCATE

(success)

then

(MSGtyp = "no resources”") then
Call SEND-NO-RESOURCES
Elseif (MSGtyp = "no-1link") then
If

Call
Endif

SEND-NO-LINK
|

(success)

MSGtyp <-- "none"
Call DEALLOCATE
Exitloop
Else

Call
Endif
Endif
Endloop
|
Endif

Endloop

|
REALLOCATE

Detailed Functional Model

6.7

Transmit

Page

102

Format Module

This module manages the large and small transmlt buffer pools, formats
outgoing
NSP
messages,
and sends messages to Routing.
In addition,
although 1t is not explicitly modeled, this module
polls Routing
to
get
Dback
buffers
that have been transmitted.
When such a buffer is

returned,

The

immediately placed

back

its

pool.

name

call

of each routine in this module describes
supplies the appropriate port id.

SEND-CONNECT-INITIATE (port

large

transmit

allocate

large

buffer is
=

'MSGFLG

Each

avallable)

"retransmit

then

buffer

the MSGFLG <--

Else

Endif

function.

id):

transmit

(COUNTretrans

its

"connect

|
initiate"

connect

initiate"

SRCADDR <-- ADDRloc
SERVICES

<--

INFO

"version

<--

SEGSIZE

<--

DATA-CTL

Call

"segment"

4.0"

NSPbuf

<--

data

addressed

ROUTING-TRANSMIT with

BUFcon

"return

CIRCUIT,

nexthop

sender"

return

then

success

Else

release

large

transmlt

return

failure

Endif

buffer

Else

return
Endif

failure

SEND-CONNECT-ACKNOWLEDGMENT

Lgprt

(a small

transmit buffer

allocate

small

MSGFLG <-DSTADDR

Call
Else

<--

transmit

id)
s

available)

buffer

"connect acknowledgment"
ADDRrem

SEND-SMALL-MESSAGE

return
Endif

fallure

circuit
-

NEXTHOP

(success)

and

then

Page 103

Detailed Functional Model

)

SEND-NO-RESOURCES (port. id):
If (a small transmit buffer is available)
allocate small transmit buffer
MSGFLG <-- "disconnect confirm"
DSTADDR <--

then

ADDRrem

SRCADDR <-- 0
REASON <-- 1
Call SEND-SMALL-MESSAGE
~
Else
|
return failure
Endif

SEND-CONNECT-CONFIRM (port id):

If (a small transmit buffer is available) then

allocate small transmit buffer
MSGFLG <-- "ccnnect confirm”
DSTADDR <--

ADDRrem

SRCADDR <-- ADDRloc
SERVICES <-- "segment"
INFO <-- "version 4.0"
SEGSIZE <-- NSPbuf
DATA-CTL

)

<--

BUFxmt

Call SEND-SMALL-MESSAGE
Else

return failure

Endif

SEND-DISCONNECT-INITIATE

(port id):

If (a small transmit buffer is available) then
\

allocate small transmit buffer
MSGFLG <-- "disconnect initiate"

|
DSTADDR <-- ADDRrem
SRCADDR <-- ADDRIloc
REASON <-- first two bytes of BUFxmt
DATA-CTL <-- remaining bytes of BUFxmt

‘>

Call

SEND-SMALL-MESSAGE

Else

return
Endif

failure

SEND-DISCONNECT-COMPLETE (port id):
If

(a small transmit buffer is available)

allocate small transmit buffer
MSGFLG <-- "disconnect confirm"
DSTADDR

)

<--

ADDRrem

SRCADDR <-- ADDRIloc
REASON <-42

Call SEND-SMALL-MESSAGE
Else

return
Endif

failure

then

Detailed Functional Model

SEND-NO-LINK
If

(port

(a small

Page

id):

transmit buffer is

available)

then

allocate small transmit buffer
MSGFLG <-- "disconnect conflrm"

DSTADDR <-- ADDRrem
SRCADDR
REASON

Call
Else

<-<--

SEND-SMALLMESSAGE
|

return
Endlf

fallure

SEND—DATA—ACK
If

ADDRtmp

(port

id):

(a small

transmit buffer

allocate

small

MSGFLG

<--

DSTADDR

<--

SRCADDR <-NUMBER

QUAL

<--

transmit

"data

available)

then

buffer

acknowledgment"

ADDRrem

ADDRloc
ACKxmt dat

"ack"

Call SEND SMALL-MESSAGE
Else
return failure
Endif
SEND-OTHER-DATA-ACK

(port

(a small

transmit

allocate

small

MSGFLG
DSTADDR

SRCADDR
NUMBER

<-<--

id):

buffer

transmit

"other

data

ADDRrem

ADDRloc
ACKzxmt

Oth

QUAL <-- "ack"
Call SEND-SMALLMESSAGE
Else
|

return
Endif

fallure

is available)
buffer

acknowledgment"”

then

104

Page

Detailed Functional Model

SEND-DATA-SEGMENT (port id, buffer descriptor, eom,
If (a large transmit buffer is available) then
allocate large transmlt buffer
eom, bom
- MSGFLG <-- "data,"
ADDRrem

DSTADDR <--

SRCADDR <-- ADDRloc

NUMBER <-- ACKxmt dat
QUAL

<--

NUMBER

"ack"

<--

QUAL <--

ACKxmt oth

"cross

sub-channel

ack”

SEGNUM <-- NUMdat

DATA <-- data from buffer descr1ptor
Call ROUTING-TRANSMIT with circuit = CIRCUIT,
‘>

nexthop = NEXTHOP and tryhard = TRYHARD

If (success)
return

then

success

Else

release large transmit buffer

return
Endif
Else

return
Endif

failure

SEND-INTERRUPT (port id):

If (a small transmit buffer is available) then
allocate small transmit buffer
MSGFLG <-- "interrupt"
DSTADDR <--

ADDRrem

SRCADDR <-- ADDRIloc
NUMBER <-- ACKxmt oth
QUAL <-- "ack"

)

SEGNUM <-- NUMoth
DATA <-- BUFxmt

-MESSAGE
Call SEND- SMALL
Else

return failure

Endif

bom)
:

105

Detailed Functional Model

Page 106

SEND-DATA-REQUEST (port id) s
If

(a small

transmit

allocate

small

buffer

is available)

transmit

buffer
MSGFLG <-- "data request"
DSTADDR <-- ADDRrem
SRCADDR
NUMBER

<-<--

ADDRloc
ACKxmt

oth

QUAL <--

"ack"

NUMBER

ACKxmt dat
"cross sub-channel

QUAL

<--

SEGNUM <-FC MOD <-FCVAL

then
|

INT

ack"

NUMoth
"send"

<--

"data"

FCVAL <--

FLOWloc dat
Call SEND-SMALL-MESSAGE

-~
Else

failure

return
Endif

]

SEND-INTERRUPT-REQUEST (port

(a small transmit buffer is available)
allocate small transmit buffer
MSGFLG <-- "interrupt request"
DSTADDR <-- ADDRrem
SRCADDR <--

ADDRloc

NUMBER <--

ACKxmt oth

QUAL

<--

SEGNUM

NUMoth

"send"

FCVAL

INT

<--

FCVAL

<--

Call
Else

then

"ack"

<--

FC MOD <--

"interrupt"
'

SEND-SMALL-MESSAGE

return
Endif
The

id):

following

failure

routine

used by

the

above

routines.

SEND-SMALL-MESSAGE:

Call ROUTING-TRANSMIT with circuit = CIRCUIT, nexthop
and

tryhard

(success)
return

then

success

Else
release

return
"Endif

TRYHARD

small

failure

'
transmit

buffer

NEXTHOP

Detailed Functional Model

Page 107

) 6.8.»Segmentatiofi Module
transmit
from Session Control
The segmentation module maps data
by
implied
rules
the
to
according
messages
Segment
Data
into
buffers
the
makes
module
The
specification.
interface
Control
the Session
data available to the data transmit processes. Because of this, the
interface routines pass the DATA-XMT and XMT-POLL calls to the module.

The detailed specification of this module is beyond the scope of
specification

(Appendix B).

this

A data transmit process obtains a buffer descriptor for a segment of a
session

control

this

from

message

module by issuing the following

call:

GET-SEGMENT (port id,

number;

return)

number :

the number of the desired segment

returns:

a buffer descriptor for the segment, an
end-of-message
and a beginning-of-message indication
indication,

longer
no
will
it
A data transmit process informs this module that
require a segment or sequence of segments by issuing the following
|
.
call.

_> ACK-SESSION-CONTROL (port id,vnumber)
|

a segment number;
number will be

number

process.

lower
a
no segment with this or
required again by the data transmit

A data transmit process obtains the number
in
as "end-of-message"
segments marked
numbers by executing the

data
Session Control
of
range of segment
a given

following function:

1> NM (port id, i, j; return)
i

~ a segment number

a segment number

returns:

the returned number of end-of-message segments
1in
the
range of segments from number i to number j, inclusive

i<=7

0 in all other cases
A data transmit process obtains information
on the amount of
transmit
from the session control by executing the following
data available

)

function:

Detailed Functional Model

LAST (port id;

the highest segment number that could

data

Transmit

avallable

resources

across

are

for

transmission

all

must call this module to
This module guarantees
logical

links.

system-dependent

this specification
identifier.

(Appendix

and

D).

The

are,

The

(port

algorithms

following call:

obtain
the fair

therefore,

argument

A transmit process reqdests permission
ALLOCATE

executed

"port

transmit

(port

returns:

true

false

than

one

a message

After

obtaining

this

call

another

port

1issuing

the

transmit

Dby

sent

not

cannot give
at a time,

that

sent

permission

longer

needs

id)
perm1551on

the next

transmit

call

(port id)

transmit,

transmit

belfore permission

process.

transmlt process indicates
attempt
a transmit, but that
‘the following call:

REALLOCATE

may

1f
a message may

allocation module
transmit process

(port

1is

id)

A transmit process indicates
issuing the following call:

DEALLOCATE

this

scope

1id)

CHECK-ALLOCATE

transmit

id"

the

transmlt process checks to see 1f it has permission
executlng the following Boolean function:

Control

permission
to
use of Routing

beyond

- The

assigned

from Session

Allocation Module

Each transmit process
transmit
a
message.
module

108

return)

return:

6.9

Page

that

process must

transmit

it
has
wused
its
also has more data to

can be

1issue

given

permlss1on
to
send by issuing

Algorithms 7.0

Page 109

ALGORITHMS

This section contains an overview of
some
algorithms collectively
These algorithms are explicitly
executed by several NSP components.
1in
explanation
The
"defined in Section 6 in the model description.
this section is added as an aid to understanding.

7.1

Data Segment Retransmission

several
The data retransmission algorithm described in Section 6.6 in
each
for
timer
one
only
is
There
follows.
the modules operates as
of

start
(or retransmitted),
" port. When a Data Segment is transmitted
is,
That
segment.
"oldest"
the
is
sent
the timer if the segment being

highest segment
the
than
greater
1is one
number
the segment
the timer upon
restart
Also,
receiver.
from the remote
acknowledged
receipt of a data acknowledgment that acknowledges data segments
that
have not
previously
been acknowledged but that does not acknowledge
Stop the timer wupon receipt of
all outstanding data segments.
acknowledgment of all outstanding segments.

that
expired,
When a data transmit process detects that a timer has
be
can
that
Segment
Data
next
the
of
number
the
process sets
that
segment
highest
the
of
value
the
than
greater
transmitted to one
has
been
acknowledged
from the
remote
receiver.
This
causes
It
retransmission if the flow control variables allow retransmission.
there
because
however,
retransmission,
a
cause
necessarily
not
will
may have been a change to the flow control variables.

An implementation of NSP may elect to provide an algorithm different
each
An algorithm that times
one described above.
the
from
of
level
higher
a
provide
would
separately
Segment
Data
outstanding
of
cost
a
at
users)
end
by
seen
delay
average
of
terms
(in
service
more data base

7.2

storage

for NSP.

Other-Data Handling

than
No more
Handle other-data subchannel transmission as follows.
The
port.
given
a
for
time
a
at
outstanding
is
message
other-data
one
an
variable OTHERstate contains the state of the port with respect to
other-data message.
It may have the following states:
-

State

"ready”

"sent”
"timeout"

Meaning

other-data

has

message

acknowledged.

been

sent

but

not

'An cther-data message

has

been

sent,

has

not

been

An other-data message

has

been

sent,

has

not

been

acknowledged,
acknowledged,

and is being timed.
and has timed out.

Algorithms

When the port

in a state other

Page

than

"ready,"

contains
the
other-data
message type that
the variable NUMoth contains its number.

Other-data

subchannel

either

Data Request message or

update

the

(FLOWrem_dat
Interrupt

Since

message

this

message
There 1s

and

receiving

corresponding
the

a time, handle
interrupt flow

count

placement

flow

receipt

variable

The

receipt

data

can buffer only one

port

BUFrcv.

received

Interrupt
follows.

attached
state of the
are:

current

The

causes

the

control for Interrupt data as
control state machine conceptually

The

and

states

Meaning

"empty"

The

Request message

interrupt

to BUFrcv.
This machine has three states.
machine is contained in variable FLOWloc int.

State

OTHERtyp

transmitted,

follows.

an Interrupt

respectively).

implementation model

at
an

handled

request

FLOWrem int,

causes

the variable

has been

110

BUFrcv

been

state

is empty, and an Interrupt Request
message
sent or the logical link has just entered the

(in which there is

Interrupt

"interrupt"”

message).

implied

session

call

"send request"

control

BUFrcv

get

should

the

has

not

yet

sent

one

Interrupt message,

and

issued

data.

empty,

for

BUFrcv contains the data from an

request

INTERRUPT-RCV

and
to

Interrupt

request

has
RUN

Request

additional

message
Interrupt

message.

Because

this model

message

cannot

request”

and

Dbe

for

sent

OTHERstate

interrupt
for

the

flow

first

control,

time

unless

Interrupt

FLOWloc int

"ready."

Request
=

"send

‘An

implementation of NSP may
other-data
error
and
flow
implementation
could
time

elect to use a
different
algorithm
for
control
from
the
ones
described.
An
each
outstanding
Other-Data
message
separately.
This would provide a higher level of service (in terms of
average delay seen by end users) at a cost of more data
base
storage
for
NSP.
An
1mplementation
could
buffer
more than one Interrupt

message

concurrently.

interrupt

flow

Interrupt

Request

for

receipt

The

control
message

1is

only

restriction

that,

unlike

cannot

the interrupt

data

sent

1in

normal
unless

the

data

operation

flow control,

space

requested.

1is

guaranteed

”

7.3' Retransmission Timer Value Estimation
NSP

must

compute

the

appropriate

value

for

the

time

within

which

retransmit certain messages.
If the value
is too great, end users may
detect unusually long delays, since Routing may drop packets.
If
the
value
1s
too small, NSP may make very inefficient use of the Routing
bandwidth.

Page 111

Algorithms

NSP attempts to maintain an estimate of the current round trip delay
Variable
" to each remote node with which it 1is communicating.
1is
estimate
The
value.
this
contains
NODEdelay in a node descriptor
An
made.
is
delay
trip
round
of
updated each time an observation
in response to
observation can be made whenever NSP receives a message
a Connect
sends
NSP
Whenever
message.
a previously transmitted
1t saves
message,
Initiate
Disconnect
or
Initiate, Connect Confirm,
NSP
Whenever
im.
DELAYstr_t
variable
in
the current time of day
Disconnect
Confirm,
Connect
nt,
receives a Connect Acknowledgme
Complete message, Oor any message acknowledging a Connect Confirm, NSP
observes the round trip delay to be the current time minus the value
|

DELAYstr tim.

In addition, sample round trip delays are observed by timing selected,
To conserve space, use only a
transmitted Data Segment messages.
may choose to operate with
ion
implementat
An
single timer per port.
tend to produce better
would
operation
Such
timers.
multiple
estimates at a cost of more data base storage.

Observe the Data Segment timing by starting the timer (provided it
when

not

already

running)

implicit)

acknowledgment

Data

Segment

message

needs

1is

transmitted the first time and by stopping the timer when an (explicit
is

for

received

Do not

the message.

since the
restart the timer if the Data Segment 1is retransmitted,
first need
from
delay
average
the
estimate
to
attempting
algorithm 1is
trip
round
observed
an
Once
ent.
acknowledgm
eventual
to
to transmit
sample is taken as described above, average the value with the current
te of a weighting factor. The formula for this 1is:
by means
estima

NODEdelay =

NSPweight * NODEdelay + deltaT
—-—-—-—————=——=——=————————————————=
NSPweight + 1

= NODEdelay +

whére:<NSPweight

NODEdelay
deltaT

deltaT - NODEdelay
—-——————=———=————=-NSPweight + 1

the weighting factor

the estimated round trip time
the sample round trip time

Note that if NSPweight is equal to a power of 2
computation can be performed easily.

minus

then

this

a message is a
The time that NSP uses to determine when to retransmit
constant times the estimated round trip delay time. This constant 1is
the "delay factor" and is contained in variable NSPdelay in

The

delay

factor

and

the

weighting

factor

are

NSP

Table

parameters.

NSPweight is an integer in the range0 to 255, inclusive. NSPdelay is
0 to 15 and 15/16,
in the range
a value 1in sixteenths of a unit
inclusive.

Algorithms
7.4
- If

- Page 112

Inactivity Timing
two

time

NSPs

cannot

communicate

(for example,

problem

or
'1s

_~‘

results.

because
An

end

with

each

the network

user

that

other

for

sufficiently

is disconnected),
either

not

using

the

long

following

logical

1link

1s paSsively waiting to receive would not necessarily know that it
uselessly consuming resources by
maintaining
the
1logical
1link.

Therefore,

NSP

contains

there

from

the

no received

The

1inactivity

remote

NSP

algorithm

traffic
for

each

timing

exercise

(either

data

logical

link.

algorithm

the

NSP

logical

control
-

operates

link

when

messages)
|

follows.

Start

"inactivity"
timer
when a
1logical
1link
enters the RUNNING state.
Restart the timer whenever a message is received for the logical link.
If the timer expires, NSP attempts to send a Data Request message that

does

not

change

the

remote

NSP's

communications
retransmission

are
not
possible
algorithm causes NSP

Data

message.

Request

CONFIDENCE variable

flow

Retransmission

described

control

variables.

to
the
remote
to
periodically
can

result

below.

NSP,
then
retransmit

the
the

the

change

7.5' Confidence Testing
A given NSP module cannot know whether or not a
network
path exists
between 1t and a given second NSP module, even if the two modules have
communicated in the past.
Therefore,
NSP
cannot
give
a
"network
disconnection"
signal
to
Session
Control when the physical network
supporting a logical link fails.
To provide some useful
counter
1n
variable

timeout

occurs

- Segment,

Link

variable

and

(NSPretrans).

CONFIDENCE

(for

Connect

Service,

compares

false.

previously

information to Session Control, NSP maintains a
COUNTretrans
in
a
port.
Each time a message
or

COUNTretrans

Whenever

unacknowledged
zero.

NSP

CONFIDENCE call.

returns

greater,

receives
the

Disconnect

message)

global

message,

COUNTretrans

NSP

Control

Confirm,

Interrupt

NSP

Data

increments

this

"retransmit

threshold”

then NSP sets variable

acknowledgment

sets CONFIDENCE to

CONFIDENCE

When communicating with a Version 3.1 neighbor,’an

~this
of a

Initiate,

variable

true and
Session

implementation

specification may set CONFIDENCE false immediately upon detection
failure of the physical link to the neighbor.

‘Message

)

8.0

Page

Formats

113

MESSAGE FORMATS

This section specifies the formats for NSP messages.

8.1

Message Format Notation

The following notation is used

herein:

FIELD

(LENGTH)

describe

the

contained

description
of field

CODING

FIELD

the name of

LENGTH

the length of the field as:

messages

where:

the

field being described

A number meaning number of

8-bit bytes

(octets)

a "B" meaning number of bits
A number followed by

The letters "EX-n" means extensible field.

specifies the maximum length of 8-bit

number

that

fields
bytes.

The high-order
bit of

interpretation,
as
protocol before
bytes in the
no
number
is
specified,
the
described below.
If
1
byte.
Extensible
is
current
maximum
length

are

variable

length consisting of 8-bit
each

byte

1indicates

whether the next byte is part of the same field.
A
A
O
1 means the next byte is part of this field.
is the last byte. The
indicates
the
next
byte
low-order 7-bits
of each byte are information bits.
Extensible
fields
can
be
binary or bit map.
If
they are binary, then 7-bits
from
each
byte
are
concatenated
1into
a single binary field.
If they
are bit map, then 7-bits from each
byte
are
wused
independently or in groups as information bits.

NOTE
=]

The

bit

definitions

define

information
bits
after
removing
extension
bits and
compressing
bytes.
o

the

the
the

The letters "I-n" means this is an image field.
1S

a number specifying the maximum length
of 8-bit

" bytes

in the

image.

A 1-byte

count of ‘the

1length |

remainder of the field precedes the image.:
Image fields are variable in length and may be null
each
byte
are
All
8-bits. of
0),.
=
(count

the

Message Formats

information bits.

each

1image

Page

The meaning

field

and

114

interpretation

is defined with that specific

field.

CODING

Is the representation type used as follows:
A
B

7-bit ASCII
Binary

Bit map
(each
bit or
independent meaning)

group

Constant

null

Interpretation data dependent

bits

has

NOTES
1.

If both the length
and
coding
are
omitted,
the
field represents
a generic field with
a number of
subfields specified in the description.

Any bit or field specified as

3.
4,

zero unless otherwise

noted.

All numeric values

Bits

with

unless otherwise noted.

are

numbered

this
bit

"reserved"
section
0

(low-order, least-significant bit)

‘left
(high-order,
convenience,
when

must

are
the

decimal
right

and bit 7 on the

For
2-byte
field is given, it will be
shown
converted to
a
16-bit
word.
When
a subfield of a message field
contains more than one bit, it should be considered
a binary value.

Unless otherwise
at
the
top
of

positions.

most-significant
bit).
the
graphic
form
of a

specified, the numbers that appear
the message formats represent bit

Bracketed fields are optional.

Message

8.2

Page 115

Formats

General Message

Format

In general, NSP messages have the following format:
m——————— tmm——————— +

MSGFLG

MSGDATA

o ————— o ————— +

MSGFLG

(EX)

Is a group of fields describing the characteristics of the message. The MSGFLG format 1is:

t———t———t
-t
==t ——— ——— ¢

Bit:

4[|

311211110

+—-——+—-——F———t———t———t—
——— ——t
——+

Set

to:

SUBTYPE

(3B)

Type

|
|
|
|
|
|
|
|
|

|
|
|
|
|

|
‘|
|
|
|
|
|
|
|

TYPE

the message

modlfy

TYPE

subtype

|
|

Meanlng

|
|
|
|
|
|
|
|
|

0
1
1

(Bits).

5
6

5
5
6

used

ittt

Bit set to/

0
1
0

Data Segment
Interrupt or Link Service
Beginning-of-Message
segment (bit 4 = 0)
End-of-Message
segment (bit 4 = 0)
Link Service (bit 4 = 1)
Interrupt (bit 4 = 1)
reserved (bit 4 = 1)

0
1
2
3
0

Data Acknowledgment
Other-Data Acknowledgment
Connect Acknowledgment
reserved
reserved

——— T
T pu—— o

|
|
]
|

4-5

|
|
|
|
|

field.

Subtype

|
|
|
|
|
|
|
|
|
+

|
|
|
|
|

fm————— Fm——————— e +

{

|
|
|

|
|
|
|
|
|
|

|
|
|
l
|
|
|

4-6

control

|
|
|

|
|
|
|
|
|
|

3
4
5

6
7

type

(binary):

}

No Operation (included for
compatibility with NSP 3.1)
Connect Initiate

|
|
|

Connect Confirm

Disconnect Initiate
Disconnect Confirm
reserved (Phase II node
init)
Retransmitted Connect
~ Initiate
reserved

|
l
|
I
|
I
I

—— Fmm——————— o - +

TYPE (2B) : B

1
2
3

8.3

Page 116

Is the message type (binary)
0

data message

acknowledgment message
control message
|
reserved

Is the remainder of an

MSGDATA

Message Formats

3-5).

NSP

Data Messages

There are three types»of'déta messages:'
l;. Data Segment messages (Sectidn 8.3.1)
2.

Interrupt messages (Section 8.3.2)

Link Service messages (Section 8.3.3)

message

(Section

8.3.1
form:

Message Formats

Page 117

g
Data Segment Message - A Data Segment message has the followin
|
|

—— t————————— e ———————— mm—————— +————+

fm—————— o

| [ACKOTH] | SEGNUM |DATA|

| MSGFLG | DSTADDR | SRCADDR | [ACKNUM]

——— t———————— +-————+

m——————— m————————— t————————— - ———— ———t e

MSGFLG (EX) : BM

this

field

Bit:
|

Set to:

The format

Represents the message identifier.
1is:

4t~ —t———t———F———F———F———+t—-——+

7161 514113121110

———t———t———t———F———F———F———+

| 0 |EoMIBOM| 0 | 0 | O | 0 | O |

t———t——m—F———t———t———t———t———t———+

where:

: BM Is the end-of-message indicator
EOM (1B)
not-end-of-message
end-of-message

0
1

BOM (1B) : BM Is the beginning-of-message
0

DSTADDR (2) : B
SRCADDR (2)

: B

ACKNUM (2) : BM
|
|

indicator

not—beginning—of—méssage

beginning-of-message

Is the logical link destination address.
Is the logical link source address.

Is the number of the last NSP Data Segment message
positive
a
and
recelved
successfully
acknowledgment (ACK) or a negative

(NAK) .

field is optional.

This

set.

by bit 15 being
indicated

this field is as follows:

Bit:

Set to:

acknowledgment

1Its presence is

The

for

format

——— +
e ———— e

o |

12 | 11

| 15 | 14

—— -+
e ——— e

| 1

QUAL

fm————F e

NUMBER

——— +
————— e

where:

QUAL (3B) : B

Is anlacknowledgment qualifier.
0
1

ACK
NAK

2-7 reserved

Message

Formats

Page

NUMBER

ACKOTH

(2)

(12B)

118

Is the number of the message
being acknowledged.

Is the number of the last NSP Other
Data
message
successfully
recelived
and
a
positive
acknowledgment (ACK) or a negative acknowledgment

(NAK).

This

field is optional.

indicated by bit
this field is as

15 being set.
follows:

e e

Bit:

bt TP b

1Its presence

The

format

for

me+

ee
-+

Set

to:

S e

QUAL

NUMBER

where:

"QUAL (3B)

Is an acknowledgment qualifier.
0,1
3

reserved
Ccross sub-channel
Cross sub-channel

4-7

reserved

NUMBER (12B)

SEGNUM

(2)

Is the
format

the

being

number of this
for this field

number

ACK

NAK

the message

acknowledged.

Data
is:

Segment

message.

The

et
T
Uy +

Bit:

e ———————— e +

Set

to:

NUMBER

e ———————— t————————— +

DATA

the

data

to be

sent

over

logical

link.

This

field is
transparent
and
may use all 8-bits of
each byte.
The
length
of
the
data
field
is
ascertained
from
the
total
1length
of the Data

Segment

message

after

and

the

consists

SEGNUM

field.

all

bytes

the

MessagelFormats

Page

following

the

has

message

- The Interrupt
8.3.2 Interrupt Message

119

form:

——————— f———————— tmmmm————— o ————— fm—————————— PR — +————- +

- ————— e —————— t————————— +————————— t—————————— t————————

MSGFLG (EX) : BM

Bit:

Set to:
|

is:

7161

5141

this

Link

et e

Mtk tte bl

e T

format

The

Is the message identifier.

field

3121110l

4———tp———pm———t———t———p———t———t+———+

111101101l

01l O]

$m——t———t———t———f———t———F———t———+

DSTADDR (2)

: B

Is the logical link destination address.

SRCADDR (2)

: B

Is the logical link source address.

ACKNUM (2)

: BM

Interrupt

Is the number of the last NSP

received and a
successfully
message
Service
negative
a
or
(ACK)
positive acknowledgment
1is optional.
field
This
(NAK).
acknowledgment
set.
being
15
Its presence is indicated by bit
The format for this field is as follows:

————— - +

Bit:

Set to:

-L
——t———r———————— e ————

NUMBER

‘QUAL

—+
o Fmm -

where:

Is an acknowledgment qualifier.

QUAL.(3B) : B

~ NUMBER (12B)

ACKDAT (2) : BM

ACK

NAK

2-7

reserved

Is the

: B

being

number

message

the

acknowledged.

Is the number of the last NSP Data Segment message

successfully

acknowledgment

This

(NAK) .

field is optional.

indicated by bit 15 being

this
|

Bit:

Set to:

acknowledgment

15| 14

format

———— +

+————tm———_—————— -

1Its presence 1is

The

follows:

is as

field

set.

positive

and

received

(ACK) or a negative

+————p————————— - ————— —_———————+

QUAL

NUMBER

___ 4

+————t———_—————— + _______________

for

Message Formats

Page 120

where:

(3B)

Is
=W
N O

QUAL

NUMBER (12B): B
|

SEGNUM (2) : BM

for

, 1

reserved

-7

cross

sub-channel
ACK

Cross

sub-channel

being

this

NAK

reserved

Is the

Is the number
format

an acknowledgment qualifier,

number

this Interrupt

field

the

message

acknowledged.

is:

message.

The

+———-% ————— e +

Bit:

12 |

————_————— o +

Set

to:

NUMBER

————————— e
- +

DATA

Is the

interrupt data.

This field

transparent

and
may
use all 8-bits of each byte.
The length
of the data field is ascertained
from
the
total
length
of
the
Interrupt message and consists of
all bytes
1in the message after the
SEGNUM
field.
Interrupt

data

may

be no

longer

than

bytes.

MesSageaFormats
8.3.3

Message - The

Service

Link

following

Page

form:

Link

Service

message

has

121

the

t—————— pmm—m——
e m——————
— fm———————— o —————— t—————— tm—————— t—————+

|SEGNUM |LSFLAGS |FCVAL]|

IMSGFLG |DSTADDR |SRCADDR |[ACKNUM] |[ACKDAT]

——————— t——————— o ———— - —————— +————————— b ———— +————- +

MSGFLG (EX) : BM
|

Is the message’identifier.
|

format

this
|

+%——+———+———+———+-——+———+———+———+

Bit:

514131

0Ol

21}110

-t ———t———F———F———F———F———F———+

Set to:
|

The

field is:

1lo01]lO0O1ll

01l

-t ———F———F———F———F———F———+———+

DSTADDR (2) : B

Is the logical link destination address.

SRCADDR (2)

: B

Is the logical link source address.

ACKNUM (2)

: BM

Is the number of the last NSP Interrupt
or Link
Service
message
successfully
received
and
a
positive acknowledgment
(ACK)
or
a
negative

acknowledgment
(NAK). = This
field
1is optional.
Its presence is indicated by
bit 15 being
set.
The format for this field is as follows:
et S

Bit:

T et fmm— e
——— +

t————t—————— —_——————— - ————————_————— +

Set to:

QUAL

NUMBER

e-e
—— +

'where:

QUAL (3B) :

NUMBER (12B)

ACKDAT (2) : BM

: B

Is an acknowledgment'qualifier.
0

ACK

NAK

2-7

reserved

Is the

being

number

acknowledged.

the

message
|

Is the number of the last NSP Data Segment message

positive
a
and
received
successfully
acknowledgment (ACK) or a negative
acknowledgment
(NAK).
This
field is optional.
1Its presence is
indicated by bit 15 being

this

field

is as

follows:

The

set.

format

for

Message:

Formats

e +

Bit:

Set

to:

QUAL

122

Page

NUMBER

+————t———————————
- e ——————— +

where:

QUAL (3B) : B

Is an acknowledgment qualifier.
0,1 reserved
2

NUMBER (12B)

: B

SEGNUM

(2)

cross
cross

4-7

reserved

1Is the
being

Is the
format

sub-channel
sub-channel

nUmber

acknowledged.

number of this Link Service
for this field is:

ACK
NAK

the message
|

message.

The

tm———————— tmm—————— +

Bit:

tm———————— e +

Set to:

NUMBER

Fm——————— tmm e
—
+

’BM

Is the Link Service flags.

field

The

follows:

format

for

this

+t-——+—-——t———t———t————————— tm———————— +

Bit:

716151

413

+-——t———t—————— ————————— tmm——————— +

Set

to:

FCVAL

INT

FC MOD

+———t———t————————————— tm——————— +

where:

FCVAL INT (2B)

the

FCVAL

interpretation

data

segment

(2B)

message

count

1l
interrupt
2-3 reserved

FC MOD

field

request

count

Is
the
flow
control
modification.
If FCVAL INT =
0, then this
field
following contents.,

LSFLAGS (EQ)

no
do

change
not send data
send data
reserved

has

the

Message Formats

Page

'If FCVAL INT= 1,
field
1s
ignored
on

FCVAL

(1)

Is the number of Session
|

123

then

this

messages,

Data

0
on transmit
receive,

Control

and

Segment
messages,
or Interrupt messages that
sender of the message can receive in
addition

- those

previously

message.

This

count which

requested

number

1is

added

is maintained by NSP,

the
to

Link Services
the

request

to determine

how

many Session
Control
messages,
Data
Segment
messages,
or
Interrupt
messages
will
be
transmitted via a logical link.

- NOTES

1. If FCVAL INT = 0, the message is a Data Request message.
2.
3.

If FCVAL INT

message.

the

The transmit request count
negative.
form in the

message

for segment

(Negative
values
FCVAL field.)

Interrupt

flow

are presented

control

2's

control, the
no change in

count must
the count.

p051t1ve.

Use

may

complement

1If FCVAL 1is for Session Control message or Interrupt

flow
to be

Request

0 1f

message

there

1is

Message Formats

8.4

;

Page 124

Acknowledgment

message

Acknowledgment Types

There
are three

types

acknowledgment

messages:

Data Acknowledgment message

(Section

8.4.1)

Other-Data Acknowledgment messages (Section 8.4.2)

3. Connect Acknowledgment messages (Section 8.4.3)

8.4.1

has

the

Data Acknowledgment Message - The Data
following

form:

b SR
— bmm—————
— tmmm————— t———— —_———y

| MSGFLG |

DSTADDR |

SRCADDR | ACKNUM |

[ACKOTH]

bom——_—_————— +——————— o

MSGFLG (EX)

————— +

Is the message identifier.
field

The

format

this

is:

'+—-++——-+e——+———+——¥+———+-——+-——+

Bit:

716151

43121110

=t
———
-~
————t———F———+

Set

to:

[

OOl

1101

-ttt ———F———t———t——————+

DSTADDR (2)

: B

Is'the logical link destination address.

SRCADDR (2)

Is the logical link source address.

ACKNUM (2)

Is the number
of the last NSP Data Segment message

successfully
- acknowledgment

(NAK) .

this

This

field

received
and
(ACK) or a negative

field

1is required.

follows:

a
positive
acknowledgment

The format for

m—————————————— o
———— - +

Bit:

et
———
e
—+

Set

to:

QUAL

NUMBER

- ———_——— . +

where:

QUAL

(3B)

Is an acknowledgment qualifier.
0

ACK

NAK

2-7

reserved

Message

Page

Formats

the

Is the number of the last NSP Other

Data

NUMBER (12B)
ACKOTH

(2)

B Is the

number

being acknowledged.

and

received

successfully

acknowledgment (ACK) or a negative

(NAK).

field is optional.

This

set.

indicated by bit 15 being

this

field

Bit:

is as follows:

message

acknowledgment

The

format
—

for

0 |

et —————— e ———— +

Set to:| 1

QUAL

fm————tpmmm————_—————— tm————

NUMBER

e ————— +

where:

QUAL (3B) : B

Is an acknowledgment qualifier.
0,1

reserved

cross sub-channel ACK

cross sub-channel NAK
3
4-7 reserved

NUMBER (12B) : B

Is the number of the message

being acknowledged.

positive

1Its presence 1is

12 | 11

message

| 15 |

125

Message Formats

8.4.2
Other-Data
~Acknowledgment
Acknowledgment
message
acknowledges
messages. It has the following form:

e e Rt

| MSGFLG |

DSTADDR | SRCADDR | ACKNUM

Message
Interrupt

(EX)

Is the message

field

[ACKDAT]

7161

DSTADDR

[

OOl

to:

The

format

Hp I

e skt T

lOIl

1101

SRCADDR (2)

Is the logical link source address.

Link

]

-t
———

this

514131121110

(2)

ACKNUM (2)

Other-Data
Link
Service

Bit:

Set

identifier.

is:

126

—+

tm——————— o —————— - —————— t——————— e ———————

MSGFLG

The
and

Page

the

logical

link destination

Is the number of the last NSP

address.

Interrupt

Service
message
successfully
received
and
a
positive
acknowledgment
(ACK)
or
a = negative
acknowledgment
(NAK).
This
field
1is required.
The

format

for

this

field

fOllOWS'

et —————— Fm e +

Bit:

Set

to:

QUAL

eT+

NUMBER

b L et +

where:

QUAL

(3B)

Is an acknowledgment qualifier.
0
1l
2-7

NUMBER (12B)

(2)

reserved

B Is the

ACKDAT

ACK
NAK

being

number

Is the number of the last NSP Data
successfully
received
and
acknowledgment (ACK) or a negative

(NAK) .

This

field is optional.

indicated by bit
this field is as

acknowledged.

15 being
follows:

set.

the

message

Segment message
a
positive
acknowledgment

1Its presence

The

format

for

'Page 127

Formats

Message

bo
——
+

Bit:

t————t————————— . +

Set to:

QUAL

NUMBER

———— +
——— -

where.:.
(3B)

Is an acknowledgment qualifier.

= WO

QUAL

NUMBER (12B) : B'
|

8.4.3

Connect

message has

Acknowledgment

the

following

form:

-7

reserved
cross sub-channel ACK
cross sub-channel NAK
reserved

Is the

number

being acknowledged.

Message - The

Connect

the

message

Acknowledgment
-

t——————— m———————— +

| MSGFLG

DSTADDR|

+,"“,'.—————— +———————— +

MSGFLG

(EX)

Is the message
field

1s:
R

Bit:

Set to:
DSTADDR

(2)

identifier.

The

format

ek T

5.1

0Ol

e e

311211110

—
————+
mm—pmm
b ———t———t———p——
pmm—fp

toOol

o1l

1101

$mm et m——p———p———
b ——— et —— = ———+

'Is the logiCal link destination address.

this

Message Formats

8.5

Control

There

are

Page

Messages

five types of

control messages:

No Operation messages

(Section 8.5.1)

Connect

Connect Confirm message

Disconnect

Discdnnect Confirm messages (Section 8.5.5)

- 8.5.1

128

Initiate messages

(Section 8.5.2)

(Section 8.5.3)

Initiate messages

No Operation Message

(Section 8.5.4)

- +———————— +

MSGFLG

TSTDATA/|

o ————— o ————— +

where:

MSGFLG

(EX)

the message

‘field

identifier.

The

format

it St

Bit:

Set to:

7161

51413121110

t———t———p———p
b ——— b
—— o ———

ololt1lofl

01l

fm——tm—— b
—e
———

'TSTDATA

any

‘of

1S:

data.

this

Message

8.5.2

The

Page

Formats

Connect Initiate And Retransmitted Connect Initiate
Initiate and the Retransmitted Connect

Connect

have the

following

129

Messages -

Initiate messages

form:

tm—————— +—————————
e —————
e ————
— —— — t————— t————————— b ———————— +

| MSGFLG | DSTADDR| SRCADDR |

SERVICES |

INFO | SEGSIZE | DATA-CTL |

m——————— t—————————t————————— +m—————————— +—————— tm———————— fmm————————
where:

MSGFLG

(EX)

Is the Connect Initiate message

identifier.

format
of this field is:
$m—m

Bit:

Set to:

et —p———p———p———t———+———+

The

—m

5141

31211120

]

e —p———p———f———p———+———+

0Ol

0ol

111110101}

t———t

——t

e — b= ———F———t———+

MSGFLG

(EX)

the

Retransmitted

identifier.
b

Bit:

The

Connect

format of

—pm—m—pmm

this

Initiate

field

message

1is:

e m——f———f———
¢

17161514131

21110]

bmm—tmm—t—
b m
e
———p——— +

Set to;

21110111101

01l

bt —Fm——Fpm——t———F———F———+———+

DSTADDR

Is the destination

(2)

address

will

1logical

1link

address.

This

0 to allow the receiving NSP to

assign a number dynamically.

SRCADDR

number
Is the source logical link address.
This
is assigned by the sending NSP and will be used by

(2)

for

the destination to address all messages
logical link. The value 0 is illegal.

SERVICES

(EX)

The requested services.
1s

The format for this field

follows:
t———t———t———F
==t ———F———f———t———+

Bit:

Set to:

01l

where:

31211120

+
—F
———F———t———+———
———F——
+—-——F==t
pm——

bt m——pm

this

FCcOPT

1 |

—
===+
b ——p———F——

Message

Page

Formats

- FCOPT

(2B)

Are the
0
1l
2

INFO

(EX)

Is the
as

flow control

options.

none
segment
Session

Control message

request

count

request

130

count

reserved

information.

The

format

follows:

for

this

field

1is

fm—m—pmm—p———p———F———p——————F———
¢

Bit:

tmm

Set to:

31|

21110

]

b —————— b ———+———+

VER

t———F———t———F———t———t———t———+———+

_where:

VER

(2B)

Is the NSP version.
0
1
2
3

SEGSIZE

(2)

version 3.2
version 3.1
version 4.0
reserved

Is the maximum size (in byteS) of the

Data

Segment

that

can be

received on

data

this

logical

link.
DATA-CTL

Is the Connect Initiate data field.
The length of
this field is ascertained from the total length of
the Connect Initiate message and consists
of
all
bytes in the message after the SEGSIZE field.

Message Formats

Page 131

following

form:

the

has-

Connect Confirm'MeSSage - The Connect Confirm message

8.5.3

)

——————— Fm——————— t———————— e t—————— ———————— fm———————— +

t——————— e —————— o ———————— e

————— +m————— Fmmm——————— t—————————— +

where:
MSGFLG (EX)

Is the message identifier.

field

is:

Bit:
|

Set

DSTADDR (2) :

(2)

SRCADDR

SERVICES (EX)

this

5141312111740

b ———p———F———t———t———
=== ———+

to:

fmm

format

—pm—— e ——F——————t——————+

7161

The

11011110101l

e m et m

e —p———p———F———h
———+

Is the destination

logical

will
not
be
0.
It
field from the Connect

1link address.

This

is the value
of the SRCADDR
Initiate message.

Is the source logical link address.
This
number
is assigned by the sending NSP and will be used to
address all messages for this logical 1link.
The
value 0 is i1illegal.

BM Are the requested services.
field

$mm

Bit:

The format

follows:
e

for

this

mmm b ———F———p——————t———+

71l

61l

54|

3121110

FCOPT

dm——pm——t———t———t———F———F———F———+

Set to:

[

+t--+t-——+---+-——+--—+-——+-——+—-———+

where:

FCOPT

(2B)

Are the flow control options.

none

segment

Session Control message
request

INFO (EX)

: BM

' Is the information.
as

follows:

Set

count

reserved

The format for this field
.

fmm
e mm— b ——p—m—mm—m—m—d——
—+
| 716 151413121110
]|

Bit:
>
o

request

to:

|
0l
0l
b

m—

—p———p——— b
0Ol

O0O1l

——t—— =
01|

———+

VER

e ——t———t———t———+———+

1is
-

Message

Formats

Page

132

- where:

VER

(2B)

Is
0
1
2
3

SEGSIZE (2) :

DATA-CTL

the NSP version.

(I-16)

version 3.2
version 3.1
version 4.0
reserved

Is the maximum size (in bytes) of the

Data
link.

Segment

that

can be

Is user-supplied data.

received on

data

this

1in a

logical

8.5.4

Page 133

Message Formats

Disconnect Initiate Message - The Disconnect

has the following form

Initiate

message

format

t—————— tm———————— e ——————— - ——————— +m———————— +

+—————— t————————— o ——————— o —————— t—————————

where:

- MSGFLG (EX) : BM

Is the message 1dent1f1er.

field

The

this

is:

F———+
m—pm
e ———t———p———
fm——t———m—

Bit:

Set to:

71615141

0Ol

31211140l

———F———+———+———+

11111101010

f———t—m—tm——pm——tpm——t——————f———+

DSTADDR (2)

: B

Is the logical link destination address.

" SRCADDR (2)

: B

Is the logical link source address.

REASON (2)

: B

DATA-CTL (I-16)
~

two

Dbytes

Session

Control

the remaining

bytes

Session

Control

the

first

disconnect

: B Is

data.

disconnect data.

Message

8.5.5
the

Formats

Page

Disconnect Confirm Message - A Disconnect Confirm

following

form:

$m—————— b ————— e

IMSGFLG

DSTADDR

fm—————— e

——_——

message

134

has

———— o ————— +

SRCADDR

REASON|

b ———— $m—————— +

where:

MSGFLG (EX)

: BM

Is the message identifier.

field

The

1is:

format

this
-

+-—4+———+——f+——4+———+———++f—+———+

Bit:

7161

Set to:

et T

0Ol

5141|311

11l

o0l

21]11]0|

110101

ST EE &

+———+———+———+——f+———+———+-——+———+

DSTADDR (2)

: B

"REASON (2)

Is the logical link source address.

SRCADDR (2)

Is the logical link destination address.

: B

Is the disconnect reason.
NOTES

If REASON

1, the message 1s a No Resources message.

REASON

42,

the message

a Disconnect

REASON

41,

the message

a No Link Terminate message.

Complete message.

APPENDIX

LOGICAL LINK ADDRESS ASSIGNMENT/DEASSIGNMENT,

is a 16-bit value.
A logical link address

When an NSP module opens

When an NSP module closes a

it assigns a logical link address.
port, it deassigns a logical link address. The algorithm that assigns
and deassigns these addresses 1s implementation-dependent. There are

port,

It must not assign

concurrently,

and

given

two requirements for this algorithm:

1l6-bit

address

two

ports

periodaddress for a long
It must not reassign a given 16-bit
|
|

following its deassignment.

n, algorithm should'operate
In additiothe
trading

memory,

reassignment.

off

the

amount

with

memory

amount

modest

for

period

the

The algorithm described in this appendix is a sample algorithm that
of NSP is required to use
meets these requirements. No implementation
two
the
meets
that
algorithm
Any
this algorithm, however.
algorithm
sample
The
.
acceptable
is
above
stated
requirements
of outstanding, assigned link addresses.
restricts the number

A.1

INTERFACE TO THE ALGORITHM

The sample algorithm is implemented by a
calls:

module that

accepts

three

one to assign a link address, one to deassign a link address,

and one to

initialize the module.

The following routine assigns a link address.
GET-ADDRESS

returns:

success - a link address 1is returned

failure - too many link addresses currently assigned

The following routine deassigns a link address.
RELEASE-ADDRESS

(address)

LOGICAL LINK ADDRESS ASSIGNMENT/DEASSIGNMENT
address:

the

link

returns:

success

following

routine

deassigned
|

failure
The

address

Page A-2

link

address

initializes

the

was

not

assigned

algorithm module.

INITIALIZE-ADDRESS

NSP

the
'NSP

calls

this routine during NSP
algorithm module to meet the
initializations.

A.2

DATA STRUCTURES

This

algorithm

forms

link

random

initialization.
The routine
second requ1rement above even

addresses

part

index

bits

the

following

allows
across

form:

part

bits

where:

r+i
= 16

No two concurrently assigned link
value 1n the low 1 bits,
Furthermore,

be assigned

the

algoflthm

concurrently

addresses

restricts

will

contain

the

same

addresses

that

can

These

are

|
the

open ports

number

to:

2°1-1
The

data

the

following.
1.

base

consists

two

vectors

and

three

Boolean

vector

INUSE

This vector contains 2”i bits.
There
possible value in the index part of a
A bit

(i.e.,

The
2.

bit

Vector

varlablese

set

1is

"true"

in the lower

set

"false"

the

is
one
bit
link address.

corresponding

index

for

1in

each

use

i bits of an assigned link address).
otherwise.

RANDOM

This vector contains 27i
entries,
each
r
bits
wide.
An
element
of
the
vector contains the random part of the last
lirtk address assigned with the index part equal to the
1index
of this element in the vector.

Page A-3

LOGICAL LINK ADDRESS ASSIGNMENT/DEASSIGNMENT
Variable NUMBER-ASSIGNED

This variable contains the number of link addresses currently
|
a value in the following range:
It has

assigned.

O <= NUMBER-ASSIGNED <= 27i-1

When NUMBER-ASSIGNED = 271-1, then no more link addresses may
'

be assigned.

Variable

INDEX

This variable contains the 1ndex value_portion
link address that was assigned.

the last

Variable TEMP

value
'This variable is used to temporarily hold the index
1in
and
gned
deassi
being
is
that
address
1link
a
portion of
module

A.3

initialization.

ALGORITHM OPERATION

high-level
This algorithm operation 1is represented in the same the
body of
language,- that was used to represent NSP's operation 1in
|

this document.

GET-ADDRESS:

If (NUMBER-ASSIGNED < 27~i-1) then
NUMBER-ASSIGNED <-- NUMBER-ASSIGNED + 1
while (INUSE(INDEX) true) do
INDEX <-- INDEX + 1 (mod 271)
|
Endwhile

RANDOM( INDEX) <-- RANDOM (INDEX) + 1 (mod 27r)
INUSE(INDEX)‘<—— true

random part of link address <-- RANDOM(INDEX)
index part of link address <-- INDEX

return success
Else

return
Endif

failure

RELEASE-ADDRESS:

TEMP <-- index part of the link address
If

(INUSE(TEMP)

true

and RANDOM(TEMP) = random part of link address) then

INUSE(TEMP)

<-- false

NUMBER-ASSIGNED <-- NUMBER-ASSIGNED - 1
return

Else

return

success

failure

LOGICAL LINK ADDRESS ASSIGNMENT/DEASSIGNMENT

Endif

INITIALIZE-ADDRESS:
TEMP

<--

While (TEMP < 2~i) do
INUSE(TEMP) <-- false
|
RANDOM(TEMP) <-- random number

TEMP <-—- TEMP +

Endwhile
INDEX

<--

|
random

NUMBER-ASSIGNED

number
<--

(mod

2A1)

(mod

2Ar)

Page

A-4

APPENDIX

SEGMENTATION MODULE EXAMPLE

supports

the

requires the addition of

the

removed from

the

The model

This appendix models a segmentation module.

queuing of multiple outstanding transmit requests for each port.

B.1

DATA STRUCTURES

To support this model,
1items:

following

each port

Port Additions

1. A request queue head.
2.

A segment queue head.

The segment number of

A Boolean flag to indicate if the next segment placed on “the
segment queue will be a beginning-of-message segment (initial

the

last

segment queue (initial value = 0)

‘value = true).

segment

This model also requires a pool of queue control blocks to hold
information about queued transmit requests and outstanding segments.

When a transmit request

from

Session

Control

1is

the

segmented,

each

accepted

segmentation module, a queue control block is added to the request
|
queue for the port. It contains the following information:
Request Queue Control Block
Buffer descriptor from the request.
1.
Xmtflag from the request.
2 .

3.
4.

Highest segment number corresponding to the request.
Status ("incomplete” or "complete").

When the data from

single

transmit request

1is

segment is assigned a queue control block that is added to the segment
queue for the port. Each segment queue control Dblock <contains the
following

information:

SEGMENTATION MODULE EXAMPLE

Segment

Control Block
Buffer descriptor for
End-of-message flag.

2.,

the

segment.

|
Beginning-of-message flag.
Segment number assigned to

3.
4,

queue

pointer

information
finding the
on
each
block.

B.2

Page B-2

Queue

The

cells

required

1in
the
port
are
first control block

queue,

and

the

segment.

these

blocks

and

the

queue

head

not described but are assumed to allow
in each queue, the last control ~block

control

block

queued

after

given

control

OPERATION

DATA-XMT

This routine operates as follows.
There

must

queue
request

queue

queue.

The

length

control

segment

enough queue control blocks
Dblock
pool
to queue one
and

one

total

number

the

transmit
queue)
plus

buffer

available
block

blocks

required

divided

the

from
the

port's

segment

equal

SIZEseg

(for

one
(if there is a remainder from
previous division) plus one
(for
the
request
queue).
there
aren't
enough
blocks
available
from
the pool,
DATA-XMT call is returned as "buffer not queued."
If

the

port's
the

the

the
If
the

DATA-XMT

call is not rejected, add one
control
block
request
queue.
Store
the
buffer
descriptor and
values from the call in the block.
Set the status to

to
the
xmtflag

"incomplete."
Add

control

block

descriptor
for
the
the DATA-XMT call and
length
from
the
beginning-of-message
beginning-of-message
segment

the

number

queue

the

plus

segment

one

Otherwise set the segment
descriptor plus one.

port

the

segment

number

(if

there

number

Add the remaining control blocks

queue.

the

The
transmit

perhaps,

the

buffer

buffer
last is

queue.

The

buffer

control block contains the address from
a length equal to the
minimum
of
the
call
and
SIZEseq.
Set
the
flag
to
true
only
1f
the
flag
in
the
port
is
true.
Set the

descriptor

(if

the

1is

that

any)

preceding

contained

the

block

block).

the

segment

reflects the segmentation of
1into
segments.
Each
segment
except,
as long as the previous segment.
Assign

each block a segment number equal to that of
the
preceding
block
on
the
queue plus one.
Clear the end-of-message and
beginning-of-messa
flags
ge of each
block,
except,
perhaps,
the last one.
The last block has the end-of-message flag set
only if the xmtflag value
1in
the
DATA-XMT
call
indicates

Page B-3

SEGMENTATION MODULE EXAMPLE
end-of-message.

Give the request queue control block queued

1in

step

segment number of the last block on the segment queue.

the

XMT-POLL

This routine examines the first block on the request
queue.
If the
Return the
the block from the queue.
remove
"complete,"
is
status

Give a "transmit complete"” return with the buffer
block to the pool.
If the status is not "complete," give a
from the block.
descriptor
"no transmit

complete"

return.

\\\///l

GET-SEGMENT

This routine examines the segment

matching

segment number.

and beginning-of-message

queue

find

The buffer descriptor,

flag are returned.

éntry

with

flag,
end-of-message
-

ACK-SESSTION-CONTROL

This routine operates as follows.
1.

Examine the first block on the segment queue.

number
4096)

in the block,

go to step 3.

Otherwise,

go to step 2.

Remove the block from the queue and return the block

pool.

Store

Go to step 1.

If the segment

from the call is less than the segment number (modulo

Examine the request queue.

containing

to the

the segment number from the block in the port.
Mark every

entry

the

queue

a segment number less than (modulo 4096) or equal

to the segment

number

from

the

call

"complete."

Make

return.

NM
This routine
entry with a
to the entry
the
counts

from the
segment queue
identifies the entries on the
segment number equal to the first argument in the call up
It
equal to the second argument in the call, inclusive.
number of these entries that have the end-of-message flag

set and returns this value.
LAST

1f
'Return the segment number of the last block on the segment = queue,
the
from
Otherwise, return the segment number
such a block exists.
port.

APPENDIX
REASSEMBLY

MODULE

This appendix contains a model of a

EXAMPLE

reassembly

module.

requires

the

This

model

supports the queuing of multiple outstanding receive requests for each
port.
It does not support the use of either cache or commit buffers.

C.1

DATA STRUCTURES

To support

following
Port

this

model,

items:

each

port

addition

the

Additions

A request queue head

A variable (FLOWreass) used to conta1n changes to the
count for the port (initial value = 0)

A variable

(FLOWhigh) to contain the

A Boolean

variable

(modulo
4096)
stored
(initial value
= 0)

1in

session

(FLOWdiscard)

segments are to be discarded

highest

segment

request

number

control receive buffer
|

indicate

(initial value =

false)

received

This model also requires a
pool
of queue
control
blocks
to
hold
information
about.
queued
receive
requests.
When a receive request
from session control 1s accepted by the
reassembly
module,
a
Qqueue

~control block
the following

is added to the
information:

request queue

for

the port.

contains
|

Request Queue Control Block
"o
o

Buffer descriptor from the request
Temporary

multiple

buffer

segments

descriptor

into

the

Rcvflag from the request

same

handle

the

receive buffer

reception

REASSEMBLY MODULE

C.2

EXAMPLE

Page

Status
("incomplete,"
truncation,"
"no
EOM -- truncation").

"EOM -- no
EOM -- no

truncation, "
truncation,"

C-2

"EOM -"no

OPERATION

In the fOllowing descriptions, the checking for invalid port states is

not
described
specification.

since

assumed

clear

from the

body of

the

DATA-RCV

This

routine operates

follows.

If no truncation was specified and
NSPbuf, reject the call.

If no more queue control blocks

the buffer
-

are

smaller

than

available,

reject

the

call.

Otherwise, store the
<call
parameters
1n
a
queue control
block.
Set
the
temporary buffer
descriptor equal to the
request buffer descriptor.
Add
the
block
to
the
receive
request

queue.

1If rcvflag indicated no truncation,
1increment
FLOWreass
by
one.
Otherwise, compute the smallest integer greater than or
equal to the length of the receive buffer divided by
NSPbuf.
This 1is how many segments will fit into the buffer.
Add the
result to FLOWreass.
|
|

RCV-POLL

If
the
state
of
DISCONNECT-COMPLETE,

the
port
1S
DISCONNECT-NOTIFICATION,
CLOSE-NOTIFICATION,
set
the
status of all
"incomplete" control
blocks
on
the
request
queue
to
either
"no
EOM -- no
truncation" (if rcvflag was "no truncation allowed") or "no
EOM -- truncation” (if rcvflag was "truncation allowed").

Examine

the

first

block on the

receive queue.

has a value

other

than
"incomplete," remove the block from the queue.
to the control block pool.
Return the request buffer
status value to Session Control.

Return the block
descriptor
and
|
|

If the return block has the value
"incomplete,"
returned” indication to Session Control.

give

'SPECULATE-NUMBER
Return the contents of FLOWreass and clear FLOWreass.

"no

buffer

REASSEMBLY

MODULE

EXAMPLE

Page

C-3

COMMIT-NUMBER

Return the contents of FLOWhigh.
STORE-SEGMENT

The
description
language.
The

end-of-message

this
routine
wuses
a
colloquial,
NUMBER and EOM represent the segment

terms

flags,

respectively,

passed to this

routine by the data

receive process.

(NUMBER = FLOWhigh + 1) then
Find the first "incomplete" queued

(such a

high-level
and

number

request

exists)

receive

request

then

FLOWhigh <-- FLOWhigh + 1
If (rcvflag = "no truncation") then
Put received data in front of buffer
Set status using EOM
Else
If (FLOWdiscard) then
If (EOM set) then
FLOWdiscard <-- false
Else
‘
FLOWreass

<--

FLOWreass

Endif
Else

Put data

(that will

fit)

in buffer

Adjust temporary buffer
If (data fit in buffer)
If (EOM set) then

descriptor
then

Calculate
FLOW

space

reass

<--

Set status
Endif
|
Else
|
Set status to

(EOM not
FLOWreass

loss

to "EOM
o
"EOM

set)

(NOTE

FLOWreass

reflect storage

space loss
truncation"

|
truncation”

then

<-- FLOWreass

FLOWdiscard
Endif
Endif
Endif
Endif
Endif
Endif

(NOTE
to

<--

true

NOTES

Use the temporary buffer descriptor.

2. The space loss 1s equal to the number
of segments
requested
to fill the buffer, but for which
receive space due to
the
impending
return
partially filled.
»

that

were

there will be no
of
the
buffer

TRANSMIT

APPENDIX

ALLOCATION

MODULE

EXAMPLE

This appendix contains a model of a transmit allocation module.

D.1

DATA

STRUCTURES

This model requires a
1list
structure.
Each
element
contains
a
port
identifier.
This list must be large
one element for each port that NSP can handle.

D.2

PRIMITIVE

This model
List

assumes that

the

functions

described below are

available.

Functions

element

element,

removed

The

list
hold

FUNCTIONS

Manipulation

in
the
enough to

can

be added
to

selected

from

contents

list.

either

1ndex

entry

list

entry

can

range

can

contents,

can

the list.

the

first

read.

Random Number Generation
A

D.3

random number

selected

obtained.

OPERATION

The following description of the transmit allocation module
uses

high-level,

ALLOCATE

(port

colloqulal

language.

1d)

) Add an element with port id to the list.

operation

TRANSMIT ALLOCATION MODULE EXAMPLE
CHECK-ALLOCATE
If

(port

id =

return

Page

(port id)
contents of

first

list

success

entry)

then

Else

return

Endif

failure
|

DEALLOCATE (port id)
Remove the list
Call REALLOCATE

REALLOCATE

entry containing

(port

port id

id)

(list not empty) then
Get random index (NOTE)
.
Swap first and indexed entries
Endif

NOTE

This function obtains a random number in
the

range

(1,

length of

list).

D-2

APPENDIX

REVISION HISTORY

This

appendix-describes the differences from NSP 3.2.1 to NSP 4.0.
Phase III and Phase IV NSP do net send NAKs

Several fixesvto Section 6.4.2 and 6.8.
The variable "NUMsent" was added to the Session Control

Port

of the highest numbered Data Segment
indicate the number
to
Changes were made to the
NSP.
local
by
sent
message
the Data Transmit Process to
and
routine
DATA-ACK"
"PROCESS|

accomodate the new variable.

Change the names of the Network Services Layer and Transport
Layer to the End Communications Layer and Routing Layer,
|

respectively.

Addition of the "tryhard" parameter to the Routing Layer
interface and a procedure for setting the TRYHARD variable in
the Session Control Port data base. This is a local change
only and does not affect the NSP protocol.

Replace the "channel" parameter with "circuit” and

"nexthop"

d Routing version 2.0.
parmaters as requireby

Changes

the

connect procedure

allow

for

the

will

1ignored

old

retransmission of Connect Initiate messages, with new message
SO
message,
Initiate
types for retransmitted Connect

retransmitted

implementations.

"connects"”

This is an upward compatible change.

Changes,to the flow control procedures and message formats to

‘permit

cross

sub-channel

piggybacking of acknowledgments.

Cross sub-channel acknowledgments are not sent, except when
4.0, so this is an upward
communicating with an NSP Vs.
compatible change.

APPENDIX

GLOSSARY

confidence

that

An NSP variable (CONFIDENCE)

the

1indicates

pfobable’

connectedness of the physical network supporting a logical link.

data flow

The

movement

data

from

source

Session

Control

NSP transforms data from Session
destination Session Control.
form before sending 1t
network
a
to
Control transmit buffers
NSP retransforms the data at the
across a logical 1link.
form to 1its receive buffer form.
network
destination from its
(full-duplex) on a logical link.
s
direction
Data flows in both

datagram

»>

—

ng control information, that is passed
A unit of data, includiNSP
transmission to a destination system.
for
to the Routing Layer

becomes

When Routing adds its route header information, the unit
a packet.

Data Link

‘The DNA layer below the Routing Layer. The modules in the Data
Link Layer manage physical channels and maintain data integrity.
delay factor

An NSP parameter (NSPdelay) that is multiplied by
round

the

estimated

trip delay time to determine the appropriate value for the

time to retransmit certain NSP messages.
delay weight

)

An NSP parameter (NSPweight) that is

wused

calculate

new

value of the estimated round trip delay. The old round trip
factor to
delay is weighted by a function of this statistical
k

GLOSSARY

Page F-2

calculate
the
new round trip delay.
If the delay weight is
high, the retransmit time changes slowly.
If the weight
1is
low,
the
observed
round
trip
time
can change quickly if
observed round trip delays have a wide
variance,
and
thus
retransmit

time

delay weight

can

change

rapidly.

The

set

the
the
value for

default

Disconnect Confirm
The
The

NSP No Resources, Disconnect Complete, and No Link
messages.
REASON
field
1in the Disconnect Confirm message (Section 8)

indicates which message
error

applies.

control

The

NSP function that insures the delivery of
consists
of an acknowledgment mechanism.

NSP data

messages.

flow control
The NSP function that coordinates the flow of data on
a
link
in
both
directions,
from
transmit
buffers
to
buffers, in order to minimize communications overhead.

logical
receive

inactivity timer
A timer that,
Data
Request
enters the

message
purpose

upon expiration, causes NSP to attempt
to
send
a
message.
NSP starts this timer when a logical link

RUN/RUN

for
of

state.

that

the

Whenever

NSP

receives

1link,

NSP

restarts

this

logical

timer

provide

activity

for

the

Data

Request

timer.

logical

The
1link

so that
NSP
can
determine
the
probable connectedness of the
physical network supporting the link.
The value for the timer is
an NSP parameter (TIMERinact).
-

Link

Service
The

NSP messages

messages

logical

are

the

that

carry

flow

Data

Request

and

control
the

information.

Interrupt

Request

These

messages.

link

A virtual channel between two Session Control implementations
or
between
two
components
of
one Session Control implementation.
NSP's major function is the creation and destruction
of
logical
links.
|
|

logical 1inkAidentification
A
unique
32-bit
number
describing
a
logical
link.
This
identification
consists of the two 16-bit addresses of the ports
at

each end

the

link.

GLOSSARY

Page F-3

Network Management

The DNA layer directly

above

the

Session

Control

Layer

that

enables
operator
control
over and
observation
of network
parameters
and
variables.
Network
Management
also
provides
down-line loading, up-line dumping, and testing functions.
node descriptor

A
collection
of
variables
and
counters
pertaining
to
communications with a particular node.
Some of the variables and
counters are
the
estimated
round trip delay,
traffic
usage
counters,

and

error

counters.

Other-Data
The NSP Data Request, Interrupt Request, and Interrupt
messages.
These
are
all
the
NSP
data messages other than Data Segment.
Because all Other-Data messages move 1in the same data subchannel,
it is sometimes useful to group them together.
port

A collection of control variables
and
parameters
for managing
logical
1links.
Each logical link has a port at each end.
Each
NSP at each node has a numer of available
ports.
When
Session
Control
requests
a logical link or requests a port be opened to
receive
an incoming connect request,
NSP
allocates
a
port
1if
sufficient resources are available.
|
reassembly

‘The ordering of received
sequence

request

for placement

data

segments by

into Session Control

NSP

into

numbered

receive buffers.

count

This term has two different
definitions
in
the
document.
1)
Variables
(FLOWrem.dat
and
FLOWrem.int) that
NSP
uses
to
determine when to send data.
2)
Values
sent
1in
Link
Service

messages.

The

flow

control

mechanism adds

the

request

counts

received in Data Request and Interrupt
Request
(Link
Service)
messages (definition 2, above) to the request counts it maintains
(definition 1, above) to determine when to send data.

retransmission

The

resending

acknowledged

NSP's

error

within

NSP
a

data

messages

that

certain period of

control mechanism.

time.

have

This

not

been

is part of
4

retransmission counter

An NSP variable (COUNTretrans) that contains a count
timeouts

for Connect Confirm,

Disconnect

Initiate,

message

Data Segment,

GLOSSARY

Page F-4

Link Service, and Interrupt messages. NSP compares this variable | d>

with
the
variable.
retransmit

retransmit

threshold

calculate

(NSPretrans)

equal

the

maximum

successive
times
a
retransmission
occurs
received acknowledgment before NSP
decides

network supporting

retransmit

round

the

confidence

number

with no intervening,
that
the
physical

a logical link has failed.
NSP
with the retransmission counter

threshold

value .of

trip

confidence

threshold

An NSP variable

the

compares

the
determlne

varlable.

delay

NSP

estimated

parameter (NODEdelay)
time

message.

This

Section

4.7.6.

for

parameter

that

acknowledgment
is

calculated

represents
to be

the

received

formula

current
for

an NSP

described

,)
"

1in

segment

The

data

carrled in a
Session Control

from

Data

Segment message.
transmit buffers into

transm1551on by Routing.

NSP divides the data
numbered segments for

segmentatlon

The

d1v151on

into

normal
segments

numbered

data

for

from Session Control transmit buffers
transm1551on over logical l1nks.

Session Control
The DNA layer directly above
system-dependent
aspects of

NSP.
Session
Control
defines
the
logical link communication.
Session

Control provides functions such as name to

process

address1ng,

and

some

address

systems, access

translation,

control

sSubchannel
A logical

messages

two

communications

defined
are

types

different

path within a logical link that
of NSP data messages.
Because Data

category
handled

differently

messages

subchannels.

can

from

Other-Data

thought

handles

Segment

messages,

traveling

the

two

Routing
The

DNA layer d1rectly below NSP that provides NSP with
routing,
congestion control, and packet lifetime control services.

DECnet Digital Network Architecture Phase IV
NSP Functional Specificatio

AA-X439A-TK

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