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Document:	Data Access Protocol Functional Specification
Order Number:	AA-K177A-TK
Revision:	000
Pages:	106
Original Filename:	http://decnet.ipv7.net/docs/dundas/aa-k177a-tk.pdf

OCR Text

Order No. AA-K177A-TK

DECnet
DIGITAL Network Architecture
Data Access Protocol
Functional Specification
(DAP)
Version 5.6.0

ill

DECnet
DIGITAL Network Architecture
(Phase 11.1)
Data Access Protocol
Functional Specification
(DAP)
Order No. AA-K177A-TK

Version 5.6.0

October 1980

This document describes the features, message formats, and
operation of the Data Access Protocol (DAP). DAP provides
standardized formats and procedures for accessing and passing data between a user process and a file system existing in a
network environment. It assumes a controlled conversation
path provided by the network system. In DECnet, this path Is
created by the Session Control and Network Services Protocols and their associated interfaces.

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

digital equipment corporation magnard, massachusetts

First Printing, October 1980

This material may be copied, in whole or in part, provided that the
copyright notice below is included in each copy along with an
acknowledgment that the copy describes the Data Access Protocol
developed by Digital Equipment Corporation.
This material may be changed without notice by Digital Equipment
Corporation, and Digital Equipment Corporation is not responsible for
any errors which may appear herein.

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
DE C
PDP
DECUS
UNIBUS
COMPUTER LABS
COMTEX
DOT

DECCOMM
ASSIST-11
VAX
DECnet
DATATRIEVE

DECsystem-10
DECtape
DIBOL
EDUSYSTEM
FLIP CHIP
FOCAL
INDAC
LAB-8
DECSY STEM- 2 0
RTS-8
VMS
IAS
TRAX

MASS BUS
OMNIBUS
OS/8
PHA
RSTS
RS X
TYPESET-8
TYPESET-11
TMS-11
ITPS-10
SBI
PDT

CONTENTS

Page
INTRODUCTION
FUNCTIONAL DESCRIPTION
DAP Functions
Relationship to the DIGITAL Network Architecture
Generic Model
MESSAGE FORMATS
Notation
General Message Format
Configuration Message
Attributes Message
Access Message
Control Message
Continue Transfer Message
Acknowledge Message
Access Complete Message
Data Message
Status Message
Key Definition Attributes Extension Message
Allocation Attributes Extension Message
Summary Attributes Extension Message
Message
Date and Time ~ttributes~xtension
Protection Attributes Extension Message
Name Message
Access Control List Attributes Extension Message
FILE ORGANIZATION
Types of Files
Record Formats and Attributes
Handling Stream ASCII
Conversions
Data Formats
Fixed-Length Records
Variable-Length Records
Variable with Fixed-Control Format Records
ASCII Stream
Supported Data Types
ASCII
EBCDIC
Image
Compression
OPERATION
Setting up the Link
Errors in the Setup Sequence
Setup Sequence
Transferring Data over the Link
Sequential File Retrieval
Sequential File Storage/Append
Record Retrieval
Record Store
Append to Existing File
Deleting a File
Command/Batch Execution Files

Renaming a File
iii

CONTENTS (Cont

Page
Extending Files
Display Attributes
Directory List
Rewind Data Stream
Truncate File
Free Buckets
Space Forward or Backward
Flush 1/0 Buffers
Deleting a Record
Find
Update
Wildcard Operations
Wildcard Sequential File Retrieval
Wildcard File Deletion
Wilcard File Rename
Wildcard Command File Execution
Closing a File and Terminating Data Streams
Terminating a Logical Link
File Security, Integrity and Protection
Access Control
Data Integrity
DAP-Based Applications Written by DIGITAL
Access Control and Accounting for DAP-Based
Applications
APPENDIX A
APPENDIX B
P 1
B.2

USER IDENTIFICATION MESSAGE
REVISION HISTORY
Version 1.0 to Version 4.1
Version 4.1 to Version 5.6

GLOSSARY

FIGURES
FIGURE 1 Interrelationship of DNA Layers
2 Typical DAP Message Exchange (Sequential File
Retrieval)

TABLES
TABLE

1 DAP Messages
2 MACCODE Field Values
3 MICCODE Field Values for Use with MACCODE Values of 2,
10, and 11 Octal
4 MICCODE Field Values for Use with MACCODE Values of 0,
1, 4, 5, 6, and 7 Octal
5 MICCODE Field Values (with MACCODE Value of 12 Octal)
6 Responses to Setup Message Errors

4
32
33

39
44
61

1.0

INTRODUCTION

This document describes the functions, operation, and message formats
of the Data Access Protocol (DAP). The document is primarily intended
to assist those who implement DAP in understanding how DAP functions
within
a
system.
The
document
does
not address specific
implementations.
DAP performs remote file access via a file system such as Record
Management Services (RMS)
Unit Record Devices and terminals can be
accessed if supported by a file system. When Unit Record Devices and
terminals are supported by a file system in a device-dependent manner,
the device control features peculiar to the individual devices are not
supported by DAP.

DAP is one of the protocols of the DIGITAL Network Architecture (DNA).
DNA models the software (or hardware) for DECnet implementations.
DECnet is a family of software modules, data bases, and hardware
components typically used to tie DIGITAL systems together for resource
sharing, distributed computation, or remote system communication.
DNA is a layered structure. Modules in each layer perform distinct
functions.
Equivalent modules within the same layer in both the same
and different nodes communicate using protocols.
A node is an
implementation of the Session Control layer (Section 2.2).
Usually a
single computer is associated with one node.
Protocols are the
messages exchanged by modules and the rules governing the message
exchanges. Modules in functionally different layers of DNA interface
using either subroutine calls or a system-dependent method.
A glossary at the end of this document defines many DAP terms.
Other DNA Phase I11 functional specifications are:

DNA Digital Data Communications
Message
Protocol
(DDCMP)
Functional Specification, Version 4.1.0, Order No. AA-K175A-TK
DNA
Maintenance
Operations
Protocol
(MOP)
Specification, Version 2.1.0, Order No. AA-K178A-TK
DNA Network Management Functional Specification,
Order No. AA-K181A-TK
DNA Network Services (NSP) Functional
3.2.0, Order No. AA-K176A-TK
DNA Session Control Functional
Order No. AA-K182A-TK

Functional

Version

2.0.0,

Specification,

Version

Specification,

Version

DNA Transport Functional Specification, Version 1.3.0,
AA-K180A-TK

Order

The following overview document for these specifications
introduction to the structure and functions of DNA.
DNA General Description, Order No.

AA-K179A-TK

1.0.0,

No.
an

2.0

FUNCTIONAL DESCRIPTION

The Data Access Protocol is an application level protocol.
Its
primary purpose is to permit remote file access within the DECnet
environment independently of the 1/0 structure of the operating system
being accessed.

2.1

DAP Functions

Within DECnet, DIGITAL operating systems can employ DAP to provide the
following remote file access functions:
Retrieve a file from an input device.
Store a file on an output device.
Provide ASCII file transportability between nodes.
Provide error recovery.
Allow multiple data streams to be sent over a logical link.
Command file execution and submission.
Provide for random access of records in a file.
Provide for file deletion.
Rename files.
List directories.

2.2

Relationship to the DIGITAL Network Architecture

The DIGITAL Network Architecture provides a modular design for DECnet.
Its functional components are defined within eight layers which are
described below. Each layer performs a well-defined set of network
functions (via network protocols) and presents services to the layer
above it:
User layer. The User layer contains all the user-supplied
It is the highest layer in the DNA structure.

functions.

Network Management layer. The Network Management layer contains the
modules
that provide user control over and access to network
parameters and counters.
Network Management modules also furnish
down-line loading, up-line dumping, and testing functions.
Network Application layer. The Application layer supports the various
user services and programs that utilize the network facilities. These
services and programs must utilize the network communication mechanism
provided by the Session Control and Network Services layers. DAP
resides within the Application layer.
Session Control layer.
The Session Control layer defines
system-dependent aspects of logical link communication.

the

Network Services layer.
The Network Services layer provides the
mechanism
that
permits
node-to-node
communications
and
process-to-process communications between processes in the same or
different nodes.
It provides a logical link service and a datagram
service to the network.
Transport layer. The Transport layer provides a mechanism for the
network service layer to send a unit of data (a packet) from any node
in the network to any other node in the network.

Data Link layer. The Data Link layer controls the physical
operation to ensure both data integrity and sequentiality.

link

Physical Link layer. The Physical Link layer, the lowest layer,
consists of device specific modules that provide the interface to the
communication hardware.
Figure 1 shows the interrelationship of the DNA layers.

nuo on Control ~ o d u l i

Notwork Services Moduli

e/
Transport Modules

D m Link Moduli
I

Physical Link Moduli

I
I

Dm Link L w w

Hi*

Link L-

Horizontd mow* show direct accen for control and axnni~tionof paruneton, countere, te. Vartid UI
Wrvd arrow* show interfw* b Ã § t w layers for normal usor opÃ§rationsuch a film Â ¥ c e ~down-liw
t
load
up-Un* dump, and-to-Ã§nlooping, Ã§nlogic*! link u q a .

Figure 1

Interrelationship of DNA Layers

2.3

Generic Model

As an aid toward understanding the Data Access Protocol, this section
contains a generic model. This model consists of a summary of the DAP
messages (Table 1) and a typical DAP message exchange sequence
illustrating how DECnet sequential file retrieval is accomplished
between two dialogue processes (Figure 2)

For a more detailed description of the DAP message formats and
protocol operation, refer to Sections 3.0 and 5 . 0 , respectively.

the

Table 1
DAP Messages
-

Message

Function

Configuration

Exchanges
system
capability
and
conÂiguration
information
between
DAP-speaking processes.
This message is
sent
immediately
after
a
link
is
established. It contains information about
the operating system, the file system,
protocol version, and buffering ability.

Attributes

Provides information on
how
data
is
structured in the file being accessed. The
message contains
information
on
file
organization, data type, format, record
attributes, record length, size, and device
characteristics.

Access

Specifies the file name and type of
requested.

access

Control

Sends control information to a file
and to establish data streams.

system

Continue-Transfer

Allows recovery from errors.
Used for
retry, skip, and abort after an error is
reported.

Acknowledge

Acknowledges access commands and control
connect messages used to establish data
streams.

Access Complete

Controls termination
access.

Data Message

Transfers the file data over the link.

Status

Returns status
conditions.

Key Definition
Attributes Extension

Specifies
files.

Allocation
Attributes Extension

Used when creating or explicitly extending
a file to specify the character of the
allocation.

key

and

file

and

information

definitions

for

stream

error
indexed

(continued on next page)

Table 1 (Cont.)
DAP Messages
Function

Message
Summary
Attributes Extension

Returns summary information about file.

Date Time
Attributes Extension

Specifies
the file.

Protection
Attributes Extension

Specifies the file protection code.

Name

Sends name information when renaming a file
or obtaining a directory listing.

Access Control
List Attributes
Extension

When creating a file, this message is used
to specify the access rights users are
granted for access to this file.

User Node Message
Description

time-related

information

about

Remote Node Message
Dwiption

Meiuges
Configuration Message

Configuration Information
(e.g., Buffer Size, OS, File
System DECnet Phase No.,
and DAP Version No.)

Configuration Message

Attributes Message
File Characteristics
(e.g., Type, BIk Size
and Record Size)
Access Message
Access Request

Configuration
Information
Returned

Attributes Message

Set up Data Stream

Actual File Characteristics Returned
Acknowledge Message
File Opened
Control (Initiate Data Stream)
Message

Acknowledge Message
Data Stream Established

Control (Get) Message
Request Start of Data
Transfer and Mode of
Transfer

Record 1
Data Sent in Records

4
Â

Â
Â

Record N
Status Message
End-of-File Indicated

Access Complete Message
b

Request to Terminate
Access Complete Response

Request Completed Successfully

Figure 2

Typical DAP Message Exchange (Sequential File Retrieval)

3.0

MESSAGE FORMATS

3.1

Notation

The following notation is used to describe the DAP messages:
FIELD (LENGTH) : CODING

Description of field.

where :
FIELD

Is the name of the field being described.

LENGTH

Is the length of the field, which can
one of four ways:

indicated

A number meaning number of 8-bit bytes (octet).

A number followed by a "B" meaning
bits.

The letters "EX" meaning extensible field.
Extensible
fields
are of variable length
consisting of 8-bit bytes
in
which
the
high-order bit of each byte denotes whether the
next byte is part of the same field. A 1 means
the next byte is part of this field and a 0
denotes the last byte. Extensible fields are
for bit maps only. Seven bits from each octet
are used as information bits.
The notation
EX-n
means an extensible field where the
maximum length of the field is n bytes.

number

NOTE

The
bit
definitions
define
information
bits after removing
extension bits and
compressing
remaining bits.
4.

CODING

the
the
the

The letters "I-n" means this is an image field,
with n being a number that specifies the
maximum length of the field in 8-bit bytes.
The image is preceded by a 1-byte count of the
length of the remainder of the field.
Image
fields are variable in length and may be null
(count=0). All 8-bits of each byte are used as
information
bits.
The
meaning
and
interpretation of each image field is
as
defined with that specific field.

Is the representation type used, where:
A = 7-bit ASCII
B = binary
BM = bit map (in which each bit has a specific
meaning)

The following rules apply to the notation:
If length and coding are omitted, field represents
of subfields specified in the description.

number

Any bit or field described as "reserved" shall be zero unless
otherwise specified.
All fields are presented to the Session Control Protocol with
the least-significant byte first.
In an ASCII field, the
left-most character is contained in the low-order byte.
All numbers are in decimal unless otherwise specified.
When default values are defined for fields in DAP messages,
the values will be used only if that field is absent from the
message. There are two ways in which fields within DAP
messages can be omitted so the default can be used:
a.

A field that appears under a MENU may be
setting the corresponding MENU bit to zero.

Trailing fields in DAP messages may be omitted if they
are not needed or if the default value can be used. If a
MENU field is truncated in this way, its value is zero
(which means all the fields controlled by the MENU are
absent, too)

omitted

If a field is present with a zero value,
default value. Use the value zero.
Brackets [

3.2

]

not

use

the

denote optional fields.

General Message Format

All DAP messages have the following form:

1 OPERATOR 1 OPERAND 1
where:
OPERATOR

This field describes the characteristics and type of
message.
It is divided into seven subfields: TYPE,
FLAGS, STREAMID, LENGTH, LEN256, BITCNT, and SYSPEC.
TYPE(1) : B

The type of DAP message.
These
numbers
are given with each DAP
message description.
Types 128-191
are reserved for DIGITAL applications
based on DAP.
Types 192-255 are
reserved for user extensions to DAP.

The DAP m e s s a g e f l a g s . B i t s i n t h i s
extensible
field
are
currently
defined a s follows:
Meaning (When S e t )

B i t (s)

Stream i d e n t i f i c a t i o n
present.

field

Length f i e l d p r e s e n t .
If bit 1
(length
field
is
set,
field
present)
LEN256 i s p r e s e n t and t h e
l e n g t h f i e l d is i n e f f e c t 2
bytes long. I l l e g a l i f b i t
1 n o t set.
The BITCNT f i e l d i s p r e s e n t .
Reserved ( 0 ) .
SYSPEC f i e l d p r e s e n t .
I f s e t , t h i s is a segmented
m e s s a g e and t h i s is n o t t h e
l a s t segment o f t h e message.
will
The
next
message
c o n t a i n t h e n e x t segment o f
t h e f u l l m e s s a g e . The n e x t
m e s s a g e m u s t b e o f t h e same
t y p e a s t h i s message. Refer
t o t h e SYSCAP f i e l d o f t h e
C o n f i g u r a t i o n m e s s a g e t o see
if
this
facility
is
supported.
The s t r e a m
identification
field.
T h i s f i e l d is i n c l u d e d o n l y i f b i t 0
o f t h e FLAGS f i e l d i s s e t .
This
f i e l d is used t o a l l o w a s i n g l e u s e r
t o have m u l t i p l e d a t a s t r e a m s i n u s e
f o r a s i n g l e open f i l e . A l l d a t a
s t r e a m s u s e t h e same l o g i c a l l i n k
(they
multiplex
on t h e STREAMID
number )

I f t h e STREAMID number is o m i t t e d , i t
is assumed t o b e z e r o . Not a l l f i l e
systems a r e capable of supporting
m u l t i p l e d a t a s t r e a m s from a s i n g l e
file.
D e n o t e s t h e l e n g t h o f t h e OPERAND
f i e l d (number o f 8 - b i t b y t e s ) . T h i s
f i e l d is optional.
I t is i n c l u d e d
o n l y i f b i t 1 o f t h e FLAGS f i e l d i s
s e t . Two o r more DAP m e s s a g e s may b e
blocked t o g e t h e r i n t o one S e s s i o n
Control buffer (usually f o r reasons
o f e f f i c i e n c y ) . I f DAP m e s s a g e s a r e
b l o c k e d , t h e LENGTH f i e l d m u s t b e
p r e s e n t s o t h e e n d o f o n e m e s s a g e and
s t a r t of t h e next can be found.

M e s s a g e s b e t w e e n 0 and 255 b y t e s l o n g
may b e b l o c k e d u s i n g o n l y t h e LENGTH
field.
DAP m e s s a g e s whose o p e r a n d
l e n g t h i s b e t w e e n 256 and 64K b y t e s
may b e b l o c k e d o n l y i f b o t h b i t s 1
and 2 o f FLAGS a r e s e t .
Lengths
greater
t h a n 64K b y t e s a r e s e n t
unblocked o r a s t h e l a s t p a r t o f a
blocked message.

LEN256(1) : B

C o n t a i n s t h e most s i g n i f i c a n t b y t e o f
a two b y t e OPERAND l e n g t h i f b i t 2 o f
FLAGS i s s e t .
LENGTH c o n t a i n s t h e
l e a s t s i g n i f i c a n t byte.
I f LEN256 i s
p r e s e n t , LENGTH must a l s o be p r e s e n t .

BITCNT(1) : B

T h i s f i e l d is v a l i d o n l y w i t h t h e
it
Data
message.
If
present,
c o n t a i n s a number i n t h e r a n g e 0-7
which i s t h e number o f unused b i t s i n
t h e f i n a l 8 - b i t b y t e o f t h e message.
I t i s r e q u i r e d o n l y when t r a n s m i t t i n g
d a t a which d o e s n o t c o m p l e t e l y f i l l
the f i n a l 8-bit
frame of a Data
is
useful
when
message.
This
a c c e s s i n g f i l e s whose b y t e s i z e is
n o t a m u l t i p l e of e i g h t . See Section
4.4.3.

SYSPEC(1-255)

: B

T h i s o p t i o n a l f i e l d is t h e system
I t can o n l y be used
specific field.
for
file
access
between
two
homogeneous s y s t e m s .
This f i e l d is
i n c l u d e d o n l y i f b i t 5 o f t h e FLAGS
I f it is used between
f i e l d is s e t .
hetrogeneous systems, it w i l l produce
a f a t a l e r r o r and t h e a c c e s s w i l l b e
aborted.
Between
homogeneous
s y s t e m s , t h i s f i e l d can be used f o r
passing system s p e c i f i c information
a s d e f i n e d by t h e s y s t e m . The SYSPEC
f i e l d c a n n o t be used w i t h
the
C o n f i g u r a t i o n message.
This field
must n o t
be
used
for
passing
i n f o r m a t i o n common t o more t h a n o n e
system.
NOTE
I f t h i s f i e l d is used, a l l
system
specific
functions
must be r e g i s t e r e d w i t h t h e
architecture
group
within
in
advance
of
DECne t
certification.

OPERAND

The information field for DAP messages.
on the TYPE field.

It is dependent

NOTE
Typically, one
DAP-speaking
process
sends one or more DAP messages to a
cooperating process which then responds
with one or more messages. Section 5
contains examples of message sequences.
This pattern repeats until the access is
complete.
Blocking DAP messages. DAP messages can
be blocked in one of two ways:

The first process blocks and sends
DAP messages up to the point where
it expects a response from
the
cooperating process. It then waits
for the response.

The first process blocks and sends
DAP
messages without regard for
response
from
the
cooperating
process.
The first process may be
way
ahead
of
the
cooperating
process. This means the cooperating
process must be able to receive a
buffer full of DAP messages, process
some of them, send a response and
then
continue
processing
DAP
messages from the same buffer from
where it left off before sending the
response. If the response was an
error, the unprocessed messages in
the buffer may no longer be valid
and must be discarded.
The first method of blocking is the
more commonly used.
The type of
blocking a
system
supports
is
specified
in
the
Configuration
message. Some small systems may not
support blocking at all.

Truncating DAP messages.
DAP messages
can be truncated up to the point of
leaving only the TYPE field provided the
fields truncated are not needed or can
be defaulted.
This is
particularly
useful
with the Acknowledge message
which reduces the ACK to a one byte
message.

3.3

Configuration Message

The Configuration message passes system configuration information
between the cooperating processes involved in DAP remote file access.
This message is sent immediately following link establishment.
The
accessed process may wait to receive a Configuration message from the
accessing process before it sends a Configuration message itself.
However, this is not necessary. The Configuration message should not
be sent blocked with any other DAP message. The reason for this is
that buffers of the appropriate size can be allocated for receiving
subsequent DAP messages. The Configuration message format is:
CONFIG BUFSIZ OSTYPE FILESYS VERSION SYSCAP
where :
CONFIG :

The OPERATOR field with TYPE = 1.

BUFSIZ(2) : B

The maximum buffer size (in bytes) of the sending
system for message exchange. The two cooperating
DAP speaking processes will use the Jesser of the
two buffer sizes as the maximum size. If one of
the two systems has an unlimited buffer size, it
sends a 0 and the two systems will use the
nonzero buffer size as the maximum.
If both
systems send 0, there is no limit on the length
of messages sent.
Operating system type (the sending
system).
Values in the range 1-191 are reserved for
192-255
are
reserved
for
DIGITAL
use:
user-specif ied operating systems.
Value

OS Type

0
1
2
3
4
5
6
7
8
9

Illegal
RT- 11
RSTS/E
RSX-11s
RSX-11M
RSX-11D
IAS
VAX/VMS
TOPS- 20
TOPS-10

RTS-8

11
12
13

OS-8
RSX-11M+
c o ~ O S / 1 1 (TOPS-20 front-end)

File system type (of the file system being used
by the process sending this message). Values in
the range 1-191 are reserved for DIGITAL use;
192-255 are reserved for user-specified file
systems.
System
Illegal
RMS-11
RMS-20
RMS- 3 2
FCS-11
RT-11
No file system supported
TOPS- 20
TOPS- 10
0s-8

VERSION :

A field identifying
version numbers.
follows:

the
This

protocol and software
field is subdivided as

where :
VERNUM(1) : B

DAP version number. This is the
same as the first digit of the
protocol version number.
DAP ECO (Modification) number.
This is the same as the second
digit of the protocol version
number.
Customer modification level
DAP. Set to 0 by DIGITAL.

DAP software version number in
binary.
This is the DIGITAL
release number. If the software
is completely user written, this
field should be 0.
User software version number

binary.
If the user modifies
DIGITAL software,
he
should
increment this byte to reflect
his modification number. Set to
0 by DIGITAL.

SYSCAP(EX-12) : BM

Generic system capabilities.
as follows:

These

are

defined

Meaning (When Set)
Supports file preallocation.
Supports sequential file organization.
Supports relative file organization.
Intended to support direct file
organization (reserved).
Supports single keyed indexed file
organization (reserved).
Supports sequential file transfer.
Supports random access by record number.
Supports random access by Virtual Block
Number.
Supports random access by key.
Intended to support random access by user
generated hash code (reserved).
Supports random access by Record File
Address (RFA)
Supports multi-keyed indexed file
organization.
Supports switching access mode. (See RAC
field in Section 3.6.)
Supports append to file access.
Supports command file submission and/or
execution as specified in the Access
message.
Supports data compression (reserved).
Supports multiple data streams.
Supports status return (reserved).
Supports blocking of DAP messages up to
response. (See note Section 3.2.)
Supports unrestricted blocking of DAP
messages. (See note Section 3.2.)
Supports the use of two byte operand
length in the DAP message header, i.e.,
LENGTH and LEN256.
Supports the file checksum option (See
ACCOPT field in the Access message and
also Section 5.5.2)
Supports the Key Definition Extended
Attributes message.
Supports the Allocation Extended
Attributes message.
Supports the Summary Extended Attributes
message.
Supports directory list.
Supports the Date and Time Extended
Attributes message.
Supports the File Protection Extended
Attributes message.

Meaning (When Set)
Supports the Access Control List Extended
Attributes message (reserved).
Supports spooling as specified by bit 20
of the FOP field (see Attributes and
Access Complete messages)
Supports command file submission as
specified by bit 21 of the FOP field.
Supports file deletion as specified by
bit 22 of the FOP field.
Supports the default file specification
(see Section 3.17) (reserved).
Supports sequential record access.
Supports the recovery option for file
transfer (reserved).
Supports the use of the BITCNT field in
the Data message.
Supports the warning Status message
(MACCODE = 6).
Supports the file rename operation.
Supports wildcard operations (see Section
5.2.19).
Supports the Go/No-Go option (see Section
3.5, ACCOPT field). (reserved)
Supports the Name message.
Supports segmented DAP messages (see bit
6 of FLAGS field). (reserved)

NOTE
Bits 5 and 33 differentiate between the
use of file transfer (see Sections 5.2.1
and 5.2.2)
and
record
access
on
sequential files (see Section 5.2.3 and
5.2.4) where file
transfer
reduces
overhead by eliminating the need for
Control messages.

3.4

Attributes Message

The Attributes message describes how data is being represented in a
file being accessed. It is sent as a part of the initial set up. The
Attributes message format is as follows:

NOTES
1.

Symbolic names,
where
supplied,
refer
to
the corresponding RMS
names. They are included here for
ease of reference only; they have
no meaning for DAP.
Values passed
to
the
accessed
system's file system may not be used
literally in
some
cases.
For
example if a value of 0 is passed in
the DEQ field, RMS systems ignore
the 0 and use the local default
rather than return an error as might
be expected.
The application of
defaults, as in this example, is a
function of individual file systems
and is in no way related to defaults
as specified in DAP. If a field is
present in a DAP message, no DAP
specified
default
will
be
substituted in place of the value it
contains.

Sometimes fields will be ignored if
they
are not applicable to the
particular operation or are
not
supported and their omission will
not affect the
operation.
For
example, RMS ignores MRS as input to
the OPEN operation. Also, with bit
map fields, sometimes bits will be
ignored
where
they
are
not
applicable to the operation or not
supported by that particular file
system.

where:
ATTRIB :

The OPERATOR field with TYPE = 2.

ATTMENU (EX-6) : BM

The following bit map specifies which of the
attributes fields will be present in the main
attributes message when the corresponding bit
is set.
These fields and only these fields
may appear in the message and they must be in
the order specified.

DATATY PE (EX- 2 ) : BM

Bit

Meaning (When Set)

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

DATATYPE
0RG
RFM
RAT
BLS
MRS
ALQ
BKS
FSZ
MRN
RUNSYS
DEQ
FOP
BSZ
D EV
SDC (reserved)
LRL

HBK
EBK
FFB
SBN

Thetype of data being transferred.
The
default
is
Image.
Unless a file has
attributes specifying
whether
the
file
contains ASCII or Image data, the accessed
process returns the value (ASCII or Image)
sent by the accessing process when opening a
file.

1 Bit 1

Meaning (when Set)
ASCII (see Note 1).
Image (default) (see Note 2)
EBCDIC (reserved)
Compressed format.
Executable code.
Privileged code.
Reserved
(set
0
when
sending
Attributes
message;
ignore when
receiving Attributes message).
Sensitive data -- zero on delete.
Data in file is set to zero when the
file is deleted for data security.

NOTES

This is the 7-bit ASCII code set as
defined in the 1968 ANSI Standard.
When transmitting or receiving 7-bit
ASCII in 8-bit frames, the high
order bit is ignored except when
using 7-bit compression.

Image is the mode where no code-set
is specified.
It is a format for
sending 8-bit quantities in
DAP
without
specifying
any
code
representation. The actual data may
be ASCII, binary or anything else.
The user process determines how to
use the data. See Section 4.4.3.

A t t r i b u t e s of t h e f i l e being a c c e s s e d .
a t t r i b u t e s a r e a s follows:
Value
(octal)

Meaning

0
20
40
60

FB$SEQ;
FB$REL;
FB$IDX;
FB$HSH;

Sequential ( d e f a u l t )
Relative.
Indexed.
Hashed ( r e s e r v e d ) .

Format of t h e r e c o r d s being
These f o r m a t s a r e a s f o l l o w s :
Value

These

transferred.

Meaning
Undefined record
format.
FB$FIX; Fixed-length r e c o r d s
(default).
FB$VAR;
Variable-length
records.
FB$VFC; V a r i a b l e w i t h f i x e d
c o n t r o l format.
FB$STM; ASCII Stream Format.

FB$UDF;

Information
about
individual records.
s e t 0.
Bit

the
attributes
of
The d e f a u l t i s a l l b i t s

Meaning (When S e t )
FORTRAN
FB$FTN;
Records
contain
c a r r i a g e c o n t r o l ( s e e Note 1 ) .
FB$CR; Records have an implied LF/CR
envelope.
FB$PRN; P r i n t f i l e c a r r i a g e c o n t r o l
where
pre- and p o s t - f i x c a r r i a g e
c o n t r o l information i s stored i n the
fixed
header
f i e l d of f i l e s i n
v a r i a b l e with fixed c o n t r o l (VFC)
format.
FB$BLK; Records t h a t do n o t span
b l o c k s ( s e e Note 2 ) .
Records have embedded format c o n t r o l
( s e e Note 3 ) .
Intended f o r COBOL c a r r i a g e c o n t r o l
(reserved).
FB$LSA; Line-sequenced ASCII Format.
MACY11 format ( n o t e 4 ) .

FORTRAN C a r r i a g e C o n t r o l .
For l i n e
p r i n t e r s a n d some t e r m i n a l s , t r e a t
t h e f i r s t character of each record
a s a carriage control character.
T h i s b i t , when s e t , i n f o r m s t h e
system t h a t t h e record l e n g t h should
n o t exceed t h e
physical
device
blocking s i z e .
With some s y s t e m s
1/0
devices
(for
a n d o n some
example, d i s k and magnetic t a p e )
t h i s may b e a f a c t o r i n d e t e r m i n i n g
the
actual
f o r m a t used on t h e
device.

T h i s b i t , when s e t , i n f o r m s t h e
s y s t e m t h a t r e c o r d s i n t h e f i l e may
contain format c o n t r o l c h a r a c t e r s
(LF, VT, a n d s o o n ) .

MACY11 f o r m a t i s a s t a n d a r d u s e d o n
10's
and
20's
to store files
d e s t i n e d f o r PDP-11's.
These f i l e s
u s u a l l y c o n t a i n 8 - b i t d a t a such as
o b j e c t c o d e o u t p u t by
a
cross
compiler.
P h y s i c a l b l o c k s i z e i n b y t e s on media.
The
d e f a u l t v a l u e i s 512. The a c t u a l b y t e s i z e
is a s s p e c i f i e d by f i e l d BSZ.
The l e n g t h o f e a c h f i l e r e c o r d i n number o f
bytes.
For v a r i a b l e - l e n g t h
records, t h i s
f i e l d s p e c i f i e s t h e maximum r e c o r d s i z e .
When t h e a c c e s s e d p r o c e s s r e c e i v e s t h e MRS
(maximum r e c o r d s i z e ) , i t m u s t c h e c k i t
a g a i n s t t h e l e n g t h of its b u f f e r . I f t h e
b u f f e r w i l l n o t accommodate t h i s s i z e r e c o r d ,
t h e accessed p r o c e s s s h o u l d r e t u r n an e r r o r .
A z e r o v a l u e means n o c h e c k i n g i s p e r f o r m e d
o n r e c o r d s i i e . MRS i s u s e d by t h e v a r i o u s
f i l e s y s t e m s i n a system-dependent manner.
The d e f a u l t i s 0 .
This f i e l d specifies the allocation quantity
i n blocks.
For f i l e c r e a t i o n , i t s p e c i f i e s
t h e i n i t i a l s i z e o f t h e new f i l e . The a c t u a l
s i z e o f t h e new f i l e i s r e t u r n e d i n t h i s
f i e l d . The d e f a u l t i s 0 .
NOTE
I g n o r e t h i s v a l u e on o p e n i n g e x i s t i n g
f i l e s . Use t h i s f i e l d o n l y t o r e t u r n
the f i l e size.
B u c k e t s i z e i n b l o c k s . Used f o r a c c e s s t o
r e l a t i v e ( n o t RMS-20), h a s h e d a n d i n d e x e d
f i l e s w i t h RMS. The d e f a u l t i s 0 (see Note 2
a t the top of Section 3 . 4 ) .

Size in bytes of fixed part of variable
length record with fixed control format. The
default is 0 (see Note 2 at the top of
Section 3.4).
Maximum record number for file (for relative
files only).
If set to 0 , checking is
suppressed. The default is 0.
Name of the Run-Time System
environment
required to execute the code contained in the
file. This field is useful to operating
systems that can emulate other operating
system environments. The default value is
accessed-operating-system-dependent.
File extension quantum size
in
virtual
blocks. This size is the amount of space, in
blocks, added to the file each time the file
is implicitly extended.
The default is 0
(see Note 2 at the top of Section 3.4).
The file access options a user requires.
default is all bits set to 0.
Bit

Meaning (When Set)
-

0
1
2
3
4
5
6
7

8
9

10
11
12
13
14
15
16

18
19
20

The

FB$RWO; Rewind on open.
FB$RWC; Rewind on close.
Reserved (0).
FB$POS; Position magnetic tape just
past the most recently
created file.
FB$DLK; Do not lock file if not
properly closed.
Reserved (0).
File Locked.
FB$CTG; A contiguous file creation
or extension required.
FB$SUP; Supersede existing file on
create.
FB$NEF; Do not position to EOF on
opening magnetic tape file
for PUT.
FB$TMP; Create temporary file.
FB$MKD; Create temporary file and
mark for delete on close.
Reserved (0).
FBSDMO; Rewind and dismount
magnetic tape on close.
FB$WCK; Enable Write checking.
FBSRCK; Enable Read checking.
FB$CIF; Create new file if one by
the same name does not
exist. If one does exist,
open the highest version
of the file.
FB$LKO; Override file lock on open
(reserved).
FB$SQO; Sequential access only.
FB$MXV; Maximize version number.
FB$SPL; Spool file to line printer
(one copy only) on close.

Bit

Meaning (When Set)
FB$SCF; Submit as command file on
close.
FBSDLT; Delete file on close. May
be used as a sub-option with
submit or spool.
FB$CBT; Contiguous best try. The
file will be created but
it will be contiguous
only when it is possible.
FB$WAT; Wait for file if it is
locked by another process
(reserved).
FB$DFW; Deferred write (REL and IDX
files) .
FB$TEF; Truncate at EOF on close
(write accessed SEQ files)
FB$OFP; Output file parse (the name
type will be preserved
until overridden).

Number of bits per "byte for data stored in
the file on the accessed node.
Data is
always transmitted in 8-bit frames
(see
Section 4.4).
When a DAP Attributes message is sent from
the accessing to the accessed system, BSZ is
required only when dealing with
systems
capable of supporting a variable byte size,
such as TOPS-20. The default value for BSZ
is
the normal default for the accessed
system's file system, for example, 8 bits per
byte for RSX.
When the Attributes message is returned from
the accessed to the accessing system, BSZ
should always be sent unless the default
applies.
The default for BSZ in a returned
Attributes message is 8 bits.
For attributes sent to the accessing node,
this
field
contains
the
generic
characteristics of the device on which a file
resides. The default is all bits set to 0.

1 Bit 1

Meaning (When Set)

FB$REC; Record oriented
FB$CCL; Carriage control device.
FB$TRM; Terminal.
FB$MDI; Directory structured.
FB$SDI; Single directory only.
FB$SQD; Sequential, block oriented (for
example, magnetic tape)
; Null device.
FB$FOD; A file-oriented device (for
example, a disk or magnetic
tape)
; Device can be shared.
FB$SPL; Device is being spooled.
FB$MNT; Device is currently mounted.
FB$DMT; Device is marked for dismount.

Meaning (When Set)

Bit
12
13
14
15

16
17
18
19
20
21

22
23
24
25

SDC(EX-6) : BM
(Reserved for
future use)

FB$ALL; Device is allocated.
FB$IDV; ~ e v i c eis capable of providing
input.
FBSODV; Device is capable of providing
output.
FBSSWL; Device is software writelocked
FB$AVL; Device is available for use.
FB$ELG; Device has error logging
enabled.
FB$MBX; Device is a mailbox.
FB$RTM; Device is realtime in nature,
not suitable for RMS use.
FB$RAD; A random access device.
; Device has read checking
enabled.
; Device has write checking
enabled.
; Device is foreign.
; Network device.
; Generic device.

Spooling device characteristics.
SDC uses
the same bit definitions as in the DEV field.
If the file is spooled, SDC contains the
characteristics of the spooling device. The
characteristics of the ultimate device are
contained in DEV.
The default is all bits
set to 0.
Longest record length.
record in the file.

Length of the longest

Highest virtual block allocated to the file.
End of file virtual block number.
First free byte in end of
size as defined in BSZ.
Starting logical block
contiguous; else 0.

3.5

file

number

block~byte

for

file

Access Message

The Access
requested.

message specifies the file name and type of
The format for the Access message is as follows:

NOTE
Symbolic names, where supplied, refer to
the corresponding RMS names. They are
included here for ease of reference
only. They have no meaning for DAP.

access

where :
ACCESS :

The OPERATOR field with TYPE = 3.

ACCFUNC (1) : B

The request code specifying the
performed is as follows:
1
2
3
4
5
6
7
8

operation

$OPEN;
Open existing file.
$CREATE; Open new file.
$RENAME; Rename a file.
$ERASE; Delete a file.
Reserved.
Directory List.
Submit as a command (batch) file.
Execute command (batch) file.

If $RENAME is specified, the FILESPEC field below
contains the old file specification and the new
file specification is contained in the
Name
message which follows the Access message.
If $CREATE is specified, but a file of that name
already exists, follow the rules of the accessed
node for file creation.
For example, the file
system may create a new file whose version number
is one greater than the current highest version
number.
NOTE
The Data Access Protocol (DAP) does not
perform
functions
beyond remote data
access. DAP should not be extended to
include RJE, spooling, or other similar
functions which, while they involve file
transfer, also require command processing,
parameter passing, and job queueing.
The
two command file submission commands are
here for historical reasons:
they were
implemented
in
the first release of
DAP-based software.
ACCOPT(EX-5) : BM

The access options are as follows:
Bit

1 Meaning (When Set)
1/0 errors are non-fatal. A record may be
skipped or repeated as specified by the
Continue Transfer message.
If not set,
1/0 errors are fatal and terminate the
access.
A status
message
will
be
returned
following each record sent to the accessed
process in
the
record
access
mode
(reserved)

Meaning (When Set)
-

status message is returned with each
record retrieved from an accessed system.
The status message should precede the Data
message so that it is always possible to
block the two into one Session Control
buffer.
When a user requires a Record
File Address (RFA) to be returned, this
option is used (reserved).

A 16 bit file checksum will be generated
by both the transmitting and receiving
nodes.
When closing
the
file,
the
accessing process sends the checksum it
generated to the accessed process in the
Access
Complete (Close) message.
The
accessed process closes the file if the
checksums agree. If they do not agree, it
returns a status message.
See Section
5.5.2.
The Go/No-Go option is to be used with
this operation.
Go/No-Go is valid only
for the Delete, Rename, and
Execute
Command
File
functions
and wildcard
operations
using
these
functions.
Go/No-Go operation causes the accessed
process to return the name of the file to
the accessing process before executing the
operation. The accessing process can then
choose whether or not to perform the
operation on the file by sending either a
Control (Resume) or
Control (Skip) See
Section 5.2.11 for state operation.
FILESPEC
(1-255) : A

The file specification in the format required by
A null file
specification
the remote node.
assumes the meaning of a null file specification
on the target node.
The file access operations a user requires:

1 Bit 1 Meaning (When Set)
FB$PUT; Put a c c e s s .
FB$GET; Get access (default).
FBSDEL; Delete access.
FB$UPD; Update access.
FB$TRN; Truncate access.
FB$BIO; Block 1/0 acess (see Note).
FB$BRO; Support switching between
block and record I/O.
NOTE
FBSREA = FB$BIO!FB$GET; Block 1/0 Read access.
FB$WRT = FB$BIO!FB$PUT; Block 1/0 Write access.

SHR(EX-3) : BM

Operations shared with other users:

Bit

Meaning (When Set)

0
1
2

4
5
6

DISPLAY (EX-4) : BM

FB$PUT; Put access.
FB$GET; Get access (default).
FB$DEL; Delete access.
FB$UPD; Update access.
FB$MSE; Enable multi-stream access.
FB$UPI; User provided interlocking
(allows multiple writers to SEQ
files)
FB$NIL; No access by other users.

Attributes and Extended Attributes messages which
are to be returned in response to this Access
message. See note 2 Section 3.6.

Bit

Meaning (When Set)
Main Attributes message (see Note
1,
Section 5.1.2).
Key definition Attributes message.
Allocation Attributes message.
Summary Attributes message.
Date and Time Attributes message.
File Protection Attributes message.
Reserved (0).
Access Control List
Attributes message (reserved).
Name message containing resultant
file specification. If the file
was opened using logical name(s) ,
this will return the file specification
of file opened without logical names.
NOTE
When opening a file and DISPLAY
requests
key
definition
and
allocation attributes for
that
file, the Attributes message must
be followed by Key Definition and
Allocation
Attributes Extension
messages specifiying for
which
keys
and
which
areas
this
information is to be returned. If
no keys or areas are specified, no
key or area information will be
returned.
See Section 5.1.2 for
the setup message sequence.

Password required to obtain access to file.

3.6

Control Message

The Control message sends c o n t r o l type information t o a
The Control message format i s a s follows:

file

system.

where:
CONTROL :

The OPERATOR f i e l d w i t h TYPE = 4 .

CTLFUNC (1) : B

S p e c i f i c c o n t r o l information:
Meaning

Value
t

$GET (01: $READ f o r block I / O ) ;
Get record
(or
block)
If
random access t o a
r e l a t i v e f i l e i s made, t h e KEY f i e l d
c o n t a i n s t h e record number. I f a random
a c c e s s t o an indexed f i l e is made, KEY
c o n t a i n s t h e key. I f s e q u e n t i a l a c c e s s is
employed, g e t the next record ( d e f a u l t ) .

If
$CONNECT;
I n i t i a t e data
stream.
m u l t i p l e d a t a streams a r e used, they a r e
multiplexed on t h e STREAMID number.
The
STREAMID number i n the Control message
i n i t i a t e s a d a t a stream. I f t h e STREAMID
number i s omitted, assume a d e f a u l t of
zero.

$UPDATE ;
Update
cur r e n t
record.
Indicates
t o t h e accessed system t h e
i n t e n t of t h e accessing system t o update
the c u r r e n t l y positioned record w i t h t h e
next d a t a transmission.

1
1

$PUT ( o r $WRITE for block I/O); I n d i c a t e s
to
the
accessed
system,
that
the
information t o follow should be w r i t t e n
i n t o the f i l e .
{DELETE;

Delete c u r r e n t record.

1 $REWIND; Rewind f i l e .

$TRUNCATE;
Truncate
file.
Writes
end-of-file
a t current position.
Used
w i t h s e q u e n t i a l f i l e s only.

Change

file

attributes

(reserved).
$RELEASE;
Unlock record s p e c i f i e d
by
Record
File
Address
in
KEY
field
(reserved).

$FREE; Unlock a l l locked records f o r t h i s
d a t a stream.
Reserved.

Meaning

Value
$FLUSH;
buffers
stream.

Write out all
and attributes

Perform
$NXTVOL ;
start-of-next-volume
(reserved)

modified
for this

1/0
data

end-of-volume
and
processing

$FIND; Find record. Same as 1,
data is not transferred.

but

the

$EXTEND; Extend this file by the amount
specified
in the following Allocation
Attributes Extension message (reserved).
$DISPLAY; Retrieve this file's attributes
as
defined
by
the
field
DISPLAY
(reserved).
SPACE FORWARD; Forward space the file by
the number of blocks specified by KEY
below. Block 1/0 only.
SPACE BACKWARD; Backward space the file
by the number of blocks specified by KEY
below. Block 1/0 only.
CTLMENU ( EX- 4) :BM

The following bits when
set,
indicate
the
following optional fields are present.
These
fields and only these fields may appear in the
message and they must be in the order specified.
Field
RAC
KEY
KRF
ROP
HSH (reserved)
DISPLAY (reserved)
If this field is not
Sets the access mode.
present, retain the option in force for the last
access. The default is 0 if not set previously.
Meaning

Value

RB$SEQ; Sequential record access.
RB$KEY; Keyed access.
RB$RFA; Access by Record File
Address
(RFA--an RMS specific access mode).
Sequential file access (the remainder of
the file is transferred sequentially from
the current file position).
Block mode;
Access by Virtual
Block
Number.
For retrieval, a Control message
must request each block as in the record
access mode.
Block mode file transfer.
Blocks are
transferred sequentially to end-of-file
without need for
a
Control
message
preceding
each block transferred.
An
is
explicit Control (Get) or
(Put)
required to start data moving.
26

F i l e o r Mode

Key

Relative F i l e s
Indexed F i l e s
Hashed F i l e s
Record F i l e Address
Access Mode
Block Mode Access

Record Number
Record Key
Record Key

Recovery

Record F i l e Address
V i r t u a l Block Number
( b i n a r y , range 1 t o n)
Input F i l e Checkpoint
Locater

Right j u s t i f y non 8-bit q u a n t i t i e s i n t h e KEY
f i e l d w i t h t h e high order and unused b i t s s e t t o
I f t h e key c o n s i s t s of
7-bit
ASCII
zero.
c h a r a c t e r s , r i g h t j u s t i f y each 7-bit c h a r a c t e r i n
an 8 - b i t frame a s i s usual f o r t h e transmission of
ASCII c h a r a c t e r s .
Key of r e f e r e n c e . I f t h i s f i e l d is not p r e s e n t ,
do not change t h e key of r e f e r e n c e . Default is
primary i f never s e t .

If this
Optional record processing f e a t u r e s .
f i e l d i s not p r e s e n t , r e t a i n the o p t i o n s i n f o r c e
f o r t h e l a s t access.

Bit

Meaning (When S e t )
P o s i t i o n t o EOF.
Fast d e l e t e ~ m a r krecord
d e l e t e d b u t do not remove
p o i n t e r s from index.
R B $ U I F ; $PUT'S update e x i s t i n g
records i n r e l a t i v e f i l e s .
RB$HSH; Use hash code i n H S H
(reserved).
RB$LOA; Follow f i l l q u a n t i t i e s .
RBSULK; Manual locking/unlocking
(reserved).
RB$TPT; Truncate P u t ~ w r i t e sEOF
a t c u r r e n t p o s i t i o n . SEQ f i l e s
only ( P u t a l s o o c c u r s ) .
RB$RAH; Read ahead.
RB$WBH; Write behind.
RB$KGE; Key i s >=.
RB$KGT; Key i s
RB$NLK; Do not lock record.
RB$RLK; Read a locked record (read
only)
RB$BIO; Block I / O .
RB$LIM; Compare f o r key l i m i t
reached ( r e s e r v e d ) .
RB$NXR; Non-existent record
processing ( r e s e r v e d ) .
RB$EOF;
RBSFDL;

HSH(1-5) : B
(Reserved f o r
f u t u r e use)

access on d i r e c t f i l e
Hash code i f keyed
employed a n d t h e user i s doing hashing.

DISPLAY(EX-4) : BM
(Reserved for
future use)

Attributes messages to be returned in response
to a request to retrieve the file's attributes
are:
Bit

1 Meaning (When Set)
Main Attributes message.
Key definition attributes.
Allocation attributes.
Summary Attributes message.
Date and Time Attributes message.
File Protection Attributes message.
Reserved (0).
Access Control List Attributes message
(reserved).
Name message containing resultant file
specification~if
file
opened
using
logical name(s), this returns the file
specification of the file opened without
logical names.
NOTE

When a file's attributes and Key
definition
and/or
allocation
attributes have been requested in
the
DISPLAY field of a Control
message, the Control message must
have been preceded by Key Definition
and/or
Allocation
Attributes
Extension messages specifying for
which
Keys
and/or
areas
this
information is to be returned. If
no keys or areas are specified, no
Key or area information will be
returned. See Section 5.2.10 for
the message sequence.
An accessing process seeing
the
accessed process does not support a
(as
particular
message
type
indicated
in
the
Configuration
message from the accessed process)
does not request that message type
in t h e DISPLAY f i e l d o f

either

the

Access Complete or Control messages.
If an unsupported message type is
requested, return an error.
FAL's written to versions of DAP
prior to 5.6 will not return a
Status
message
for
successful
completion with Get, Put, Delete,
and Find operations. FAL's written
to
DAP
version
5.6 and later
versions will
return
successful
status for these operations. See
Sections 5.2.3, 5.2.4, 5.2.17 and
5.2.18
for the operation of these
functions.

3.7

Continue Transfer Message

The Continue Transfer message tells the accessed process what action
to take when an error is detected in an 1/0 transfer. Normally, the
accessed process informs the accessing process of an 1/0 error using a
Status message.
The accessing process returns a Continue Transfer
message. This message is also used when the accessed process suspends
to await an operator decision as with Go/No-Go operation. The format
of the Continue Transfer message is:

where:
CONTRAN

CONFUNC(1) : B

The OPERATOR field with TYPE = 5.
This field specifies the recovery action to be taken:

1 value

Meaning
Try again.
Skip and continue.
Abort transfer. (Discard all records in the
pipeline until an Access Complete message is
found indicating the pipeline is clear.)
Resume processing (used to restart accessed
process processing data for this data stream
if the accessed process is suspended).

3.8

Acknowledge Message

The Acknowledge message acknowledges
access
commands,
control
connects, and the taking of a checkpoint. Its format is as follows:

ACKNOWLEDGE1
where :
ACKNOWLEDGE:

3.9

The OPERATOR field with TYPE = 6.

Access Complete Message

The Access Complete message either terminates access or acknowledges a
request to terminate access. The Access Complete message format is as
follows:
ACCOMP

CMPFUNC

FOP

CHECK

where :
ACCOMP :

The OPERATOR field with TYPE = 7.

CMPFUNC (1) : B

The a c c e s s completion f u n c t i o n s a r e :
Value

Meaning
--

Close. Terminate access. Close a f i l e
is
currently
open.
When m u l t i p l e
streams a r e i n use, c l o s e a l l of
($CLOSE)

that
data
them

Response. Sent by t h e accessed process i n
response t o a l l Access Complete messages from
t h e accessing process u n l e s s an e r r o r occurs.
Purge. Purge a f i l e .
That i s , c l o s e
d e l e t e ($CLOSE + $ERASE) t h e f i l e .

and

End-of-stream.
Terminate t h e d a t a stream
a s s o c i a t e d with t h i s STREAMID number, but do
not c l o s e t h e f i l e ($DISCONNECT)

Skip. Close t h e f i l e c u r r e n t l y a s s o c i a t e d
with
this
link
(forcefully,
if
n e c e s s a r y ~ i g n o r eany e r r o r s t h a t may occur
i n c l o s i n g t h e f i l e ) and go on t o process t h e
next f i l e . T h i s f u n c t i o n is f o r use w i t h a
s e r i e s of wildcard t r a n s f e r s .
NOTE
F A L ' s w r i t t e n t o DAP version 4 . 1
w i l l not r e t u r n an Access Complete

(Response) t o an Access Complete
(End-of-Stream)
(EOS)
FAL ' s
w r i t t e n t o l a t e r v e r s i o n s of DAP
w i l l r e t u r n an Access Complete
(Response). The Access Complete
(End-of-Stream) does not c l o s e t h e
f i l e . The accessed process should
be i n a s t a t e wherein i t can
accept another Control (Connect)
t o open another stream.

The f i l e a c c e s s o p t i o n s a user r e q u i r e s .
Refer t o
Section 3 . 4 f o r option v a l u e s . I f any p o r t i o n of the
FOP f i e l d i n t h e Access Complete i s p r e s e n t ,
the
whole FOP from t h e A t t r i b u t e s i s superseded w i t h
unspecified b i t s being s e t 0.
The 16 b i t f i l e checksum i f requested i n t h e ACCOPT
f i e l d of t h e Access message.
See Section 5 . 5 . 2 .
Send t h e checksum only i n t h e Access Complete (Close)
message.
Return a S t a t u s message i f t h e checksum i s
i n c o r r e c t . When t h i s f i e l d i s p r e s e n t , t h e accessed
If t h i s field is
process compares t h e checksums.
a b s e n t , make no checksum comparison and c l o s e the
f i l e even i f i t i s known t o c o n t a i n e r r o r s .

3.10

Data Message

The Data message transfers the file data over a DAP
message format is as follows:
DATA

RECNUM

link.

The

Data

FILEDATA

where:
DATA :

The OPERATOR field with TYPE = 8.

RECNUM(1-8) : B

This field sends the record number when accessing
relative files (or sequential files in a relative
manner, in other words, by record number).
For
random store, this field contains the record number
(for relative files) or hash code (if the user is
generating his own hash codes with hashed files).
When RECNUM is not used, the byte count is zero.
When in block mode, this field contains the VBN
instead of the record number.
For file retrieval
with recovery, this field contains the input file
checkpoint locater.

FILEDATA

The file data being
totally transparent
byte.

3.11

transferred.
This field is
and uses all 8-bits of each

Status Message

The status message returns information on the status of DAP messages
or data transfers. This message is sent synchronously in response to
another DAP message or an error during data transfer. The format is:

1 STATUS 1 STSCODE 1 RFA 1 RECNUM 1 STV 1
where:
STATUS

The OPERATOR field with TYPE = 9.

STSCODE

A 2-byte status field (16 bits) subdivided as:
15

12 11

MACCODE

MICCODE

where :

RFA(1-8) : B

MACCODE(4B):B

The macro or
functional
group
reason
for the Status message.
Table 2 specifies values for this
field.

MICCODE(12B):B

The specific type of status (by
MACCODE type). Tables 3, 4, and 5
specify values for this field.

Returns the Record File Address of the record to
which this Status message applies. If the Access
message field ACCOPT indicates a return of status
after
each record is stored, then this field
contains the record file address of the record in
the accessed system's file.

RECNUM(1-8) : B

Returns the record number for relative files when a
Status message is returned after each record is
transferred (as specified in the ACCOPT field of the
Access message).
The RECNUM field is null for
non-relative files.

STV(1-8) : B

Secondary status. Used to return secondary status
information where required. (For example, RMS uses
it for device error codes.)
Table 2
MACCODE Field Values

Value
(Octal)

Meaning

Name
-

Pending

Operation in progress.

Successful

Returns
success.

Unsupported

This implementation of DAP does not
support
the specified request.
For
example,
this
is
used
when
an
unsupported bit/field or a field/value
is encountered
which
a
particular
implementation does not support.

information

that

indicates

Reserved.
File Open

Errors that occur before
successfully opened.

Transfer
Error

Errors that occur after opening a file
and before closing that file.

Transfer
Warning

For operations on open files, indicates
the operation completed but not with
complete success.

Access
Termination

Errors
associated
access to a file.

Format

Error in parsing a message.
not correct.

Invalid

Field of message
is
invalid
(for
example, bits that are meant to be
mutually exclusive are set, an undefined
bit is set, a field value is out of
range or an illegal string is in a
field)

with

file

terminating
Format

Sync

DAP
message
synchronization.

received

Reserved.
User defined STATUS MACCODES

out

Table 3
MICCODE Field Values for Use with MACCODE
Values of 2, 10, and 11 Octal

Type of Error

Code
(Octal)

Reason
NOTE
MICCODE Format: Bits 0-5 specify the
DAP message field number.
Bits 6-11
specify the DAP message type number.

Miscellaneous

Unspecified DAP message error.
DAP message type field (TYPE) error.

Configuration
Message
errors by field

Unknown field

DAP message flags field (FLAGS)
Data
stream
identification
(STREAMID)
Length field (LENGTH).
Length extension field (LEN256)
BITCNT field (BITCNT).

field

Buffer size field (BUFSIZ)
Operating system type field (OSTYPE)
File system type field (FILESYS)
DAP version number field (VERNUM).
ECO version number field (ECONUM).
USER protocol version
number
field
(USRNUM)
DEC software
release
number
field
(SOFTVER)
User software release
number
field
(USRSOFT)
System capabilities field (SYSCAP).

. .

.
.

Attributes
Message
errors by field

Unknown field.
DAP message flags field (FLAGS).
Data
stream
identification
(STREAMID).
Length field (LENGTH)
Length extension field (LEN 256)
Bit count field (BITCNT)
System specific field (SYSPEC).

field

Attributes menu field (ATTMENU).
Data type field (DATATYPE)
File organization field (ORG).
Record format field (RFM)
Record attributes field (RAT).
Block size field (BLS1
Maximum record size field (MRS)
Allocation quantity field (ALQ).
Bucket size field (BKS)
Fixed control area size field (FSZ).
Maximum record number field (MRN)

(continued on next page)

Table 3 (Cont.)
MICCODE Field Values for Use with MACCODE
Values of 2, 10, and 11 Octal

Type of Error
Attributes
Message
errors by field
(Cont.)

Code
(Octal)

Reason

Run-time system field (RUNSYS)
Default extension quantity field (DEQ).
File options field (FOP).
Byte size field (BSZ)
Device characteristics field (DEV).
Spooling device characteristics field
(SDC); (reserved)
Longest record length field (LRL).
Highest virtual block allocated field
(HBK)
End of file block field (EBK)
First free byte field (FFB)
Starting LBN for contiguous file (SBN).

Access
Message
errors by field

Unknown field.
DAP message flags field (FLAGS).
Data
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256).
Bit count field (BITCNT).
System specific field (SYSPEC)

field

Access function field (ACCFUNC).
Access options field (ACCOPT).
File specification field (FILESPEC).
File access field (PAC)
File sharing field (SHR)
Display
attributes
request
field
(DISPLAY).
File password field (PASSWORD).

Control
Message
errors by field

Unknown field.

DAP message flags field (FLAGS)
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256)
Bit count field (BITCNT)
System specific field (SYSPEC)

Data

field

Control function field (CTLFUNC).
Control menu field (CTLMENU).
Record access field (RAC)
Key field (KEY)
Key of reference field (KRF).
Record options field (HOP)
Hash code field (HSH) ; Reserved
for
future use.
Display
attributes
request
field
(DISPLAY).

(continued on next page)

Table 3 (Cont.)
MICCODE Field Values for Use with MACCODE
Values of 2, 10, and 11 Octal

Type of Error
Continue
Message
errors by field

Code
:Octal)

Reason
Unknown field.
DAP message flags field (FLAGS).
Data
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256).
Bit count field (BITCNT)
System specific field (SYSPEC)

Continue
transfer
(CONFUNC)

function

Acknowledge
Message
errors by field

field

Unknown field.

DAP message flags field (FLAGS)
Data
stream
identification
(STREAMID)
Length field (LENGTH).
Length extension field (LEN256).
Bit count field (BITCNT)
System specific field (SYSPEC)

Access Complete
Message
errors by field

field

Unknown field.

DAP message flags field (FLAGS)
Data
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256).
Bit count field (BITCNT)
System specific field (SYSPEC)

field

Access
complete
function
(CMPFUNC)
File options field (FOP).
Checksum field (CHECK).

field

Data Message
errors by field

field

Unknown field.

DAP message flags field (FLAGS)
Data
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256)
Bit count field (BITCNT)
System specific field (SYSPEC)

field

Record number field (RECNUM)
File data field (FILEDATA)

(continued on next page)

Table 3 (Cont.)
MICCODE Field Values for Use with MACCODE
Values of 2, 10, and 11 Octal

Type of Error
Status Message
errors by field

Code
[Octal)

Reason
Unknown field.

DAP message flags field (FLAGS)
Data
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256)
Bit count field (BITCNT)
System specific field (SYSPEC).

field

Macro status code field (MACCODE).
Micro status code field (MICCODE).
Record file address field (RFA)
Record number field (RECNUM)
Secondary status field (STV).

. .

Key Definition
Message errors
by field:

Unknown field.
DAP message flags field (FLAGS).
Data
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256).
Bit count field (BITCNT)
System specific field (SYSPEC).

field

Key definition menu field (KEYMENU).
Key option flags field (FLG).
Data bucket fill quantity field (DFL).
Index bucket fill quantity field (IFL).
Key segment repeat count field (SEGCNT).
Key segment position field (POS).
Key segment size field (SIZ)
Key of reference field (REF).
Key name field (KNM)
Null key character field (NUL).

I n d e x a r e a number f i e l d

(IAN).

Lowest level area number field (LAN).
Data level area number field (DAN).
Key data type field (DTP)
Root VBN for this key field (RVB)
Hash algorithm value field (HAL).
First data bucket VBN field (DVB).
Data bucket size field (DBS).
Index bucket size field (IBS)
Level of root bucket field (LVL)
Total key size field (TKS)
Minimum record size field (MRL).

(continued on next page)

Table 3 (Cont.)
MICCODE Field Values for Use with MACCODE
Values of 2, 10, and 11 Octal

Type of Error
Allocation
message errors
by field:

Code
(Octal)

Reason
Unknown field.

DAP message flags field (FLAGS)
Data
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256)
Bit count field (BITCNT).
System specific field (SYSPEC)

field

Allocation menu field (ALLMENU).
Relative volume number field (VOL)
Alignment options field (ALN).
Allocation options field (AOP).
Starting location field (LOC)
Related file identification field (RFI)
Allocation quantity field (ALQ).
Area identification field (AID).
Bucket size field (BKZ)
Default extension quantity field (DEQ)

Summary
Message
errors by field

Unknown field.
DAP message flags field (FLAGS).
Data
stream
identification
(STREAMID).
Length field (LENGTH).
Length extension field (LEN256)
Bit count field (BITCNT)
System specific field (SYSPEC)

.
.

Summary menu field (SUMENU).
Number of keys field (NOK)
Number of areas field (NOA)
Number of record
descriptors
(NOR)
Prologue version number (PVN)

Date and Time
Message
errors by field

field

Unknown field.
DAP message flags field (FLAGS)
Data
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256).
Bit count field (BITCNT)
System specific field (SYSPEC)

field

Date and time menu field (DATMENU).
Creation date and time field (CDT).
Last update date and time field (RDT).
Deletion date and time field (EDT).
Revision number field (RVN)

(continued on next page)

Table 3 (Cont.)
MICCODE Field Values for Use with MACCODE
Values of 2, 10, and 11 Octal
-

Type of Error
Protection
Message
errors by field

Code
Octal)

field

Protection menu field (PROTMENU).
File owner field (OWNER).
System protection field (PROTSYS).
Owner protection field (PROTOWN).
Group protection field (PROTGRP).
World protection field (PROTWLD).
Name Message
errors by field

Unknown field.
DAP message flags field (FLAGS).
Data
stream
identification
( STREAMID)
Length field (LENGTH)
Length extension field (LEN256)
Bit count field (BITCNT)
System specific field (SYSPEC)

field

.
.

. .

Name type field (NAMETYPE)
Name field (NAMESPEC)
Access Control
List Message
errors by field:
(Reserved for
future use)

Unknown field.

DAP message flags field (FLAGS)
Data
stream
identification
(STREAMID)
Length field (LENGTH)
Length extension field (LEN256).
Bit count field (BITCNT).

field

System specific field (SYSPEC).

Access control list repeat count field
( ACLCNT)
Access control list entry field (ACL).

Table 4
MICCODE F i e l d Values f o r Use w i t h MACCODE
Values of 0 , 1, 4, 5 , 6 , and 7 O c t a l

Value
[Octal)
NOTE
MICCODE Format:

B i t s 0-11 c o n t a i n t h e e r r o r code
Symbolic s t a t u s c o d e s , where s u p p l i e d ,
t h e c o r r e s p o n d i n g RMS s t a t u s c o d e s .
These
c o d e s a r e i n c l u d e d h e r e f o r e a s e of
r e f e r e n c e o n l y . They have no meaning f o r DAP.

number.
refer to

1
2
3
4
5

6
7
10
11

12
13
14

15
16
17
20
21

22
23
24

25
26
27
30
31

Unspecified e r r o r .
ER$ABO; O p e r a t i o n a b o r t e d .
ER$ACC; F l l - A C P could n o t a c c e s s f i l e .
ER$ACT; FILE a c t i v i t y p r e c l u d e s o p e r a t i o n .
ER$AID; Bad a r e a I D .
ER$ALN; Alignment o p t i o n s e r r o r .
ER$ALQ; A l l o c a t i o n q u a n t i t y t o o l a r g e o r 0 v a l u e .
ER$ANI; Not ANSI D format.
ER$AOP; A l l o c a t i o n o p t i o n s e r r o r .
ER$AST; I n v a l i d ( i . e . , synch) o p e r a t i o n a t AST l e v e l .
ER$ATR; A t t r i b u t e read e r r o r .
ERSATW; A t t r i b u t e w r i t e e r r o r .
ER$BKS; Bucket s i z e t o o l a r g e .
ER$BKZ; Bucket s i z e t o o l a r g e .
ER$BLN; BLN l e n g t h e r r o r .
ER$BOF; Beginning of f i l e d e t e c t e d .
ER$BPA; P r i v a t e pool a d d r e s s .
ER$BPS; P r i v a t e pool s i z e .
ER$BUG; I n t e r n a l RMS e r r o r c o n d i t i o n d e t e c t e d .
ER$CCR; Cannot c o n n e c t RAB.
ER$CHG; $UPDATE changed a key w i t h o u t having a t t r i b u t e o f
XBSCHG s e t .
ER$CHK; Bucket format check-byte f a i l u r e .
ER$CLS; RSTS/E c l o s e f u n c t i o n f a i l e d .
ER$COD; I n v a l i d o r unsupported COD f i e l d .
ER$CRE; F l l - A C P c o u l d n o t c r e a t e f i l e (STV=sys e r r c o d e ) .
ER$CUR; No c u r r e n t r e c o r d ( o p e r a t i o n n o t preceded by
GET/FIND)

32
33
34
35
36
37
40
41
42
43
44

45
46
47
50
51

ER$DAC; F l l - A C P d e a c c e s s e r r o r d u r i n g CLOSE.
ER$DAN; Data AREA number i n v a l i d .
E R $ D E L ; RFA-Accessed r e c o r d was d e l e t e d .
ER$DEV; Bad d e v i c e , o r i n a p p r o p r i a t e d e v i c e t y p e .
ER$DIR; E r r o r i n d i r e c t o r y name.
ER$DME; Dynamic memory e x h a u s t e d .
ER$DNF; D i r e c t o r y n o t found.
ER$DNR; Device n o t r e a d y .
ER$DPE; Device.has p o s i t i o n i n g e r r o r .
ERSDTP; DTP f i e l d i n v a l i d .
ER$DUP; D u p l i c a t e key d e t e c t e d , XB$DUP n o t s e t .
ER$ENT; RSX-F11ACP e n t e r f u n c t i o n f a i l e d .
ER$ENV; O p e r a t i o n n o t s e l e c t e d . i n ORG$ macro.
ER$EOF ; ~ n d - o f -f i l e .
ER$ESS; Expanded s t r i n g a r e a t o o s h o r t .
ER$EXP; F i l e e x p i r a t i o n d a t e n o t y e t reached.
( c o n t i n u e d on n e x t page)

Table 4 (Cont.)
MICCODE Field Values for Use with MACCODE
Values of 0, 1, 4 , 5, 6 , and 7 Octal
Value
Octal)
52
53
54
55
56
57
60
61
62
63
64
65
66
67
70
71
72
73
74
75
76
77

100
101
102
103
104
105
106
107
110
Ill
112
113
114
115
116
117
120
121
122
123
124
125
126
127
130

ER$EXT; File extend failure.
ER$FAB; Not a valid FAB (BID NOT = FB$BID).
ER$FAC; Illegal FAC for REC-OP,0, or FB$PUT not set for
CREATE.
ER$FEX; File already exists.
ER$FID; Invalid file I.D.
ER$FLG; Invalid flag-bits combination.
ER$FLK; File is locked by other user.
ER$FND; RSX-F11ACP FIND function failed.
ER$FNF; File not found.
ER$FNM; Error in file name.
ER$FOP; Invalid file options.
ER$FUL; DEVICE/FILE full
ER$IAN; Index AREA number invalid.
ER$IFI; Invalid IF1 value or unopened file.
ER$IMX; Maximum NUM(254) areas/key XABS exceeded.
ER$INI; $INIT macro never issued.
ER$IOP; Operation
illegal
or
invalid
for
file
organization.
ER$IRC; Illegal record encountered (with sequential files
only).
ER$ISI; Invalid IS1 value, on unconnected RAB.
ER$KBF; Bad KEY buffer address (KBF=0).
ER$KEY; Invalid KEY field (KEY=0/neg).
ER$KRF; Invalid key-of-reference ($GET/$FIND).
ER$KSZ; KEY size too large.
ER$LAN; Lowest-level-index AREA number invalid.
ER$LBL; Not ANSI labeled tape.
ER$LBY; Logical channel busy.
ER$LCH; Logical channel number too large.
ER$LEX; Logical extend error, prior extend still valid.
ERSLOC; LOC field invalid.
ER$MAP; Buffer mapping error.
ER$MKD; Fll-ACP could not mark file for deletion.
ER$MRN; MRN value=neg or relative key>MRN.
ER$MRS; MRS value=0 for fixed length records. Also 0 for
relative files.
ER$NAM; NAM block address invalid
(NAM=0, or
not
accessible)
ER$NEF; Not positioned to EOF (sequential files only).
ER$NID; Cannot allocate internal index descriptor.
ER$NPK; Indexed file; no primary key defined.
ER$OPN; RSTS/E open function failed.
ERSORD; XAB'S not in correct order.
ER$ORG; Invalid file organization value.
ER$PLG; Error in file's prologue (reconstruct file).
ER$POS; POS field invalid (POS>MRS,STV=XAB indicator).
ER$PRM; Bad file date field retrieved.
ER$PRV; Privilege violation (0s denies access).
ER$RAB; Not a valid RAB (BID NOT=RB$BID).
ER$RAC; Illegal RAC value.
ER$RAT; Illegal record attributes.

(continued on next page)

Table 4
(Cont.)
MICCODE F i e l d V a l u e s f o r Use w i t h MACCODE
V a l u e s of 0 , 1, 4 , 5 , 6 , and 7 O c t a l

Value
(Octal)
131
1 32
133
134
135
136
137
140
141
142
143
144
1 45
146
147
150
151
152
153
154
155
156
157
160
161
162
163
164
165
166
167
170

171
172
173
174
175
176
177
200
201
202
203
204
205
206
207
210

ER$RBF; I n v a l i d r e c o r d b u f f e r a d d r e s s (ODD, o r
not
word-aligned i f BLK-10)
ER$RER; P i l e r e a d e r r o r .
ER$REX; Record a l r e a d y e x i s t s .
ER$RFA; Bad RFA v a l u e (RFA=0)
ER$RFM; I n v a l i d r e c o r d f o r m a t .
ER$RLK; T a r g e t b u c k e t l o c k e d by a n o t h e r Stream.
ERSRMV; RSX-F11 ACP remove f u n c t i o n f a i l e d .
ER$RNF; Record n o t found.
ER$RNL; Record n o t l o c k e d .
ER$ROP; I n v a l i d r e c o r d o p t i o n s .
ER$RPL; E r r o r w h i l e r e a d i n g p r o l o g u e .
ER$RRV; I n v a l i d RRV r e c o r d e n c o u n t e r e d .
ER$RSA; RAB s t r e a m c u r r e n t l y a c t i v e .
ER$RSZ; Bad r e c o r d s i z e (RSZ>MRS, o r NOT=MRS i f f i x e d
length records).
ERSRTB; Record t o o b i g f o r u s e r ' s b u f f e r .
ER$SEQ; Primary key o u t of s e q u e n c e (RAC=RB$SEQ f o r
$PUT).
ER$SHR; SHR f i e l d i n v a l i d f o r
file
(cannot
share
sequential f i l e s )
ER$SIZ; SIZ f i e l d i n v a l i d .
ER$STK; S t a c k t o o b i g f o r s a v e a r e a .
ER$SYS; System d i r e c t i v e e r r o r .
ERSTRE; Index t r e e e r r o r .
ER$TYP; E r r o r i n f i l e t y p e e x t e n s i o n on FNS t o o b i g .
ER$UBF; I n v a l i d u s e r b u f f e r a d d r ( 0 , ODD, o r i f BLK-I0
n o t word a l i g n e d )
ER$USZ; I n v a l i d u s e r b u f f e r s i z e (USZ=0).
ER$VER; E r r o r i n v e r s i o n number.
ER$VOL; I n v a l i d volume number.
ERSWER; F i l e w r i t e e r r o r (STV=sys e r r c o d e ) .
ER$WLK; Device i s w r i t e l o c k e d .
ER$WPL; E r r o r w h i l e w r i t i n g p r o l o g u e .
ERSXAB; Not a v a l i d XAB (@XAB=ODD,STV=XABi n d i c a t o r ) .
BUGDDI; D e f a u l t d i r e c t o r y i n v a l i d .
CAA
; Cannot a c c e s s argument l i s t .
CCF
; Cannot c l o s e f i l e .
CDA
; Cannot d e l i v e r AST.
CHN
; Channel a s s i g n m e n t f a i l u r e (STV=sys e r r c o d e ) .
CNTRLO; Terminal o u t p u t i g n o r e d d u e t o (CNTRL) 0.
CNTRLY; T e r m i n a l i n p u t a b o r t e d d u e t o (CNTRL) Y .
DNA
; Default filename s t r i n g address e r r o r .
DVI
; Invalid device I.D.
field.
; Expanded s t r i n g a d d r e s s e r r o r .
ESA
; Filename s t r i n g a d d r e s s e r r o r .
FNA
; FSZ f i e l d i n v a l i d .
FSZ
; I n v a l i d argument l i s t .
IAL
KFF
; Known f i l e found.
; L o g i c a l name e r r o r .
LNE
NOD
; Node name e r r o r .
NORMAL; O p e r a t i o n s u c c e s s f u l .
OKDUP; Record i n s e r t e d had d u p l i c a t e key.

( c o n t i n u e d on n e x t p a g e )

Table 4

(Cont.)

MICCODE F i e l d Values f o r Use w i t h MACCODE
Values o f 0 , 1, 4 , 5 , 6 and 7 O c t a l

Value
(Octal)
211
212
213
214
215
216
217
220
221

222
223
224
225
226
227
230
231
232
233
234
235
236
237
240
241
242
243
244
245
246
247
250

251
252
2 53

254
255
256
257
260
261
262
26 3
264
265
266
267
270
27 1
272
273

OK I D X ; Index update e r r o r o c c u r r e d - r e c o r d i n s e r t e d .
O K R L K ; Record locked b u t r e a d anyway.
O K-R R V ; Record i n s e r t e d i n primary 0.k.; may n o t
a c c e s s i b l e by secondary keys o r RPA.
CREATE; F i l e was c r e a t e d , b u t n o t opened.
PBF
; Bad prompt b u f f e r a d d r e s s .
PNDING; Async.
o p e r a t i o n pending completion.
QUO
RHB
RLF

; Quoted s t r i n g e r r o r .
; Record header b u f f e r i n v a l i d .
; Invalid related f i l e .
; Invalid resultant s t r i n g size.
; Invalid r e s u l t a n t s t r i n g address.
; Operation not s e q u e n t i a l .

RSS
RST
SQO
SUC
; Operation s u c c e s s f u l .
SPRSED; Created f i l e s u p e r s e d e d e x i s t i n g v e r s i o n .
SYN
; Filename s y n t a x e r r o r .
TMO
; Time-out p e r i o d e x p i r e d .
ER$BLK; FB$BLK r e c o r d a t t r i b u t e n o t s u p p o r t e d .
ER$BSZ; Bad b y t e s i z e .
ER$CDR; Cannot d i s c o n n e c t RAB.
ER$CGJ; Cannot g e t J F N f o r f i l e .
ER$COF; Cannot open f i l e .
ERSJFN; Bad J F N v a l u e .
ER$PEF; Cannot p o s i t i o n t o e n d - o f - f i l e .
ER$TRU; Cannot t r u n c a t e f i l e .
ER$UDF; F i l e is c u r r e n t l y i n a n undefined s t a t e : a c c e s s
is denied.
ER$XCL; F i l e must be opened f o r e x c l u s i v e a c c e s s .
; Directory f u l l .
; Handler n o t i n system.
; F a t a l hardware e r r o r .
; Attempt t o w r i t e beyond EOF.
; Hardware o p t i o n n o t p r e s e n t .
; Device n o t a t t a c h e d .
; Device a l r e a d y a t t a c h e d .
; Device n o t a t t a c h a b l e .
; S h a r a b l e r e s o u r c e i n use.
; I l l e g a l overlay request.
; Block check o r CRC e r r o r .
; C a l l e r ' s nodes e x h a u s t e d .
; Index f i l e f u l l .
; F i l e header f u l l .
; Accessed f o r w r i t e .
; F i l e header checksum f a i l u r e .
; Attribute control list error.
; F i l e a l r e a d y a c c e s s e d on LUN.
; Bad t a p e f o r m a t .
; I l l e g a l o p e r a t i o n on f i l e d e s c r i p t o r b l o c k .
; Rename; 2 d i f f e r e n t d e v i c e s .
; Rename; new f i l e n a m e a l r e a d y i n u s e .
; Cannot rename o l d f i l e system.
; F i l e a l r e a d y open.
; P a r i t y e r r o r on d e v i c e .
( c o n t i n u e d on n e x t page)

Table 4 (Cont.)
MICCODE Field Values for Use with MACCODE
Values of 0, 1, 4, 5 , 6, and 7 Octal
Value
[Octal)
; End of volume detected.
; Data over-run.
; Bad block on device.
; End of tape detected.
; No buffer space for file.
; File exceeds allocated space
no blks.
; Specified task not installed.
; Unlock error.
; No file accessed on LUN.
; Send/receive failure.
; Spool or submit command file failure.
; No more files.
; DAP file transfer checksum error.
; Quota exceeded

SPL
NMF
CRC

BUGDAP; Internal network error condition detected.
CNTRLC; Terminal input aborted due to (CNTRL) C.
; Data bucket fill size > bucket size in XAB.
DFL
; Invalid expanded string length.
ESL
IBF
; Illegal bucket format.
IBK
; Bucket size of LAN NOT = IAN in XAB.
IDX
; Index not initialized.
; Illegal file attributes (corrupt file header).
IFA
; Index bucket fill size > bucket size in XAB.
IFL
KNM
; Key name buffer not readable or writeable in XAB.
; Index bucket will not hold two keys for key of
KSI
reference.
; Multi-buffer count invalid (negative value).
MBC
NET
; Network operation failed at remote node.
OK ALK; Record is already locked.
O K D E L ; Deleted record successfully accessed.
O K L I M ; Retrieved record exceeds specified key value.
OK NOP; Key XAB not filled in.
O K R N F ; Nonexistent record successfully accessed.
; Unsupported prologue version.
PLV
; Illegal key-of-reference in XAB.
REF
; Invalid resultant string length.
RSL
RVU
; Error updating rrv's, some paths to data may
be
lost.
; Data types other than string limited to one
SEG
segment in XAB.
; Reserved
SUP
; Operation not supported over network.
WBE
; Error on write behind.
WLD
; Invalid wildcard operation.
WSF
; Working set full (can not lock buffers in working
set).
; Directory listing--error in reading volume-set
name, directory name, of file name.
; Directory
listing--error
in
reading
file,
attributes.
; Directory listing--protection violation in trying
to read the volume-set, directory or file name.
(continued on next page)

Table 4 (Cont .)
MICCODE Field Values f o r Use w i t h MACCODE
Values of 0 , 1 , 4, 5, 6 , and 7 Octal
Er ror/Reason

Value
Octal)
; Directory

SNE
SPE
UP1
ACS

TNS
BES
PES
WCC
I DR
STR

FTM

l i s t i n g ~ p r o t e c t i o nv i o l a t i o n i n t r y i n g
t o read f i l e a t t r i b u t e s .
; Directory l i s t i n g ~ f i l ea t t r i b u t e s do not e x i s t .
; Directory l i s t i n g ~ u n a b l e t o
recover d i r e c t o r y
l i s t a f t e r Continue Transfer ( S k i p ) .
; Sharing not enabled.
; Sharing page count exceeded.
; UP1 b i t not s e t when sharing w i t h BRO s e t .
; Error i n access c o n t r o l s t r i n g (poor man's
route
through e r r o r )
; Terminator not seen.
; Bad escape sequence.
; P a r t i a l escape sequence.
; Invalid wildcard c o n t e x t value.
; Invalid d i r e c t o r y rename o p e r a t i o n .
; User s t r u c t u r e (FAB/RAB)
became i n v a l i d during
operation.
; Network f i l e t r a n s f e r mode precludes o p e r a t i o n .

; User

defined e r r o r s

Table 5
MICCODE Field Values
( w i t h MACCODE Value of 1 2 O c t a l )

Value
(Octal)
NOTE
MICCODE Format:
type number.

0
1
2
3
4

5
6
7
10

11
12

13
14

15
16
17

B i t s 0-11

contain

the

message

Unknown message type
Configuration message
A t t r i b u t e s message
Access message
Control message
Continue Transfer message
Acknowledge message
Access Complete message
Data message
S t a t u s message
Key D e f i n i t i o n A t t r i b u t e s Extension message
Allocation A t t r i b u t e s Extension message
Summary A t t r i b u t e s Extension message
Date and Time A t t r i b u t e s Extension message
P r o t e c t i o n A t t r i b u t e s Extension message
Name message
Access Control L i s t Extended A t t r i b u t e s message

3.12

Key D e f i n i t i o n A t t r i b u t e s E x t e n s i o n Message

Each key i s d e f i n e d by a g r o u p o f 19 f i e l d s .
d e f i n i t i o n message is:

The

form

the

key

POS SIZ [POS SIZ...]
b

KEYDEF :

The o p e r a t o r f i e l d w i t h TYPE = 1 0 .

KEYMENU(EX-6) : BM

The f o l l o w i n g b i t map s p e c i f i e s which o f t h e
f o l l o w i n g f i e l d s a r e p r e s e n t i n t h i s message.
These f i e l d s and o n l y t h e s e f i e l d s may a p p e a r i n
t h e message and t h e y must be i n t h e o r d e r
specified.
--

Bit

Meaning (When S e t )
FLG
DFL
I FL
NSG, POS and SIZ
REF
KNM
NUL
I AN
LAN
DAN
DTP
RVB
HAL ( r e s e r v e d )
DVB
DB S
IBS
LVL
TKS
MRL

Key o p t i o n f l a g
b i t 0 = XB$DUP d u p l i c a t e s a l l o w e d
b i t 1 = XB$CHG a l l o w keys t o change
b i t 2 = XB$NUL n u l l key c h a r a c t e r d e f i n e d
Data b u c k e t f i l l .
Index b u c k e t f i l l .
Number o f segments (max. 8 ) needed t o d e f i n e t h e
key i n t h e r e c o r d .
For e a c h segment, t h e r e w i l l
be a POS, SIZ p a i r .
For example, i f MSG
c o n t a i n s 3 , t h e following sequence o f f i e l d s
would a p p e a r :

P o s i t i o n o f key i n r e c o r d by b y t e number.
f i r s t b y t e i n t h e r e c o r d i s b y t e 0.
S i z e o f key i n r e c o r d i n b y t e s .
Key o f r e f e r e n c e i n d i c a t o r .

The

Key name correspoding t o key of r e f e r e n c e
above.
NUL(1)

: B

Value of n u l l key c h a r a c t e r .

IAN(1) : B

Index - a r e a number.

LAN(1) : B

Lowest l e v e l index a r e a number.

DAN(1)

: B

Data l e v e l a r e a number.

DTP(1) : B

Data type.

RVB(1-8)

Root VBN f o r key.

: B

(REP)

HAL(1-5) : B

Hash algorithm value ( r e s e r v e d ) .

DVB(I-8) : B

F i r s t d a t a bucket s t a r t v i r t u a l block number.

DBS(1) : B

Data bucket s i z e f i e l d .

IBS(1) : B

Index bucket s i z e f i e l d .

LVL(1) : B

Level of r o o t bucket.

TKS(1) : B

Total key s i z e .
Minimum record l e n g t h ;
t h e minimum
record
length i n b y t e s which w i l l t o t a l l y c o n t a i n t h e
key f i e l d f o r t h e key described by t h i s message.

3.13

Allocation A t t r i b u t e s Extension Message

Use t h e Allocation message when c r e a t i n g o r e x p l i c i t l y extending a
f i l e t o s p e c i f y t h e c h a r a c t e r of t h e a l l o c a t i o n . The form of t h e
a l l o c a t i o n message is:
ALLMENU VOL ALN AOP LOC RFI ALQ

ALLOC :

The o p e r a t o r f i e l d w i t h TYPE = 11.

ALLMENU (EX-6) : BM

The following b i t map s p e c i f i e s which of t h e
following f i e l d s a r e p r e s e n t i n t h i s message.
These f i e l d s and only t h e s e f i e l d s nay appear i n
the
message.
They must be i n t h e order
specified.
it
--

0
1
2

3
4
5

6
7

Meaning (Mm Set)

VOL
ALN
AOP
LOC
RFI
ALQ
AID
BKZ
DEQ

(reserved)

Relative volume number of a volume s e t on
t h i s a r e a or f i l e w i l l be a l l o c a t e d .

which

Alignment options

1 B i t 1 Meaning 1 Explanation

No
specified
allocation
placement.
Align on cylinder boundary.
Align
to
specified
logical
block.
Allocate a s near as possible to
specified virtual block.
Allocate a s near as possible to
specified related file.
Allocation options
Bit

Meaning

Explanation

XB$HRD

1
2

XB$CTG
XB$CBT

XB$ONC

If the requested alignment can
not be done, return an error.
Contiguous allocation required.
Contiguous best try.
The file
will be created, but it will be
contiguous only when
it
is
possible.
Allocate space on any cylinder
boundary.

Allocation starting point.

Value is as follows:

number
If ALN = XB$CYL, LOC is the cylinder
where allocation is to start.
If ALN = XB$LBN, LOC is the logical block where
allocation is to start.
If ALN = XB$VBN, LOC is the virtual block near
which allocation should start;
0 (default) means as near as
possible to current EOF.
If ALN = XB$RFI, LOC is a VBN but a VBN in the
related file.
Related file I.D.

(reserved).

The amount of space in virtual blocks to be
allocated.
Returns actual size of allocation.
For DISPLAY, r e t u r n s s i z e of a r e a .

Area I.D. The area number used to identify
area for reference by a key definition.

Bucket size for this area.
The default extension quantity
in
virtual
blocks.
Specifies the amount of space to be
added to the area whenever it is extended
automatically. It overrides the DEQ in the main
Attributes message.

3.14

Summary Attributes Extension Message

The Summary Attributes Extension message comprises
the
fields
described below. The accessed process optionally returns this message
to the accessing process on a file open, file create, display of a
file's attributes or directory list.
The format of the Summary
Attributes Extension message is:
SUMMARY SUMENU NOK NOA NOR PVN
where :
SUMMARY :

The operator field with TYPE = 12.

SUMENU(EX-6) : BM

The following bit map specifies which of the
following fields are present in this message.
These fields and only these fields may appear in
the message and they must appear in the order
specified.

1 Bit

1 Meaning (When Set) 1
NOK
NOA
NOR
PVN
-

Number of keys defined in file.
Number of areas defined in file.
Number of record descriptors in file.
Prologue version number.

3.15

Date and Time Attributes Extension Message

The Date and Time Attributes Extension message is composed of the
fields described below.
This message is optionally returned to the
accessing process by the accessed process on a file open, file create,
display of a file's attributes or directory list. The form of the
message is:

1 D A T E 1 DATMENU 1 CDT 1 RDT 1 EDT 1 RVN 1
where :
DATIME :

The operator field with TYPE = 13.

DATMENU(EX-6) : BM

The following bit map specifies which of the
following fields are present in this message.
These fields and only these fields may appear in
the message and they must appear in the order
specified.
Bit
0

1
2

Meaning (When Set)
CDT
RDT
EDT
RVN
J

Date and time file created in
Time (NST)

Network

Standard

Date and time file last updated in NST.
Date and time file may be deleted in NST.
The preceding three
following format:

fields

should

the

where:
dd is the day
mon is a three letter abbreviation for the month
as follows:
JAN
FEB
MAR
APR
MAY
J UN
JUL
AUG
SEP
OCT
NOV
DEC
yy is the year
b is blank (space)
hh is the hour
mm is the minutes
ss is the seconds
Revision n u m b e r ~ t h enumber of
has been modified.

times

the

file

Network standard time (NST) is the time standard chosen for each
network to effect synchronization of remote file access operations and
their results. For example, if a user in London creates a file in New
York with a deletion time of 2 a.m., does he mean 2 a.m.
in London or
New York? NST resolves this problem. NST may be local time (for
example, for networks wholly contained in one time zone), GUT or some
other agreed on time.

3.16

Protection Attributes Extension Message

Use the Protection Attributes Extension message when creating a file
to specify the protection for that file. If this information is not
present when creating a new file, the file will be created with the
default protection of the accessed node. This message may also be
used to return a file's protection code to the accessing process on a
file open, display of the file's attributes or directory list. The
format of the Protection Attributes Extension message is:
PROTECT PROTMENU OWNER PROTSYS

where:
PROTECT :

The OPERATOR field with TYPE = 14.

PROTMENU(EX-6) : BM

The following bit map specifies which of the
following fields are present in this message.
If the field is not present, the default, if
any, should be used.
These fields and only
these fields may appear in the message and they
must appear in the order specified.
Bit

Meaning (When Set)
OWNER
PROTSYS
PROTOWN
PROTGRD
PROTWLD

The name or user code (for example, UIC such as
240,220) of the file owner. When creating a
file and when the file system allows the owner
to be user-specified, this field, if present,
specifies the owner of the file. If this field
is not present, the file owner information is
taken from the user identification information
which comes with the connect. Alternatively, if
the User Identification message is being used
(see Appendix A) owner information may be taken
from it.
File protection for system access rights.
Bit

Meaning (When Set)
Deny read access.
Deny write access.
Deny execute access.
Deny delete access.
Deny append access.
Deny directory list access.
Deny update access.
Deny
change
access
protection
attribute.
Deny extend access.

PROTOWN (EX-3) : BM

File protection for file owner access rights.
Refer to the bit map used for PROTSYS above.

PROTGRP (EX-3) : BM

File protection for group access rights.
to the bit map used for PROTSYS above.

PROTWLD(EX-3) : BM

File protection for general (world) access.
Refer to the bit map used for PROTSYS above.

Refer

3.17

Name Message

Use the Name message when renaming 'a file to contain the new name the
file will have after the operation is complete. Use the Name message
with the directory listing to return the name of each file for which
attributes are returned. It may also be used when opening or creating
a file to contain the default or related file specification. The form
of the name message is:
NAME NAMETYPE NAMESPEC
where:
NAME :

The operator field with TYPE = 15.

NAMETYPE(EX-3) : BM

Type of name contained in NAMESPEC field.
Meaning
File specification
File name
Directory name
Volume or structure name
Default file specification
(reserved)
Related file specification
(reserved)
NOTE
Here the file specification means the
full file specification including the
volume, directory, and file name.

NAMESPEC(1-200) : A

The file specification in the
remote
node.
This
ASCII
interpreted by DAP software.

format
field

3.18 Access Control List Attributes Extension Message
Future Use)

of
is

the
not

(Reserved for

The Access Control List (ACL) message specifies a list of users and
the access rights they have to this file. Each ACL entry is in the
format of the system where the file resides. The list is potentially
very long and therefore this message has a facility for specifying if
this is the last of a sequence of ACL messages. The form of the ACL
message is:
ACLTYPE ACLCNT ACL [ACL. . . I
ACLTYPE :

The operator field with TYPE = 16.

ACLCNT(1) : B

The absolute value of this field is the number
of repetitions of the ACL field in this message.
If this field contains a negative value, this is
the last in a sequence of ACL messages.

ACL(1-80)

Access control list entry. There is one entry
for each user having access to the file. This
field is treated as a literal string (not parsed
by accessing system) and is in the format of the
accessed system.

: A

4.0

FILE ORGANIZATION

4.1

Types of Files

The following types of files are addressed by this specification:
Sequential. Each record's position depends on the position of
the previous record.
Relative. Each record in the file has a unique identifying
number, its record number. Records may be accessed randomly
by specifying their record number in a Control message.
Hashed/Indexed.
These files have records organized according
to some classification method, usually an access key. Within
a particular key for indexed files, the records are assumed to
be logically sequential.

4.2

Record Formats and Attributes

There are two ways in which ASCII records are stored in
systems:

DIGITAL

file

Byte Count. A byte count associated with the record
file indicates how long the record is and is
determine record boundaries.

Stream. The ASCII record is stored exactly as is.
The
record is assumed to be terminated with one of the following
delimiters:
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.

(FF)
(OLE)
(DC1)
(DC2)

in the
used to

-- Form feed
-- Data link escape

(DC3)

(DC4)
(VT)
(LF)
(ESC)
(*Z)

-- Vertical tab
-- Line feed
-- Escape
-- Control Z

Files using ASCII stream often do not have record attributes
stored with the file.
DAP supports four ASCII record formats:
1.

Fixed length records

Variable length records

Variable with fixed control

ASCII stream

In addition, DAP supports the following eight attributes:
FORTRAN car r iage control
COBOL carriage control
Print file carriage control
Implied LF/CR envelope for printing
Embedded carriage control
Line sequential ASCII
MACY 11
None of the above

Handling Stream ASCII
Stream ASCII files consist of a string
4.2.1
of ASCII characters with no explicit record structure imposed upon the
data within the file. Records in a stream ASCII file are defined by a
set of delimiters (see Section 4.2) where each record is terminated by
one of the delimiters. DAP processes transferring stream ASCII data
records perform no transformations upon the records. All characters
in the records, up to and including the delimiter, are sent as a
single record in a DAP Data message. No characters, including NULLS,
are stripped or replaced.
Stream ASCII files may have
other
attributes as well as stream ASCII, for example, FORTRAN carriage
control.

DAP does not specify data or format conversions
4.2.2
Conversions
that may be necessary when sending data from one type of system to
another. It is the responsibility of the user process (accessing
process) to make any necessary conversions when transferring data
between unlike
systems.
The
accessed
process
(server)
is
non-intelligent and does only what it is told. The accessed process
executes a protocol function only if it supports that type of
operation or attribute.
If an accessed process does not support an
operation or attribute, it returns an appropriate Status message.
Thus, if a conversion must be made, for example, sending a Stream
ASCII file to a remote system supporting variable length byte count
records but not Stream ASCII, the accessing process (user) must
perform the conversion before sending each record of the file.

NOTE
While this is not a part of the DAP
specification, the following algorithm
has been used effectively in several
DAP-speaking user processes to determine
what (if any) conversions must be made
when trying to store a file on a remote
file system:
1.

Open file using file's attributes on
local system.

If no error on Attributes message,
send file and terminate, else go to
step 3 .

Send new Attributes
and
Access
Complete messages using the next
most
likely
attributes
to
be
supported by the remote system.

If no error on Attributes message,
send file and terminate, else go to
step 3 .
This should almost never require
more than two repetitions of step 3
as most ASCII files are
either
stream
or variable with implied
CR/LF.

4.3

Data Formats

4.3.1 Fixed-Length Records - All records are of the fixed length
specified in the MRS field. They are delimited by physical message
blocks (that is, the last byte in a Data message is the end of the
record).

Variable-Length
Records - These
records
are
like
the
fixed-length records except the record length is variable with the
maximum length being specified in the MRS field.
4.3.2

4 . 3 . 3 Variable with Fixed-Control Format Records - These records are
normal variable-length records with an associated fixed-length field
used for control purposes. In DAP Data messages, this fixed-length
control field immediately precedes and is contiguous with the variable
part of the record. The length of the fixed field is found in the FSZ
field in the Attributes message. MRS contains the maximum length of
the variable portion only. FSZ + MRS = total maximum record length.
Regardless of the type of the data in the variable portion of the
record, the data in the fixed portion is always sent as a binary field
contained in an integral number of 8-bit bytes.

4.3.4
ASCII S t r e a m
Here a f i l e c o n t a i n s j u s t a s t r e a m o f ASCII
However, d e l i m i t e r s are
c h a r a c t e r s w i t h no r e a l c o n c e p t o f r e c o r d s .
used t o t e r m i n a t e " r e c o r d s " f o r p u r p o s e s o f r e a d i n g and w r i t i n g t h e
file.

4.4

S u p p o r t e d Data Types

The DATATYPE f i e l d o f t h e A t t r i b u t e s message
r e p r e s e n t a t i o n used t o t r a n s f e r d a t a . These are:

defines

the

code

ASCII
Image
EBCDIC (Reserved)

I n a d d i t i o n , t h e r e i s a COMPRESSION o p t i o n mode, which c a n be used
w i t h a n y o f t h e above. T h i s compressed mode r e d u c e s t h e amount o f
d a t a s e n t by e n c o d i n g b l a n k s and d u p l i c a t e s .

T h i s i s t h e 7 - b i t ASCII c o d e - s e t a s d e f i n e d i n t h e 1968
4.4.1
ASCII
ANSI s t a n d a r d .
To t r a n s m i t t h i s w i t h i n 8 - b i t f r a m e s , t h e h i g h o r d e r
b i t i s i g n o r e d e x c e p t when u s i n g 7 - b i t c o m p r e s s i o n . On c a r d r e a d e r s ,
t h i s r e f e r s t o t h e ASCII e n c o d i n g o f t h e punches i n t o t h e 128
c h a r a c t e r codes.

4.4.2

- t h i s i s a n IBM 8 - b i t EBCDIC c o d e set.

EBCDIC

(Reserved)

T h i s i s a mode f o r t r a n s m i t t i n g d a t a i n DAP where no
4.4.3
Image
code s e t i s s p e c i f i e d and d a t a r e c o r d s ( o r b l o c k s ) a r e s i m p l y r e g a r d e d
a s o r d e r e d s t r i n g s of b i t s .
The number o f b i t s i n a b i t s t r i n g (image
mode r e c o r d ) need n o t be a m u l t i p l e o f 8 a l t h o u g h t h e b i t s t r i n g s a r e
i n f a c t t r a n s m i t t e d i n 8 - b i t f r a m e s ( a r e q u i r e m e n t o f lower l e v e l
protocols)

When t r a n s m i t t i n g Image d a t a , i f t h e number o f d a t a b i t s i n t h e
message i s n o t a m u l t i p l e of 8 ( t h e number o f a c t u a l d a t a b i t s i n a
DAP Data message m u s t be a m u l t i p l e o f t h e b y t e s i z e a s s p e c i f i e d by
BSZ i n t h e A t t r i b u t e s m e s s a g e ) , t h e f i e l d BITCNT i n t h e h e a d e r of t h e
Data message must be u s e d . The BITCNT f i e l d s p e c i f i e s t h e number of
b i t s i n t h e f i n a l â‚¬!-b frame o f t h e Data message which a r e n o t a c t u a l
data bits.
The non-data b i t s a r e padding b i t s r e q u i r e d t o f i l l o u t
t h e 8 - b i t frame.
When t r a n s f e r r i n g b i t s t r i n g s where t h e b i t c o u n t i s a m u l t i p l e o f
i t i s n o t n e c e s s a r y t o u s e BITCNT.

The o r d e r i n t h e b i t s t r i n g s i s low o r d e r b i t o f low o r d e r b y t e f i r s t .
second b i t of low b y t e . and s o o n , f o l l o w e d by t h e same s e q u e n c e f o r
successively higher order bytes.
For example, c o n s i d e r r e t r i e v i n g t h e
3 b y t e r e c o r d w i t h 6 - b i t b y t e s shown below. The o r d e r o f t h e s t r i n g
i s a s shown below w i t h t h e f i r s t b i t on t h e r i g h t and t h e l a s t b i t i n
t h e s t r i n g on t h e l e f t ( t h e t o p row o f s i n g l e d i g i t numbers i n s i d e t h e
boxes i s b y t e numbers and t h e bottom row i s b i t numbers. Thus f o r any
b i t p o s i t i o n i n t h e s t r i n g , t h e t o p d i g i t g i v e s t h e b y t e and t h e
bottom d i g i t t h e b i t w i t h i n t h a t b y t e ) .

byte 2

byte 1

byte 0

I n Image r e c o r d mode, t h i s s t r i n g t r a n s m i t s i n 3 8 - b i t f r a m e s i n a DAP
Data message a s f o l l o w s :
frame 2

frame 1

frame 0

x x x x x x 2 2
5 4

2 2 2 2 1 1 1 1
3 2 1 0 5 4 3 2

1 1 0 0 0 0 0 0
1 0 5 4 3 2 1 9

w i t h frame 0 b e i n g t r a n s m i t t e d f i r s t . low o r d e r b i t f i r s t .
a r e padding. BITCNT is 6 f o r t h i s DAP Data message.

The

x's

I f t h i s image r e c o r d i s b e i n g s e n t t o a s y s t e m which
7-bit b y t e s , t h i s record is s t o r e d a s follows:

data

byte 2

byte 1

byte 0

x x x 2 2 2 2
5 4 3 2

2 2 1 1 1 1 1
1 0 5 4 3 2 1

1 0 0 0 0 0 0
0 5 4 3 2 1 0

stores

4.4.4
Compression
Any o f t h e e n c o d i n g s , even t h e Image mode. may b e
compressed on t r a n s m i s s i o n t o e l i m i n a t e t h e s e n d i n g o f d u p l i c a t e s and
m u l t i p l e b l a n k s . The c o m p r e s s i o n t e c h n i q u e is s l i g h t l y d i f f e r e n t w i t h
7 - b i t and 8 - b i t c h a r a c t e r e n c o d i n g s .
7-bi t compression.:

Send non-compressed c h a r a c t e r s w i t h h i g h o r d e r b i t
(0) (7-bit char).
low 7 - b i t s = c h a r a c t e r :

Send b l a n k s a s h i g h b i t s = 1 0 f o l l o w e d by number o f b l a n k s i n
6-bit binary:
( 1 0 ) (number b l a n k s )

Send r e p e t i t i o n s a s h i g h b i t s = 110 f o l l o w e d by number o f
r e p e t i t i o n s i n 5-bit binary:
( 1 1 0 ) (number r e p s ) f o l l o w e d by
t h e repeated character.

An e s c a p e scheme a l l o w s s e n d i n g o f 1 2 - b i t c a r d images when
t h e y d o n o t e n c o d e i n t o t h e ASCII code set by s e n d i n g h i g h
b i t s = 1111 f o l l o w e d by columns 12-1 and a n o t h e r c h a r a c t e r o f
columns 2-9.
For example, s e n d (1111) (12.11.0.1) i n t h e
f i r s t c h a r a c t e r and
(2.3,4.5.6.7.8,9)
in
the
second
character.

and

The high bit sequence
expansion.

1110

has

been

reserved

for

future

In the case of repetitions the repeated character
12-bit image which is sent as 2-characters.

may

Summary 7-bit compression:
~ X X X X X X X 7-bit non-compressed characters
~ ~ X X X X X X number of blanks (the character octal

40)

110xxxxx
number of repeated characters
llllxxxx
12-bit card image
xxxxxxxx
12-bit card image (continued)
1 1 1 0 ~ reserved
~ ~ ~
8-bit compression:
With &bit codes the blanks, repetitions and 12-bit card image are the
same as the 7-bit case. Precede 8-bit non-compressed strings by a
count of the string length with high bit = 0 followed by 7-bit count:
(0) (count). This is followed by "count" 8-bit characters. Following
this may be another string, blanks or repetitions.
Summary:
~ X X X X X X X number
~ ~ X X X X X X number

110xxxxx
1 1 1 0
llllxxxx
xxxxxxxx

of non-compressed characters
of nulls (all zero bytes)
number of repetitions
~ reserved
~ ~ ~
12-bit card image
12-bit card image (continued)

The receiver of compressed data must be able to expand it according to
the rules just given.
Do not use data compression unless the
Configuration messages from both systems indicate they both support
file compression (bit 15). The compressed format bit of the DATATYPE
field in the Attributes message indicates the use of file compression.

5.0

OPERATION

DAP transfers data to and from 1/0 devices and mass storage files
independent of the 1/0 structure of the system being accessed. This
transfer is accomplished by communication with a DAP process that
accepts DAP requests on the network side and translates them into
equivalent requests to the local 1/0 system.
From the network it
appears as if DECnet systems support DAP messages directly within
their file systems.
DAP provides the mechanism for setting up the conversation path for
remote file access, transferring data over the link, and terminating
the logical link.

5.1

Setting up the Link

Processes that implement the DAP protocol operate at the application
level within a DECnet system. They use the lower level interprocess
communication facilities of the network for the creation and flow
control of the data path (logical link) between the processes
exchanging messages within the DAP environment.
Once the link is
established, the processes may exchange DAP messages over the link.
Each remote file access in progress uses a separate logical link.
This means a single user cannot access more than one file at a time
over a single logical link. It also means that several users cannot
access the same file over a single logical link. However, a single
logical link can be used to access more than one file provided access
to the files is sequential and does not overlap.
A lower level interprocess communication protocol passes access
control
information (user identification, password, and account
identification) from the accessing (user) DAP process to the accessed
(server) DAP process.
Following link establishment, the DAP-speaking processes
Configuration messages. The purposes of this exchange are:
size

for

exchange

To establish the maximum buffer
level protocol messages

exchanging

To identify system type to each other

To enable one DAP process to know which
protocol the other DAP process speaks

To inform the opposite process of the generic capabilities of
the system sending the message

version

lower

the

The system type is used when it is necessary to know the type of both
the operating system and the file system on the other end of the link.
This is helpful, for example, in deciding if block mode file transfer
can be used when transferring files between like systems or if
multiple data streams can be initiated as is possible between
RMS-based systems.
The capabilities field of the Configuration message indicates to each
of the DAP processes the generic capabilities of the other DAP process
with which it is communicating. This field determines the type of
file support offered by a remote system without resorting to trial and
error techniques.

The node where t h e f i l e o r d e v i c e r e s i d e s i s t h e a c c e s s e d node w h i l e
t h e node where t h e u s e r p r o c e s s i s l o c a t e d is t h e a c c e s s i n g node. The
a c c e s s i n g p r o c e s s i n i t i a t e s t h e c o n n e c t i o n . For e a c h DAP message s e n t
o v e r t h e l i n k , a t r a n s m i t r e q u e s t and c o r r e s p o n d i n g r e c e i v e r e q u e s t
must be i s s u e d t o S e s s i o n C o n t r o l ( D N A S e s s i o n C o n t r o l F u n c t i o n a l
Specification).
T h i s document e x p l a i n s t h e DAP messages o n l y and
assumes t h a t t h e n e c e s s a r y r e c e i v e s and t r a n s m i t s a r e i s s u e d by t h e
processes involved.
A f t e r l i n k c r e a t i o n and t h e exchange of C o n f i g u r a t i o n m e s s a g e s , t h e
a c c e s s i n g p r o c e s s s e n d s a n A t t r i b u t e s message, o p t i o n a l l y f o l l o w e d by
one o r more Extended A t t r i b u t e s m e s s a g e s , s p e c i f y i n g t h e mode and
f o r m a t of t h e d a t a and t h e s t r u c t u r e o f t h e f i l e . T h i s i s t h e n
f o l l o w e d by a n Access message s p e c i f y i n g t h e d e s i r e d o p e r a t i o n .
The
Access message may be p r e c e d e d by a Name message i f t h e d e f a u l t
filename o p t i o n i s required.
The A t t r i b u t e s , Extended A t t r i b u t e s ,
Name, and Access messages may be b l o c k e d and s e n t t o g e t h e r i n o n e
t r a n s m i s s i o n i f b u f f e r s p a c e is a v a i l a b l e ( t h e LENGTH f i e l d must be
u s e d ) and i f b l o c k i n g i s s u p p o r t e d a s i n d i c a t e d by t h e C o n f i g u r a t i o n
message. A l t e r n a t e l y , i f a DAP message i s t o o l o n g t o b e s e n t a s a
single
entity
due t o l i m i t a t i o n s o f t h e u n d e r l y i n g T r a n s p o r t
mechanism, t h e DAP message may be segmented and s e n t i n two o r more
p i e c e s ( s e e FLAGS f i e l d i n message h e a d e r ) i f s e g m e n t a t i o n is
supported

Systems n o t r e t a i n i n g t h e f i l e a t t r i b u t e s u s e t h e A t t r i b u t e s message
t o s e t t h e a t t r i b u t e s f o r t h e t r a n s f e r . When c r e a t i n g a new f i l e , t h e
A t t r i b u t e s message s e n t by t h e a c c e s s i n g p r o c e s s s p e c i f i e s t h e
a t t r i b u t e s t h e new f i l e s h o u l d have.
I f t h e accessed system d o e s n o t
s u p p o r t t h e s e a t t r i b u t e s , i t r e t u r n s a S t a t u s message t o t h a t e f f e c t .
When s t o r i n g r e c o r d s w i t h s y s t e m s r e t a i n i n g a t t r i b u t e s , t h e a c c e s s i n g
s y s t e m u s e s t h e A t t r i b u t e s message r e t u r n e d by t h e a c c e s s e d s y s t e m t o
i n d i c a t e t h e a t t r i b u t e s t h e r e c o r d s b e i n g s e n t s h o u l d h a v e . For
record r e t r i e v a l with systems r e t a i n i n g a t t r i b u t e s , r e c o r d s a r e
t r a n s f e r r e d w i t h t h e a t t r i b u t e s of t h e A t t r i b u t e s messages r e t u r n e d by
the accessed process.
A f t e r t h e i n i t i a l s e t up messages a r e s e n t , t h e a c c e s s i n g s y s t e m
r e c e i v e s a r e s p o n s e from t h e a c c e s s e d p r o c e s s .
If the access
s p e c i f i e d o p e n s a f i l e , a n A t t r i b u t e s message and Extended A t t r i b u t e s
messages f o l l o w e d by an Acknowledge message i s s e n t from t h e a c c e s s e d
system c o n t a i n i n g t h e a c t u a l a t t r i b u t e s of t h e accessed f i l e .
If the
o p e r a t i o n s p e c i f i e d i n t h e Access message d e l e t e s , renames o r e x e c u t e s
a f i l e , no A t t r i b u t e s messages o r Acknowledge messages a r e r e t u r n e d
and t h e r e s p o n s e i s an Access Complete message.
To minimize t h e t y i n g up o f network r e s o u r c e s ( s u c h a s l o g i c a l l i n k s
and b u f f e r s ) , t h e C o n f i g u r a t i o n , A t t r i b u t e s , Extended A t t r i b u t e s ,
Name, and Access messages s h o u l d be s e n t i n a t i m e l y manner. A t i m e r
may be s e t f o r e a c h message and i f i t d o e s n o t a r r i v e i n a r e a s o n a b l e
t i m e t h e l i n k may be d i s c o n n e c t e d by t h e a c c e s s e d p r o c e s s . A f t e r t h e
Acknowledge message h a s been r e c e i v e d , t h e f i l e i s open and t h e
a c c e s s i n g p r o c e s s s e t s t h e p a c e f o r a c c e s s of t h e f i l e .
I f t h e r e a r e e r r o r s i n t h e s e t u p p r o c e d u r e , a S t a t u s message
returned.
NOTE
A r e c e i v e must a l w a y s be o u t s t a n d i n g
in
order
to
a c c e p t b o t h e x p e c t e d and
Status
unexpected D A P S t a t u s m e s s a g e s .
messages a r e a l w a y s s e n t a s o r d i n a r y
( n o t I n t e r r u p t ) messages.

will

I f an e r r o r i s d e t e c t e d i n a S t a t u s message, e i t h e r during or a f t e r
s e t u p , a protocol e r r o r has occurred and t h e r e is nothing t h a t can be
done t o recover so t h e l i n k should be disconnected.
E r r o r s i n exchanging Configuration messages should be very r a r e s i n c e
the information i n Configuration messages w i l l g e n e r a l l y be "canned"
and of an informative n a t u r e . I f t h e accessed system d e t e c t s an e r r o r
i n t h e Configuration message, i t r e t u r n s a S t a t u s message and t h e
accessing system can e i t h e r r e t r y o r disconnect.
I f t h e accessing
system d e t e c t s an e r r o r , i t disconnects.
NOTE

I f , however, a Configuration message
appears t o be i n e r r o r because t h e
SYSCAP f i e l d i s too long and t h e DAP
version number i s g r e a t e r than t h a t t o
which t h e c u r r e n t software i s w r i t t e n ,
assume t h a t t h e SYSCAP f i e l d has been
extended i n t h e l a t e r v e r s i o n of DAP.
Ignore t h i s e r r o r .
T h i s is t h e only
The
time when an e r r o r i s ignored.
is
that
the
more
assumption
s o p h i s t i c a t e d DAP process uses only a
subset of t h e protocol and t h u s both
s e t s of software can work t o g e t h e r .

5.1.1 E r r o r s i n t h e Setup Sequence - The accessed process r e t u r n s a
S t a t u s message for e r r o r s d e t e c t e d i n each message (Configuration,
A t t r i b u t e s , Name, and Access). On receiving an e r r o r i n response t o
one of t h e s e messages, t h e r e a r e t h r e e p o s s i b i l i t i e s open t o the
accessing DAP process:
1.

Disconnect t h e l i n k .

Send t h e c o r r e c t e d message r e s p o n s i b l e f o r t h e e r r o r .
There
is no p o i n t i n sending t h e o r i g i n a l message u n l e s s t h e r e is
s u f f i c i e n t doubt t h a t t h e message was d e l i v e r e d p r o p e r l y o r
t h a t t h e e r r o r indicated was of a temporary n a t u r e . For
example, an attempt was made t o open a f i l e a l r e a d y open by
another process.

S t a r t a d i f f e r e n t access. A new a c c e s s u s u a l l y s t a r t s w i t h
an A t t r i b u t e s message, b u t i t could s t a r t w i t h an Access
message (where t h e type of a c c e s s does not r e q u i r e a t t r i b u t e s
such a s ERASE) or even a Configuration message.

If t h e user process t r i e s t o recover by sending a c o r r e c t e d message or
s t a r t i n g a new a c c e s s , t h e accessed DAP process can accept any of t h e
s e t u p messages i n response t o a S t a t u s message. Table 6 c o n t a i n s a
l i s t of responses t o s e t u p message e r r o r s . In t h i s t a b l e , Extended
A t t r i b u t e s messages a r e considered a s being A t t r i b u t e s messages and
Name messages p a r t of t h e Access message. When recovering from an
e r r o r i n an A t t r i b u t e s Extension message, t h e accessing process should
back up t o t h e A t t r i b u t e s message.

Table 6
Responses t o Setup Message E r r o r s
Responses
Error

Configuration
Message

Attributes
Message

Access
Message

Configuration Message

A t t r i b u t e s Message

Access Message

1 where:
0
1
2

I n v a l i d response.
Valid response.
Valid response only
a t t r i b u t e s message.

for

accesses

requiring

E r r o r s d e t e c t e d by t h e accessing process i n A t t r i b u t e s , Extended
A t t r i b u t e s , Name and Acknowledge messages cause the accessing process
t o disconnect t h e l o g i c a l l i n k t h u s terminating t h e access.
Setup Sequence - I f a timer i s used between s e t u p messages,
same timer should be s e t by t h e accessed process a f t e r an e r r o r
during setup. I f t h e timer e x p i r e s , a disconnect should be i n i t i a t e d .
5.1.2
this

The following conventions a r e used i n DAP message sequence diagrams i n
t h i s and subsequent s e c t i o n s :
Brackets [ 1 denote o p t i o n a l messages.
0

Messages on t h e l e f t s i d e of t h e arrows a r e from t h e accessing
process.

Messages on t h e r i g h t s i d e
accessed process.

the

arrow

are

NOTE

The message sequence diagrams i n t h i s
and
subsequent
sections
are
not
d e f i n i t i v e . However, although they do
not cover every s i t u a t i o n t h a t can a r i s e
with DAP remote f i l e a c c e s s , they should
be complete enough t o g i v e an idea of
what should be done i n those s i t u a t i o n s
not e x p l i c i t l y addressed.

sent

the

After a logical link is established, the setup sequence is a s follows:
1.

Configuration information exchange:
CONFIGURATION<------ >CONFIGURATION
NOTE
Both accessing and accessed processes
can
send
Configuration
messages
immediately on link establishment.
The
accessing
process
must
send
its
Configuration message immediately.

Setup for access:

1 EXTENDED
ATTRIBUTES]---- >

<------

ATTRIBUTES

<------

[ EXTENDED
ATTRIBUTES]

<------

[NAME (EXPANDED FILESPEC)]

<------

ACKNOWLEDGE

NOTES

Attributes
message
is
not
required when t h e Access message
s p e c i f i e s ERASE, RENAME, DIRECTORY
LIST,
or EXECUTE command f i l e . For
t h e s e types of a c c e s s , t h e accessed
process
returns
neither
the
Attributes
message
nor
the
Acknowledge
message
unless
specifically
requested
by
the
DISPLAY f i e l d . I f t h e DISPLAY f i e l d
is omitted from t h e Access message
and t h e f u n c t i o n i s OPEN, CREATE, o r
SUBMIT, t h e accessed process r e t u r n s
a Main A t t r i b u t e s message. When a
DISPLAY
f i e l d is p r e s e n t i n
an
Access message, t h e accessed process
r e t u r n s only t h e messages requested
by t h e DISPLAY f i e l d . When RENAME
i s s p e c i f i e d , follow t h e
Access
message by a Name message containing
the new name f o r t h e f i l e ( s e e
Section 5 . 2 . 8 ) .

Request t h e o p t i o n a l Name message
returned by t h e accessed process
a f t e r opening t h e f i l e by s e t t i n g a
b i t i n t h e DISPLAY f i e l d of t h e
Access message.
The Name message
c o n t a i n s t h e f i l e s p e c i f i c a t i o n of
the f i l e opened or c r e a t e d a f t e r a l l
the l o g i c a l names have been resolved
and d e f a u l t s a p p l i e d .

Error i n Configuration messages:
(a)

Disconnect a f t e r e r r o r d e t e c t e d :
CONFIGURATION------

<------

> ( e r r o r detected)
STATUS

DISCONNECT

(b)

Correcting erroneous message:
CONFIGURATION------

<------

(c)

>(error detected)
STATUS

I f the e r r o r i s i n t h e returned message:

( i n error)
DISCONNECT

<------

CONFIGURATION

Error in Attributes message:
(a) Disconnect after erroneous message:
ATTRIBUTES------ >(error detected)

<------

STATUS

DISCONNECT

(b)

Correcting erroneous message:
ATTRIBUTES------ >(error detected)

<------

STATUS

(c) Starting a new remote file access on the same link. The
new access shown must be one not requiring the Attributes
message as no valid attributes are currently in effect (the
former Attributes message contained an error). See Note 1 in
Section 5.1.2.
ATTRIBUTES------ >(error detected)

<------

STATUS

Error in Optional Extended Attributes message:
(a) Disconnect after erroneous message:

EXTENDED
ATTRIBUTES I----- >

EXTENDED
ATTRIBUTES n----- >(error detected)

<-----DISCONNECT

STATUS

(b) Correcting erroneous message (note that restart backs up
to the Attributes message) :

EXTENDED
ATTRIBUTES I----- >

EXTENDED
ATTRIBUTES n----- >(error detected)

<Ã‘--

STATUS

EXTENDED
ATTRIBUTES I----- >

EXTENDED
ATTRIBUTES n----- >

etc.
(c) Starting new access on same link:

EXTENDED
ATTRIBUTES I------ >

EXTENDED
ATTRIBUTES n------ >(error detected)

<------

STATUS

Error in Name message for default file specification:
(a) Disconnect after erroneous message:
NAME

- - >

DISCONNECT

(error detected)

(b) Correcting erroneous message:
NAME

------ >(error detected)
<------

STATUS

------ >(error detected)

NAME

<------

------ >
------ > I
------ >

ATTRIBUTES
[ NAME

ACCESS
7.

STATUS

Error in Access message:
(a) Disconnect after erroneous message:
ATTRIBUTES------ >
ACCESS

------ >(error detected)
<------

STATUS

DISCONNECT------ >

(b) Correcting erroneous message:

ACCESS

------ >(error detected)
<------

STATUS

------>(error detected)
<------

ATTRIBUTES------ >

STATUS

5.2

T r a n s f e r r i n g Data Over t h e Link

The message exchange sequence f o r t r a n s f e r r i n g d a t a over t h e l i n k
depends on t h e d i r e c t i o n of d a t a flow with r e s p e c t t o t h e accessing
and accessed systems. Data may be s e n t t o t h e accessing node a s i n a
r e t r i e v e o p e r a t i o n or from i t a s i n a s t o r e o p e r a t i o n .
Before d a t a t r a n s f e r can s t a r t , however, a d a t a stream m u s t be
i n i t i a t e d by sending a Control message ($CONNECT) a f t e r t h e f i l e i s
open.
With f i l e systems t h a t support m u l t i p l e
data
streams,
a d d i t i o n a l d a t a streams can be i n i t i a t e d w i t h more Control messages.
Multiple d a t a streams a r e d i f f e r e n t i a t e d by using t h e STREAMID number.
Data messages f o r a p a r t i c u l a r d a t a stream m u s t have t h e same STREAMID
number a s t h e Control message t h a t i n i t i a t e d t h e d a t a stream. I f t h e
STREAMID number is omitted, a d e f a u l t of 0 i s used.
The sequence f o r i n i t i a t i n g a d a t a stream i s a s follows:

<----

ACKNOWLEDGE

I f an e r r o r o c c u r s , a S t a t u s message i s returned i n s t e a d of an ACK. A
new d a t a stream can be i n i t i a t e d any time the f i l e i s open by using
the above message sequence.
NOTE

Multiple d a t a streams cannot be used i f
f i l e t r a n s f e r mode i s s p e c i f i e d i n the
RAC f i e l d of the Control message.
The
f i l e t r a n s f e r mode implies a s i n g l e d a t a
stream w i t h only d a t a
(no
control
messages) flowing over t h e l i n k . By
e l i m i n a t i n g Control messages, e f f i c i e n c y
is gained.
There a r e t h r e e c l a s s e s of S t a t u s message which can
accessed process during d a t a t r a n s f e r :
1.

sent

the

Successful. The accessed process r e t u r n s a success S t a t u s
message f o r d a t a t r a n s f e r r e d when not i n f i l e t r a n s f e r mode.
The s u c c e s s f u l S t a t u s messages synchronize DAP processes and
return information to the user.

In f i l e t r a n s f e r mode, d a t a i s p i p e l i n e d ,
s t a t u s messages a r e omitted f o r e f f i c i e n c y .
2.

and

successful

Warning. T h i s c l a s s of S t a t u s message i s s e n t t o t h e
accessing
process
when an o p e r a t i o n completes without
complete success. For example, t h i s message i s s e n t i f a
record was i n s e r t e d i n an indexed f i l e t h a t had a d u p l i c a t e
key.
Warning S t a t u s messages a r e always s e n t t o
the
accessing process provided t h e Configuration message s t a t e s
the accessing process supports them. After sending a warning
S t a t u s message, the accessed process suspends processing on
t h a t d a t a stream u n t i l i t r e c e i v e s a Continue Transfer
message ( o r t h e next Control message f o r Record R e t r i e v a l )
i n s t r u c t i n g i t t o resume processing or an Access Complete
message terminating t h e a c c e s s .
On receiving a warning
S t a t u s message, t h e accessing process e i t h e r sends a Continue
Transfer (Resume) t o continue d a t a t r a n s f e r , a Control
message, or an Access Complete i f i t wants t o terminate the
access.

Error.
This class of Status message is sent when an
operation was unable to complete at all, for example, if
there were a read error. When an event in this class occurs,
a Status message is always sent to the accessing process.
After sending the Status message, the accessed process
suspends processing on that data stream until it receives a
Continue Transfer message telling it what to do or an Access
Complete message terminating the access. On receiving an
error Status message, the accessing process either sends an
Access Complete to terminate the access or a Continue
Transfer if it wants to attempt recovery.

These three classes of Status message are differentiated by the
MACCODE field of the Status message (see Section 3.11 and Table 2 ) .
Status codes returned by the file system often assist in determining
which class of Status message, if any, should be sent on the
completion of each operation. However, ultimate responsibility for
the classification and mapping of file system status codes into DAP
Status messages resides with those who implement DAP server (accessed)
processes. The following subsections contain examples of the handling
of both warning and error Status messages.

For sequential file retrieval, the
5.2.1
Sequential File Retrieval
accessed system sends data records. Once the initial startup sequence
is completed and the data stream initiated, a single Control message
(Get) is sent to start data records flowing. Thereafter, the file
records are transmitted without waiting for any further DAP messages
to control sending messages. The lower level protocols perform all
flow control.
To specify sequential file retrieval, the accessing process specifies
sequential file access (or virtual block number file transfer) in the
Control (Get) message. The accessed process then sends file records
(or blocks) without waiting for any further DAP Control messages. In
contrast to sequential file retrieval, if sequential record access is
specified, the accessing process must send a Control message for each
record retrieved.
Data messages continue to arrive until one of the following occurs:
The end-of-file is reached on the accessed system.
An error occurs in accessing the file.
The accessing system decides it has completed its access.
In the first case, the last record sent in a data message is followed
by a Status message with end-of-file detected set. In the second
case, a Status message is sent when an error occurs in accessing the
original file.
If the accessing system receives a Status message with end-of-file, it
sends an Access Complete message and waits fo.r an Access Complete
(Response). It then either disconnects or initiates another access by
sending a setup sequence. If the accessing process receives a Status
message with either an error or warning, it may either send an Access
Complete Command and wait for an Access Complete (Response) or try to
recover with a Continue Transfer.

If the accessing system decides to terminate access prior
to
end-of-file, it sends an Access Complete (Close) and waits for an
Access Complete (Response) in return. In such cases, an accessing
system issuing an Access Complete (Close) may still receive one or
more records for the file, an end-of-file indication or even a Status
message due to the pipelining delay in the system. It should pass
over these records until an Access Complete (Response) is received.
It may then disconnect or access another file.
A number of possible sequential file retrieval
sequences
are
diagrammed below.
In each case, the accessing process sends the
messages to the left of the arrows.
The access process sends the
messages to the right of the arrows. Optional messages are bracketed.
1.

Retrieval until End-of-File
CONTROL (GET)------ >

(EOF) :

<------

RECORD 1

<------

RECORD n
NOTE

Transfer continues until End-of-File
error

<------

STATUS (End-of-File)

ACCOMP (CLOSE)------ >

<------

ACCOMP (RESPONSE)

The accessing process may now issue
access or disconnect the link.
2.

another

Retrieval until error or warning status:

<-----<------

RECORD n
STATUS

NOTE
The STATUS message occurs
to read record n+1.

while

trying

When an error is received, the accessing process can
of the following:
(a)

Request link termination.
ACCOMP (CLOSE)-------- >

<------

(b)

ACCOM P

( RESPONSE)

Request the information be sent again
CONTINUE (TRY AGAIN) ------ >

<------

RECORD n+l

one

(c)

Skip t h a t record and continue

----->
<------ RECORD n+2

CONTINUE (SKIP)

( d ) When a warning i s received, t h e accessing process can
request l i n k termination a s i n ( a ) above o r resume processing
by sending a Continue Transfer (Resume) message.

-----RECORD
>
n+1

CONTINUE (RESUME)

<------

R e t r i e v a l with a c c e s s termination:

<----

--->
<----

ACCOMP (CLOSE)

RECORD m

ACCOMP (RESPONSE)

The accessed process may s e t a timer following sending Access
Complete (Response).
I f n e i t h e r a Disconnect or another
may
message is received within t h e time i n t e r v a l , i t
disconnect t h e l i n k .
4.

R e t r i e v a l with checksum e r r o r on c l o s e :

<---- RECORD n
<---- STATUS ( EOF

--->
<---- STATUS

ACCOMP (CLOSE)

(checksum e r r o r )

ACCOMP(CL0SE)---- >

<---- ACCOMP (RESPONSE)

Do not send an Access Complete (Purge) t o t h e accessed
process a s i t purges the input f i l e . Sending the Access
Complete message w i t h t h e CHECK f i e l d causes a comparison of
the checksums.
I f t h e CHECK f i e l d i s omitted, checking is
by-passed.
See Section 5.5.2.

Sequential P i l e Storage/Append
In t h e s t o r e c a s e , d a t a is
5.2.2
s e n t t o the accessed system. Following t h e i n i t i a l i z a t i o n of t h e d a t a
stream, t h e accessing system sends a Control ( P u t ) message t o t e l l t h e
accessed process what t o do. The Control message i s followed b y f i l e
records using the Data message. The accessed system a c c e p t s t h e s e
messages and continues u n t i l t h e accessing system sends an Access
Complete ( C l o s e ) .
This causes a corresponding Access
Complete
Response t o be returned following s u c c e s s f u l f i l e c l o s u r e , or a S t a t u s
message t o be s e n t i f an e r r o r occurs i n c l o s i n g the f i l e or a
checksum f a i l u r e i s d e t e c t e d . For o t h e r than a checksum f a i l u r e , t h e
a c c e s s i s concluded and another access may s t a r t or t h e l i n k may be
disconnected.
I f a checksum f a i l u r e i s d e t e c t e d , another Access
Complete (without t h e CHECK f i e l d ) i s s e n t , e i t h e r c l o s e or purge, t o
terminate t h e access t h e way t h e user d e s i r e s .
To s p e c i f y s e q u e n t i a l f i l e s t o r a g e , t h e accessing process s p e c i f i e s
s e q u e n t i a l f i l e access i n t h e Control message together w i t h P u t . To
s p e c i f y s e q u e n t i a l f i l e append, t h e o p e r a t i o n s a r e the same except
" p o s i t i o n t o EOF" i s s p e c i f i e d i n t h e Control message i n a d d i t i o n t o
P u t and s e q u e n t i a l f i l e access.
A s w i t h sequential f i l e r e t r i e v a l ,
s e q u e n t i a l f i l e s t o r a g e implies t h e use of only one d a t a stream and no
Control messages a f t e r t h e i n i t i a l Control ( P u t ) message.

Example 1 below shows an o p t i o n a l Access Complete (End-of-Stream)
message
flushing
the pipeline before closing the f i l e .
This
resynchronizes t h e accessing and accessed processes.
Thus, e r r o r
handling i s e a s i e r i f an e r r o r occurs i n w r i t i n g t h e f i n a l records t o
t h e f i l e when t h e user i s s u e s a c l o s e command.
After t h e e r r o r is
returned t o t h e u s e r , he has t h e o p t i o n of purging t h e f i l e a s t h e
Access Complete (Close) i s not y e t i n t h e pipe.
I f an e r r o r occurs during record t r a n s f e r , t h e accessed system r e t u r n s
a S t a t u s message.
T h i s m u s t always be r e p l i e d t o with a Continue
message s e n t a s an I n t e r r u p t message (because of p o s s i b l e p i p e l i n i n g ) .
In a d d i t i o n , t o terminate t h e a c c e s s , send an Access Complete message.
A l i s t of s e q u e n t i a l f i l e s t o r a g e sequences follows.

In each sequence
t h e accessing process sends t h e messages t o t h e l e f t of t h e arrows.
The accessed process sends t h e messages t o t h e r i g h t of t h e arrows.
1.

S t o r e with no e r r o r s :

NOTE

Transfer continues
complete or e r r o r

until

access

------>
------ > 1 [<------ ACCOMP (RESPONSE)]
ACCOMP (CLOSE)
-<---------- > ACCOMP (RESPONSE)
RECORD n
[ACCOMP (EOS)

Error during t r a n s f e r :
(a)

Purge t h e new f i l e and terminate:

------ >
<------ STATUS
ACCOMP (PURGE) ------ >
CONTINUE (ABORT) ------ > ( INTERRUPT)

RECORD n

NOTE

receiving t h e
Continue
Transfer
I n t e r r u p t message, t h e accessed system
d i s c a r d s records u n t i l Access Complete
(Purge) i s received. I t then purges the
incomplete f i l e and r e t u r n s an Access
Complete.
On

<--Ã‘-

ACCOMP (RESPONSE)

Close the new f i l e and terminate:
ACCOMP (CLOSE)
CONTINUE (ABORT)

------ >
------ > ( INTERRUPT)
NOTE

The accessed system discards records
u n t i l the Access Complete (Close) is
received and then closes the incomplete
output f i l e .

<------

ACCOMP (RESPONSE)

Retry--the accessed system s t i l l has
caused the error i n i t s buffer:
CONTINUE (TRY A G A I N )
RECORD n + l

the

----------->> ( INTERRUPT)

Skip the record and continue:
CONTINUE (SKIP)
RECORD n + l

----------->> ( INTERRUPT)
NOTE

On an e r r o r , the accessed process does
not
issue
any more receives a f t e r
sending the Status message and before
receiving the Continue message, which
t e l l s i t what t o do. I f the accessing
process responds t o the error by sending
an interrupt Continue Transfer (Retry)
message and the r e t r y is successful, the
accessed process posts a receive and
c a r r i e s on w i t h the data transfer. If
the r e t r y f a i l s , another Status message
is

sent.

A Continue message with skip

always posts a receive and t r i e s t o
carry on having skipped the record which
caused the o r i g i n a l e r r o r .
For f i l e
transfer
store
or append, continue
messages m u s t be sent i n interrupt mode
as there may be data i n the pipeline.
3.

Warning during transfer:
(a)

Resume a f t e r receiving warning s t a t u s :

----->
<------ STATUS (WARNING)
CONTINUE(RESUME) ------> ( INTERRUPT)
-----RECORD n

RECORD n + l

record

which

(b)

To terminate t h e access a f t e r a warning, follow sequence
2 ( a ) above t o purge t h e output f i l e or 2 ( b ) t o keep t h e
output f i l e .
NOTE

After
sending
the
warning
Status
message, t h e accessed process i s s u e s no
an
more r e c e i v e s u n t i l i t r e c e i v e s
interrupt
Continue
Transfer message
i n s t r u c t i n g i t what t o do.
Stopping a s e q u e n t i a l f i l e s t o r a g e o p e r a t i o n before it is
complete and purging t h e incomplete f i l e on t h e accessed
system:

ACCOMP (PURGE)

------- > Purge t h e incomplete f i l e

<----ACCOMP

To save an incomplete f i l e
o p e r a t i o n s a r e a s i n S t e p 1.

(RESPONSE)

the

accessed

system,

the

Checksum e r r o r on close:

>
Record N---ACCOMP (CLOSE)

---- >
<----

STATUS (Checksum e r r o r )

The user can e i t h e r keep o r purge t h e erroneous output f i l e
by sending e i t h e r a c l o s e or purge Access Complete message
without t h e CHECK f i e l d .
5.2.3
Record R e t r i e v a l - Record r e t r i e v a l r e q u i r e s t h a t a Control
message ( w i t h a record key f o r random r e t r i e v a l ) be s e n t by t h e
accessing process f o r each record accessed.
To s p e c i f y record
r e t r i e v a l , t h e accessing process s e t s s e q u e n t i a l record a c c e s s , keyed
access o r Record F i l e Address ( R F A ) access i n t h e Control message.
Block mode t r a n s f e r , s i m i l a r t o record r e t r i e v a l , is s p e c i f i e d by
s e t t i n g V i r t u a l Block Number (VBN) access.

For keyed, VBN, o r RFA a c c e s s , t h e sequence is a s follows:
CONTROL ( g e t record w i t h Key n)

--->
<---- RECORD n, STATUS

CONTROL ( g e t record w i t h Key m)----

<----

RECORD m , STATUS

For sequential record access, the state operation is as follows:
CONTROL (get sequential)--------- >

<----

CONTROL (get sequential)-------- >

<----

RECORD k, STATUS
RECORD k+1, STATUS

Once the location of a particular record in a file is found using
random access, the user frequently wants to get subsequent records
sequentially. To do this, switch the access mode from keyed or RFA to
sequential in the Control message, and issue a Get. (With RMS
systems, the user is free to switch access modes according to the RMS
rules. )
CONTROL (get record with Key r)---- >

<---- RECORD r, STATUS

CONTROL (get sequential)

------->
<---- RECORD r+1, STATUS

Once a particular record in a file is found, it is possible
transfer the remainder of the file in sequential file access mode.
CONTROL (get record with key t)---- >

<----

RECORD t, STATUS

CONTROL (sequential file access, get)----- >
<---- RECORD t+1, STATUS
<---- RECORD t+2, STATUS

to end-of-file
Error handling for sequential record retrieval is similar to error
handling for sequential file retrieval. The handling of warnings is
easier, however. In order to continue processing, the accessing
process sends a Control (Get). A Contine Transfer (Resume) is not
necessary, but should be ignored if received.
Error handling for random record retrieval is similar to that for
sequential file retrieval.
However, the Continue (Skip) recovery
option, which is valid for sequential retrieval, is not valid for
random retrieval.
When a control request specifies a nonexistent
record while doing random record retrieval, the accessed process will
return an appropriate error message (for example, record number out of
range or record not found).
5.2.4
Record Store - This is similar to sequential file store in
messages exchanged.
The access message specifies whether to open an
existing file or create and open a new file. The Control message must
specify Put access.
For record storage, the accessing process may
specify sequential record access, or keyed access.
Optionally, VBN
access may also be used.

For relative files, the data messages must include the relative record
number field specifying the number of the record (RECNUM). For hashed
files where the user is supplying his own hash code (RB$HSH set in the
ROP field of a Control message), RECNUM contains the hash code. In
all other cases, the contents of RECNUM are ignored and will probably
be set null to minimize data transmission overhead. For sequential
files, records are written starting at the current position within the
file.

The sequence of records to be stored may be preceded by a Control
(Put) message if it is necessary to change record options or access
mode from the current value. Optionally, each record to be stored may
be preceded by a Control (Put) message. This is inefficient, however,
since it doubles the number of DAP messages transmitted. When storing
a record, if the Data message is preceded by a Control message that
contains a record number in the KEY field and the Data message also
contains a record number in the RECNUM field, then the record number
in the RECNUM field will be used.
The sequence for record storage with return of status is as follows:
RECORD n -------- >
RECORD n+1 ------ >

Section 5.2.2 describes error-handling. Note that a warning Status
message requires an interrupt Continue Transfer (Resume) (or Abort) to
restart processing because of possible pipelining problems.
Continue
(Skip) causes the accessed process to ignore the record which caused
the error and go on to process the next DAP message.
5.2.5 Append to Existing Pile - The append operation is identical to
sequential store and applies only to sequential files. The accessed
system places the records at the logical end of the file. The Control
message sets the position to EOF. The sequence is as follows:
RECORD I-------- >

RECORD 2-------- >

5.2.6
Deleting a File - The delete operation (Erase) does not cause
any file data to be transferred, but does manipulate file structures.
Deleting a file does not require an Attributes message in the setup
sequence.
The message sequence for the delete operation is as follows:

ACCESS (ERASE)

----- >
<-----

ACCOMP (RESPONSE)
or
<----- STATUS

5.2.7
Coaunand/Batch Execution Files
The Data
Access
Protocol
includes commands for the transfer and submission of files to a batch
processing
facility
or
command
interpreter.
The
"submit-as-command-file" request in the Access message requests the
storage of the data that follows in a temporary file.
This request
also indicates submission of the file to a batch-type facility upon
access completion (closing of the file). The batch facility deletes
the file following execution. DAP does not respond to any feedback
from the batch facility.
DAP does not guarantee that the file
actually executes in the batch monitor. DAP transfers the file using
sequential file storage (Section 5.2.2).
The "execute-as-command-file" requests the submission of the specified
file to the batch facility only. No data follows this command. The
specified file is previously established on the accessed system.
The
file is not deleted following execution by the batch facility, so that
the sequence "store," and "execute-command-file" will transfer a file,
submit it and retain the file for later use. The sequence for
"submit-as-command-file"
is
identical
to
"store,"
while
the
"execute-command-file" is identical to Erase.
NOTE
Since errors are not returned to the
originating node automatically, a test
for errors might be included in indirect
command
files.
Upon
error
or
completion, a suitable message can be
returned to the originating node.
Renaming a File - The rename operation does not cause the
transfer of any file data. However, it does require the transmission
of two file specifications. The old name of the file is in the Access
message;
the new name for the file is in t h e Name message following
the Access message. Rename does not require an Attributes message in
the set up sequence.
5.2.8

The message sequence for the rename operation is as follows:

ACCESS (RENAME)------ >

------>

NAME (FILESPEC)

<---------<----------

ACCOMP (RESPONSE)
or
STATUS

5.2.9
Extending Piles - File systems often offer an automatic file
extension facility to extend an existing file when space runs out but
there is more data to be written to the file. However, automatic file
extension usually offers little control over the size and placement of
file extensions.

Another method of extending a file is to use the explicit $EXTEND code
of the Control message where a file system supports user directed
extension. User directed file extension is initiated after the file
is open. The DAP state operations are:
data traffic on link

ALLOC

1 ------ >

ALLOC

n ------ >

CONTROL (EXTEND)------ >

continue data traffic on link
Precede the Control (Extend) message by one or more ALLOC (Allocation
Attributes Extension) messages specifying the type of extension
desired. Return a corresponding number of ALLOC messages, specifying
the extensions performed.
Return a Status message terminating the
string of returned ALLOC messages.
If an error occurs, a Status
message will contain the error code.
a
means
of
5.2.10
Display Attributes - This command provides
obtaining attribute information about a file. It is specifically for
use with RMS file systems. If this command is used, the accessing
node must specify which groups of attributes it wants. It does this
by setting the appropriate bits in the DISPLAY field of the Control
message sent to the remote node. In the case of the allocation and
key definition groups of attributes, the appropriate Key Definition
and Allocation Attributes Extension messages precede the Control
message to indicate for which Keys of reference or which areas
attributes are required.

The state operations for display are:
[ATTRIBUTES
EXTENSION------------MESSAGES]

CONTROL (Display)------ >

<---------

[ATTRIBUTES and ATTRIBUTES EXTENSION
MESSAGES AS REQUIRED]

<---------

STATUS

5.2.11
Directory List - A directory or multiple directory listing
request causes the accessed process to return the file attributes o f
the files specified in the FILESPEC field o f the Access message
requesting
the
directory
list.
The accessed process returns
attributes using the Attributes and Attributes Extension messages.
The accessing process can specify which Attributes messages it Wants
by setting the appropriate bit(s) in the DISPLAY field of the Access
message.
If the DISPLAY field requests the Name message (bit 8 1 , the
resultant file name is returned with the Attributes messages in a Name
message.
This Name message is in addition to the Name messages shown
in the state operations below.
The file specification in the Access message may contain
cards" a s are recognized by the accessed process.

such

"wild

As can be seen from the state operations for directory list below, a
Name message for the file the Attributes messages describe precedes
each group of Attributes messages. If no bits in the DISPLAY field of
the requesting Access message are set, only the Name messages are sent
(no Attributes messages). A Name message precedes all the files in a
given directory.
Optionally, if all the directories for which a
listing i s requested d o not reside o n the same volume-set
(or
structure),
a
Name message precedes the directories for each
volume-set.
The Name message indicates which volume-set the following
directories are on.
The state operations for directory listing are:

[<----------NAME

(VOLUME-SET)]

<----------

NAME (DIRECTORY)

<----------

NAME (FILE)

[<----------

ATTRIBUTES]

[<----------

ATTRIBUTES EXTENSION]

[<----------

ATTRIBUTES EXTENSION]

<-----------

NAME (FILE)

[<----------

ATTRIBUTES]

[<----------

ATTRIBUTES EXTENSION]

Ã‡---------

ATTRIBUTES EXTENSION]

<-----------

NAME (FILE)

[<----------

ATTRIBUTES]

[<----------

ATTRIBUTES EXTENSION]

[<----------

ATTRIBUTES EXTENSION]

<-----------

NAME (DIRECTORY)

<-----------

ACCOMP (RESPONSE)

The accessing process may terminate a directory listing at anytime by
sending an Access Complete(C1ose). This causes the accessed process
to send no more Name or Attributes messages, to finish its operation
(for example, close any files it may have open) and finally to return
Note that due to pipelining, the
an Access Complete (Response)
accessing process may receive several Attributes and/or Name messages
before receiving an Access Complete(Response) after it sends an Access
Complete (Close)

Errors occurring during a directory listing result from trying to
obtain information to generate either a Name message or an Attributes
or Attributes Extension message when reading a directory or the
attributes of a file. On a gross level, errors will be either read
errors, access protection violations, or non-existent attributes (for
some reason, the attributes for a file cannot be found or do not
exist). Read errors are handled by using the Continue Transfer (Try
again or Skip) or Access Complete (Close). Protection violations and
non-existent attributes errors are handled using the Continue Transfer
(Skip) or Access Complete (Close).
Continue Transfer (Try again)
usually just returns the same error.
Access Complete (Close) terminates the directory listing, closes any
open files and leaves the link in a state where another DAP access may
be started. Continue Transfer (Try again) repeats the operation that
failed.
Continue Transfer (Skip) causes the accessed process to skip
over the operation causing the error, and attempt to recover the
listing that lost some information. For example, this operation tries
to read subsequent blocks in the directory, trying to get the next
file name.
Or the operation may attempt to read the next block
containing attributes for the current file. In some cases, it may not
be possible to recover using Continue Transfer (Skip).

The following
listing:
1.

are

examples

error

handling

for