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Document:	Data Access Protocol Functional Specification
Order Number:	AA-K177A-TK
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Pages:	105
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Order No . AA-K 177 A-TK

·
DECnet
DIGITAL Network Architecture

Data Access Protocol
Functional Specification
(DAP)
Version 5.6.0

DEenet
DIGITAL Network Architecture
(Phase III)
Data Access Protocol
Functional Specification
(DAP)
Order No. AA-K177 A-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 · maynard, 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:

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CONTENTS

Page
1.0
2.0
2.1
2.2
2.3

3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9

3.10
3.11
3.12
3.13
3.14
3.15
3.16
3.17
3.18
4.0
4.1
4.2
4.2.1
4.2.2
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.4
4.4.1
4.4.2
4.4.3
4.4.4
5.0
5.1
5.1.1
5.1. 2
5.2
5.2.1
5.2.2
5.2.3
5.2.4
5.2.5
5.2.6
5.2.7
5.2.8

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
Date and Time Attributes Extension Message
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

1
2
2
2
4
6
6

7
11
14
21
25
29
29
29
31
31
45
46
48
48
49
51
51
52
52
52
53
53
54
54
54
54
55
55
55
55
55
56
58
58
60
61
67
68.

70
73
74
75
75
76
76

CONTENTS (Cont.)

Page
Extending Files
Display Attributes
Directory List
Rewind Data Stream
Truncate File
Free Buckets
Space Forward or Backward
Flush I/O 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

5.2.9
5.2.10
5.2.11
5.2.12
5.2.13
5.2.14
5.2.15
5.2.16
5.2.17
5.2.18
5.2.19
5.2.20
5.2.20.1
5.2.20.2
5.2.20.3
5.2.20.4
5.3
5.4
5.5
5.5.1
5.5.2
5.6
5.6.1
APPENDIX A
APPENDIX B

P.l
B.2

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

76
77

78
81
81
81
82
82
82
83
83
84
85
87
89
90
90
90
90
90
91
91
91
93
95
95
95
97

GLOSSARY

FIGURES
FIGURE 1
2

Interrelationship of DNA Layers
Typical DAP Message Exchange (Sequential File
Retrieval)

3
5

TABLES
TABLE

1
2
3
4
5
6

DAP Messages
MACCODE Field Values
MICCODE Field Values for Use with MAC CO DE Values of 2,
10, and 11 Octal
MICCODE Field Values for Use with MACCODE Values of 0,
1, 4, 5, 6, and 7 Octal
MICCODE Field Values (with MACCODE Value of 12 Octal)
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 III 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-Kl78A-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

1.0.0,

DNA Transport Functional Specification, Version 1.3.0, Order
AA-K180A-TK
The following overview document for
these specifications
introduction to the structure and functions of DNA.
DNA General Description, Order No.

AA-Kl79A-TK

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 6f the I/O structure of the operat~ng system
being accessed.

2.1

DAP Functions

Within DECnet, DIGITAL opera~ing ~"qtems can emplpy DAP to provide the
following remote f~~e access functions:

2.2

•

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 directoriep.

Relationship to the DIGITAL Network Architecture

The DIGITAL Network Architecture provides a modular design for DECnet.
Its functional components are d~fined 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
system-dependent aspects of logical link communication.

defines

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 serVlce 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.

User Modules

User Layer

Network
Management Layer

----~-----Network

Application Layer

--- .... -----Session Control Layer

Network Services Layer

Transport Layer

Data Link Layer

Physical Link Layer

Horizontal arrows show direct access for control and examination of parameters, counters, etc. Vertical and
curved arrows show interfaces between layers for normal user operations such as file access, down-line load,
up-line dump, end-to-end looping, and logical link usage.

Figure 1

Interrelationship of DNA Layers

2.3

Generic Model

As an aid toward understanding the Data Access Protocol, this section
contains a gener ic model. This mo'del 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
OAP Messages
Message

Function

Configuration

Exchanges
system
capability
and
configuration
information
between
OAP-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

is
Provides information on
how
data
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

of, 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
Description

Messages
Configuration Message

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

Configuration Message

•

Configuration
Information
Returned
Attributes Message

Access Message

File Characteristics
(e.g., Type, Blk Size
and Record Size)
Access Request

Attributes Message
Actual File Characteristics Returned
Acknowledge Message

Set up Data Stream

Data Stream)
'" Control (Initiate
Message'

•

Acknowledge Message
Data Stream Established
Control (Get) Message

Request Start of Data
Transfer and Mode of
Transfer

.
..
..

Data Sent in Records

••
•
Record N
Status Message

End-of-File Indicated

Request to Term inate

Figure 2

Record 1

Access Complete Message

•

File Opened

Access Complete Response
Request Completed Successfully

Typical DAP Message Exchange (Sequential File Retrieval)
5

3.0

MESSAGE FORMATS

3.1

Notation

The

follo~ing

notation is used to describe the DA? 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"
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.

meaning

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 I-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 fi~ld 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:
1.

If length and coding are omitted, field represents
of subfields specified in the description.

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 OAP
messages can be omitted so the default can be used:

3.2

number

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).

If a field is present with a zero value,
default value. Use the value zero.
6.

omitted

not

use

the

Brackets [ 1 denote optional fields.

General Message Format

All DAP messages have the following form:
OPERATOR

OPERAND

where:
OPERATOR

This field describes the characteristics and type of
message.
It is divided into seven subfields: TYPE,
FLAGS, STREAMID, LENGTH, LEN256, BIrCNT, 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.

FLAGS (EX-5)

The DAP mess~ge flags.
Bits in this
extensible
field
are
currently
defined as follows:
Bit(s)

STREAMID(l)

Meaning (When Set)

Str~am identification
present.

Length field present.

If bit 1
(length
field
present)
is
set,
field
LEN256 is present and the
length field is in effect 2
bytes long.
Illegal if bit
1 not set.

The BITCNT field is present.

Reserved (0).

SYSPEC field present.

If set, this is a segmented
message and this is not the
last segment of the message.
The
next
message
will
contain the next segment of
the full message.
The next
message must be of the same
type as this message.
Refer
to the SYSCAP field
of the
Configuration message to see
if
this
facility
is
supported.

field

The stream
identification
field.
This field is included only if bit 0
of the FLAGS field
is set.
This
field
is used to allow a single user
to have multiple data streams in use
for a
single open file.
All data
streams use the same logical link
(they
multiplex
on the STREAMID
number) .
If the STREAMID number is omitted, it
is assumed to be zero. Not all file
systems are capable of supporting
multiple data streams from a single
file.

LENGTH(l)

Denotes the length of the OPERAND
field
(number of 8-bit bytes). This
field is optional.
It is included
only if bit 1 of the FLAGS field is
set. Two or more DAP messages may be
blocked together
into one Session
Control buffer (usually for
reasons
of efficiency).
If DAP messages are
blocked, the LENGTH field must be
present so the end of one message and
start of the next can be found.

Messages between 0 and 255 bytes long
may be blocked using only the LENGTH
field.
DAP messages whose operand
length is between 256 and 64K bytes
may be blocked only if both bits 1
and 2 of FLAGS are set.
Lengths
greater
than 64K bytes are sent
unblocked or as the last part of a
blocked message.
LEN256(1)

Contains the most significant byte of
a two byte OPERAND length if bit 2 of
FLAGS is set.
LENGTH contains the
least significant byte.
If LEN256 is
present, LENGTH must also be present.

BITCNT(l)

This field is valid only with the
Data
message.
If
present,
it
contains a number in the range 0-7
which is the number of unused bits in
the final 8-bit byte of the message.
It is required only when transmitting
data which does not completely fill
the final 8-bit frame of a Data
message.
This
is
useful
when
accessing files whose byte size is
not a multiple of eight. See Section
4.4.3.

SYSPEC(I-255)

This optional field is the system
specific field.
It can only be used
for
file
access
between
two
homogeneous systems.
This field is
included only if bit 5 of the FLAGS
field is set.
If it is used between
hetrogeneous systems, it will produce
a fatal error and the access will be
aborted.
Between
homogeneous
systems, this field can be used for
passing system specific information
as defined by the system. The SYSPEC
field can not be used with
the
Configuration message.
This field
must not
be
used
for
passing
information common to more than one
system.
NOTE
If this field is used, all
system
specific
functions
must be registered with the
architecture
group
within
DECnet
in
advance
of
certification.

OPERANO

The information field for OAP messages.
on the TYPE field.
NOTE
Typically, one
OAP-speaking
process
sends one or more OAP 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 OAP messages.
OAP messages can
be blocked in one of two ways:
l.

The first process blocks and sends
OAP messages up to the point where
response from
the
i t expects a
cooperating process.
I t then waits
for the response.

The first process blocks and sends
OAP
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 OAP messages, process
some of them, send a response and
then
continue
processing
OAP
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 OAP messages.
OAP 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.

It is dependent

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:
ICONFIGIBUFSIZIOSTYPEI FILESYSIVERSIONISYSCAPI
where:
The OPERATOR field with TYPE

CONFIG

= 1.

BUFSIZ(2)

The maximum buffer size (in bytes) of the sending
system for message exchange. The two cooperating
DAP speaking processes will use the lesser 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.

OSTYPE(l)

system) .
Operating system type
(the sending
Values in the range 1-191 are reserved for
reserved
for
DIGITAL
use;
192-255
are
user-specified operating systems.
Value
0
1
2
3
4

5
6

7
8
9
10
11

12
l3

OS Type
Illegal
RT-ll
RSTS/E
RSX-llS
RSX-llM
RSX-llD
lAS
VAX/VMS
TOPS-20
TOPS-10
RTS-8
OS-8
RSX-llM+
COPOS/ll (TOPS-20 front-end)

FILESYS(l)

File system type (of the file system being used
by the process sending this message). Values in
the range. 1-191 ar,e reserved for DIGITAL use;
192-255 are reserved for user-specified file
systems.'
Value
0
1
2

3
4
5
6
7

8
9

VERSION

System
Illegal
RMS-ll
RMS-20
RMS-32
FCS-ll
RT-ll
No file system supported
TOPS-20
TOPS-lf2J
OS-8

A field identifying the
version numbers.
This
follows:
VERNUM I ECONUM

protocol and software
field is subdivided as

USRNUM I SOFTVERI USRSOFT

where:
VERNUM(l)

DAP version number. This is the
same as the first digit of the
protocol version number.

ECONUM(l)

DAP ECO
(Modification)
number.
This is the same as the second
digit of the protocol version
number.

USRNUM(l)

: B

Customer modification level
DAP. Set to 0 by DIGITAL.

SOFTVER(l)

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

USRSOFT(l)

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

SYSCAP(EX-12)

Generic system capabilities.
as follows:

These

are

defined

Bit

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.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27

Bit

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 deletiun 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)

29
30
31
32
33
34
35
36
37
38
39
40
41

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:
I ATTRIBIATTMENUIOATATYPEIORGIRFMIRATIBLSIMRSIALQIBKSIFSzl
I MRNIRUNSYSIDEQIFOpIBszIOEv\sDcILRLI HBKIEBK/FFBISBNI

!14

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
ATTMENU(EX-6)

The OPERATOR field with TYPE
BM

= 2.

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.

Bit

Meaning (When Set)

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

DATATYPE
ORG
RFM
RAT
BLS
MRS
ALQ
BKS
FSZ
MRN
RUNSYS
DEQ
FOP
BSZ
DEV
SDC (reserved)
LRL
HBK
EBK
FFB
SBN

18
19
20
BM

DATATYPE(EX-2)

The type 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.
Bit

Meaning (When Set)

0
1
2
3
4
5
6

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

NOTES
1.

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.
16

ORG(l)

RFM(l)

Attributes of the file being accessed.
attributes are as follows:

Value
(octal)

Meaning

0
20
40
60

FB$SEQi
FB$RELi
FB$IDXi
FB$HSHi

FB$UDFi Undefined record
format.
FB$FIXi Fixed-length records
(default) .
FB$VARi Variable-length
records.
FB$VFCi Variable with fixed
control format.
FB$S™i ASCII Stream Format.

0
1
2

3
4

Information
about
individual records.
set 0.
Bit
0
1
2

3
4

5
6
7

transferred.

Meaning

Value

RAT(EX-3)

Sequential (default) .
Relative.
Indexed.
Hashed (reserved) .

Format of the records being
These formats are as follows:

These

the
attributes
of
The default is all bits

Meaning (When Set)
contain
FORTRAN
Records
FB$FTNi
carriage control (see Note 1) •
FB$CRi Records have an implied LF/CR
envelope.
FB$PRNi Print file carriage control
where
pre- and post-fix carriage
control information is stored in the
field of files in
fixed
header
variable with fixed control (VFC)
format.
FB$BLKi Records that do not span
blocks (see Note 2) •
Records have embedded format control
(see Note 3) .
Intended for COBOL carriage control
(reserved) .
FB$LSAi Line-sequenced ASCII Format.
MACYll format (note 4) •

NOTES
1.

FORTRAN Carriage Control. For line
printers and some terminals, treat
the first character of each record
as a carriage control character.

This bit, when set, informs the
system that the record length should
not exceed the
physical
device
blocking size.
with some systems
and on some
devices
(for
I/O
example, disk and magnetic tape)
this may be a factor in determining
actual
format used on the
the
device.

This bit, when set, informs the
system that records in the file may
contain format control characters
(LF, VT, and so on) .

MACYll format is a standard used on
10's
and
20's
to store files
destined for PDP-II's. These files
usually contain 8-bit data such as
object code output by
a
cross
compiler.

BLS(2)

Physical block size in bytes on media.
The
default value is 512. The actual byte size
is as specified by field BSZ.

MRS (2)

The length of each file record in number of
bytes.
For variable-length records, this
field specifies the maximum record size.
When the accessed process receives the MRS
(maximum record size), it must check it
against the length of its buffer. If the
buffer will not accommodate this size record,
the accessed process should return an error.
A zero value means no checking is performed
on record size. MRS is used by the various
file systems in a system-dependent manner.
The default is 0.

ALQ(I-5)

This field specifies the allocation quantity
in blocks.
For file creation, it specifies
the initial size of the new file. The actual
size of the new file is returned in this
field~
The default is 0.
NOTE
Ignore this value on opening existing
files. Use this field only to return
the file si ze.

BKS(l)

Bucket size in blocks, Used for access to
relative (not RMS-20), hashed and indexed
files with RMS. The default is 0 (see Note 2
at the top of Section 3.4).
18

FSZ{l)

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).

MRN (I-5)

Maximum record number for file (for relative
files only).
If set to 0, checking is
suppressed. The default is 0.

RUNSYS (I-40)

DEQ (2)

FOP (EX-6)

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.

The

Bit

Meaning (When Set)

FB$RWOi Rewind on open.
FB$RWCi Rewind on close.
Reserved (0).
FB$POSi Position magnetic tape just
past the most recently
created file.
FB$DLKi Do not lock file if not
properly closed.
Reserved (0).
File Locked.
FB$CTGi A contiguous file creation
or extension required.
FB$SUPi Supersede existing file on
create.
FB$NEFi Do not position to EOF on
opening magnetic tape file
for PUT.
FB$TMPi Create temporary file.
FB$MKDi Create temporary file and
mark for delete on close.
Reserved (0).
FB$DMOi Rewind and dismount
magnetic tape on close.
FB$WCKi Enable write checking.
FB$RCKi Enable Read checking.
FB$CIFi Create new file if one by
the same name does not
exist. If one does exist,
open the highest version
of the file.
FB$LKOi Override file lock on open
(reserved) .
FB$SQOi Sequential access only.
FB$MXVi Maximize version number.
FB$SP~i Spool file to line printer
(one copy only) on close.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

17
18
19
20

Bit

Meaning (When Set)

FB$SCF; Submit as command file on
close.
FB$DLT; 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
(wri te accessed SEQ files) .
FB$OFP; Output file parse (the name
type will be preserved
until overridden).

22
23

24
25
26
27

BSZ(l)

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.
DEV(EX-6)

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.
Bit

Meaning (When Set)

3
4
5

FB$REC;
FB$CCL;
FB$TRM;
FB$MDI;
FB$SDI;
FB$SQDi

6
7

FB$FOD;

8
9
10
11

FB$SPLi
FB$MNTi
FB$DMTi

1
2

Record oriented.
Carriage. control device.
Terminal.
Directory structured.
Single directory only.
Sequential, block oriented (for
example, magnetic tape).
Null device.
A file-oriented device (for
example, a disk or magnetic
tape) .
Device can be shared.
Device is being spooled.
Device is currently mounted.
Device is marked for dismount.

Bit
12
13
14

15
16
17
18
19
20
21
22
23
24
25

Meaning (When Set)
FB$ALL; Device is allocated.
FB$IDV; Device is capable of providing
input.
FB$ODV; Device is capable of providing
output.
FB$SWL; 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.

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

Spooling device characteristics.
SOC uses
the same bit definitions as in the DEV field.
If the file
is spooled,
SOC 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.

LRL (2)

Longest record length.
record in the file.

Length of the longest

HBK(I-S)

Highest virtual block allocated to the file.

EBK(I-S)

End of file virtual block number.

FFB(2)
SBN (1-5)

3.5

First free byte in end of
size as defined in BSZ.

Starting logical block
contiguous;
else 0.

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:
The OPERATOR field with TYPE = 3.

ACCESS
ACCFUNC(I)

The request code specifying the
performed is as follows:

I
2

operation

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

3
4

S
6

7
8

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
For example, the file
node for file creation.
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-S)

The access options are as follows:
Bit

Meaning (When Set)

I/O errors are non-fatal. A record may be
skipped or repeated as specified by the
Continue Transfer message.
I f not
set,
I/O errors are fatal and terminate the
access.

A status
message
will
returned
be
following each record sent to the accessed
process in
the
record
access
mode
(reserved) .

FILESPEC
(1-255)

FAC(EX-3)

Bit

Meaning (When Set)

A 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.

The file specification in the format required by
the remote node.
A null file
specification
assumes the meaning of a null file specification
on the target node.

The file access operations a user requires:
Bit
0

1
2

3
4

5
6

Meaning (When Set)
FB$PUT;
FB$GET;
FB$DEL;
FB$UPD;
FB$TRN;
FB$BIO;
FB$BRO;

Put access.
Get access (default) .
Delete access.
Update access.
Truncate access.
Block I/O acess (see Note) .
Support switching between
block and record I/O.
NOTE

FB$REA
FB$WRT

FB$BIO!FB$GET; Block I/O Read access.
FB$BIO!FB$PUTi Block I/O Write access.

SHR (EX- 3)

Operations shared with other users:
Bit

Meaning (When Set)

0
1
2
3
4
5

FB$PUT;
FB$GET;
FB$DEL;
FB$UPD;
FB$MSE;
FB$UPI;

DISPLAY(EX-4): BM

Put access.
Get access (default) .
Delete access.
Update access.
Enable mUlti-stream access.
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 log ical name (s) ,
this will return the file specification
of file opened without logical names.

1
2
3
4
5
6
7
8

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(I-40): B

Password required to obtain access to file.

3.6

Control Message

The Control message sends control type information to a
The Control message format is as follows:

file

system.

where:
CONTROL
CTLFUNC(l)

The OPERATOR field with TYPE = 4.
B

Specific control information:
Value

Meaning

$GET (o~ $READ for block I/O) ~ Get record
(or
block) .
If random access to a
relative file is made, the KEY field
contains the record number.
If a random
access to an indexed file is made, KEY
contains the key.
If sequential access is
employed, get the next record (default).

$CONNECT~
Initiate data
stream.
If
multiple data streams are used, they are
multiplexed on the STREAMID number.
The
STREAMID number in the Control message
initiates a data stream.
If the STREAMID
number is omitted, assume a default of
zero.

$UPDATE~

Update
current
record.
Indicates
to the accessed system the
intent of the accessing system to update
the currently positioned record with the
next data transmission.

$PUT (or $WRITE for block I/O) ~ Indicates
to
the
accessed
system,
that
the
information to follow should be written
into the file.

$DELETE~

Delete current record.

$REWIND~

Rewind file.

$TRUNCATE~
Truncate
file.
writes
end-of-file at current position.
Used
with sequential files only.

$MODIFY~

Change

file

attributes

(reserved) .
9

$RELEASE~
Unlock record specified
by
Record
File
Address
in
KEY
field
(reserved) .

$FREE~
Unlock all locked records for this
data stream.

Reserved.

Meaning

Value

$FLUSH~

buffers
stream.

CTLMENU(EX-4) :BM

modified
for this

I/O
data

$NXTVOL~

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

$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 I/O only.

SPACE BACKWARD~ Backward space the file
by the number of blocks specified by KEY
below. Block I/O only.

Perform
start-of-next-volume
(reserved) •

end-of-volume
and
processing
but

the.

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.
Bit

Field

RAC
KEY
KRF
ROP
HSH (reserved)
DISPLAY (reserved)

1
2
3
4
5
RAC(l)

Write out all
and attributes

Sets the access mode.
If this field is not
present,
retain the option in force for the last
access. The default is 0 if not set previously.
Value

o
1
2

3
4

Meaning
RB$SEQ~
RB$KEY~

Sequential record access.
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
explici t
Control
(Get)
or
(Put)
is
required to start data moving.
26

KEY (I-255)

File or Mode

Key

Relative Files
Indexed Files
Hashed Files
Record File Address
Access Mode
Block Mode Access

Record Number
Record Key
Record Key

Recovery

Record File Address
virtual Block Number
(binary, range 1 to n)
Input File Checkpoint
Locater

Right justify non 8-bit quantities in the KEY
field with the high order and unused bits set to
zero.
If the key consists of
7-bit
ASCII
characters,
right justify each 7-bit character in
an 8-bit frame as is usual for the transmission of
ASCII characters.
KRF(l)

ROP(EX-6)

Key of reference.
If this field is not present,
do not change the key of reference.
Default is
primary if never set.

Value

Meaning

0
1-254

Primary key
Secondary key indicator

Optional record processing features.
If this
field
is not present, retain the options in force
for the last access.
Bit

Meaning (When Set)

RB$EOF; position to EOF.
RB$FDL; Fast delete--mark record
deleted but do not remove
pointers from index.
RB$UIF; $PUT's update existing
records in relative files.
RB$HSH; Use hash code in HSH
(reserved) .
RB$LOA; Follow fill quantities.
RB$ULK; Manual locking/unlocking
(reserved) .
RB$TPT; Truncate Put--writes EOF
at current position. SEQ files
only (Put also occurs).
RB$RAH; Read ahead.
RB$WBH; write behind.
RB$KGE; Key is >=.
RB$KGT; Key is >.
RB$NLK; Do not lock record.
RB$RLK; Read a locked record (read
only) .
RB$BIO; Block I/O.
RB$LIM; Compare for key limit
reached (reserved).
RB$NXR; Non-existent record
processing (reserved).

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
HSH(I-5) : B
(Reserved for
future use)

Hash code if keyed
access on direct file
employed and the user is doing hashing.

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

Attributes messages to be returned in response
to a request to retrieve the file's attributes
are:
Bit
0

1
2
3
4
5
6
7
8

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
opened
using
specification--if
file
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
particular
message
type
(as
indicated
in
the
Configuration
message from the accessed process)
does not request that message type
in the DISPLAY field of 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 I/O transfer. Normally, the
accessed process informs the accessing process of an I/O 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:

ICONTRAN I CONFUNC I
where:
The OPERATOR field with TYPE

CONTRAN
CONFUNC(l)

This field specifies the recovery action to be taken:
Meaning

Value

Try again.
Skip and continue.
(Discard all records in the
Abort transfer.
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) .

2
3

3.8

= 5.

Acknowledge Message

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

I ACKNOWLEDGE
where:
ACKNOWLEDGE:

3.9

The OPERATOR field with TYPE

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

CMPFUNC(l)

The access completion functiohs are:
Value

Meaning

Close. Terminate access. Close a file
is
currently
open.
When multiple
streams are in use, close all of
($CLOSE) .

Response. Sent by the accessed process in
response to all Access Complete messages from
the accessing prOcess unless an error occurs.

Purge. Purge a file.
That is, close
delete ($CLOSE + $ERASE) the file.

End-of-stream.
Terminate the data stream
associated with this STREAMID number, but do
not close the file ($OISCONNECT).

Skip. Close the file currently associated
with
this
link
(forcefully,
if
necessary--ignore any errors that may occur
in closing the file) and go on to process the
next file. This function is for use with a
series of wildcard transfers.

that
data
them

and

NOTE
FAL's written to OAP version 4.1
will not return an Access Complete
(Response) to an Access Complete
(End-of-Stream)
(EOS).
FAL's
written to later versions of OAP
will return an Access Complete
(Response). The Access Complete
(End-of-Stream) does not close the
file. The accessed process should
be in a state wherein it can
accept another Control
(Connect)
to open another stream.
FOP(EX-6)

The file access options a user requires.
Refer to
Section 3.4 for option values.
If any portion of the
FOP field in the Access Complete is present, the
whole FOP from the Attributes is superseded with
unspecified bits being set 0.

CHECK(2)

The 16 bit file checksum if requested in the ACCOPT
field of the Access message.
See Section 5.5.2.
Send the checksum only in the Access Complete (Close)
message.
Return a Status message if the checksum is
incorrect. When this field is present, the accessed
process compares the checksums.
If this field is
absent, make no checksum comparison and close the
file even if it is known to contain errors.

3.10

Data Message

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

link.

The

Data

DATA I RECNUM IFILEDATA I
where:
DATA :

The OPERATOR field with TYPE

RECNUM(I-S)

FILEDATA

3.11

= S.

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.
The file data being
totally transparent
byte.

transferred.
This field
is
and uses all S-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:
STATUS

STSCODE

RFA

RECNUM I STV

where:
STATUS

The OPERATOR field with TYPE

STSCODE

A 2-byte status field

= 9.

(16 bits)

subdivided as:

12 11

MACCODE

MICCODE

where:

RFA(I-S)

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(I-8)

STV{I-8)

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.
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)

Name

Meaning

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.

3
4

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 c·orrect.

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) •

Sync

DAP
message
synchronization.

with

received

13-15

Reserved.

16-17

User defined STATUS MACCODES

file

terminating
Format

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

00 00
00 10

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

Configuration
Message
errors by field

01 00

Unknown field.

01 10
01 11

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

01 12
01 13
01 14
01
01
01
01
01
01

20
21
22
23
24
25

01 30

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

02 00

Unknown field.

02 10
02 11

01 26
01 27

Attributes
Message
errors by field

field

02
02
02
02

12
13
14
15

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).

02
02
02
02
02
02
02
02
02
02
02

20
21
22
23
24
25
26
27
30
31
32

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

field

(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)

02 43
02 44
02 45

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).

03 00

Unknown field.

03 10
03 11

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

02
02
02
02
02
02

33
34
35
36
37
40

02 41
02 42

Access
Message
errors by field

Control
Message
errors by field

Reason

03
03
03
03

12
13
14
15

03
03
03
03
03
03

20
21
22
23
24
25

field

03 26

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

04 00

Unknown field.

04 10
04 11

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

04
04
04
04

12
13
14
15

04
04
04
04
04
04
04

20
21
22
23
24
25
26

04 27

field

Control function field (CTLFUNC).
Control menu field (CTLMENU).
Record access field (RAC).
Key field (KEY).
Key of reference field (KRF).
Record options field (ROP).
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)
05 00

Unknown field.

05 10
05 11

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

05 12
05 13
05 14
05 15

Acknowledge
Message
errors by field

05 20

transfer
Continue
(CONFUNC) .

06 00

Unknown field.

06 10
06 11

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

06
06
06
06
Access Complete
Message
errors by field

12
13
14

function

07 00

Unknown field.

07 10
07 11

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

07
07
07
07

12
13
14

07 21
07 22

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

10 00

Unknown field.

10 10
10 11
10 12
10 13
10 14
10 15

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

10 20
10 21

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

07 20

Data Message
errors by field

Reason

field

(continued on next page)

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

Type of Error

(Octal)

Status Message
errors by field

11 00

Unknown field.

11 10
1111
11 12
1113
1114
11 15

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

11
11
11
11
11

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:

20
21
22
23
24

Reason

12 00

Unknown field.

12 10
12 11

field

12
12
12
12

12
13
14
15

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

12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12

20
21
22
23
24
25
26
27
30
31
32
33
34
35
36
37
40
41
42
43
44
45

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 (PaS).
Key segment size field (SIZ).
Key of reference field (REF).
Key name field (KNM).
Null key character field (NUL).
Index area number field (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).

field

(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)
13 00

Unknown field.

13 10
1311

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

13 12
1313
1314
13 15
13
13
13
13
13
13
13
13
13
13

Summary
Messaqe
errors by field

20
21
22
23
24
25
26
27

30
31

Unknown field.

14 10

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

14 12
1413
14 14

14 15
14 20
14 21
14 22
14 23
14 24

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).

14 00
1411

Date and Time
Message
errors by field

Reason

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

field

15 12
15 13
15 14
15 15

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).

15 20
15 21
15 22
15 23
15 24

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

15 00
15 10
15 11

field

(continued on next page)

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

Type of Error

Code
(Octal)

Protection
Message
errors by field

16 00
16 10
16 11

Name Message
errors by field

16
16
16
16

12
13

16
16
16
16
16
16

20
21
22
23
24

17 00
17 10
1711
17
17
17
17

Access Control
List Message
errors by field:
(Reserved for
future use)

12
13
14
15

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

17 20
17 21

Name type field (NAMETYPE).
Name field (NAMESPEC).

20 00

Unknown field.

20 10
20 11

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

20
20
20
20

12
13
14

20 20
20 21

field

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

Table 4
MICCODE Field Values for Use with MAC CODE
Values of 0, 1, 4, 5, 6, and 7 Octal
Value
(Octal)

Error/Reason

NOTE
MICCODE Format: Bits 0-11 contain the error code
number.
Symbolic status codes, where supplied,
refer to the corresponding RMS status codes.
These
codes are included here for ease of
reference only. They have no meaning for DAP.
0
1
2
3
4
5
6
7

15
16
17
20
21
22
23
24

ER$ABO;
ER$ACC;
ER$ACT;
ER$AID;
ER$ALN;
ER$ALQ;
ER$ANI;
ER$AOP;
ER$AST;
ER$ATR;
ER$ATW;
ER$BKS;
ER$BKZi
ER$BLN;
ER$BOF;
ER$BPA;
ER$BPS;
ER$BUG;
ER$CCR;
ER$CHG;

25
26
27
30
31

ER$CHK;
ER$CLS;
ER$COD;
ER$CRE;
ER$CUR;

32
33
34
35
36
37
40
41
42
43
44
45
46
47
50
51

ER$DAC;
ER$DAN;
ER$DEL;
ER$DEV;
ER$DIR;
ER$DME;
ER$DNF;
ER$DNR;
ER$DPE;
ER$DTP;
ER$DUP;
ER$ENT;
ER$ENV;
ER$EOF;
ER$ESS;
ER$EXP;

10
11

12
13
14

Unspecified error.
Operation aborted.
Fll-ACP could not access file.
FILE activity precludes operation.
Bad area ID.
Alignment options error.
Allocation quantity too large or 0 value.
Not ANSI D format.
Allocation options error.
Invalid (i.e., synch) operation at AST level.
Attribute read error.
Attribute write error.
Bucket size too large.
Bucket size too large.
BLN length error.
Beginning of file detected.
Private pool address.
Private pool size.
Internal RMS error condition detected.
Cannot connect RAB.
$UPDATE changed a key without having attribute of
XB$CHG set.
Bucket format check-byte failure.
RSTS/E close function failed.
Invalid or unsupported COD field.
Fll-ACP could not create file (STV=sys err code).
No current record (operation not preceded by
GET/FIND) •
FIl-ACP deaccess error during CLOSE.
Data AREA number invalid.
RFA-Accessed record was deleted.
Bad device, or inappropriate device type.
Error in directory name.
Dynamic memory exhausted.
Directory not found.
Device not ready.
Device .has positioning error.
DTP field invalid.
Duplicate key detected, XB$DUP not set.
RSX-FllACP enter function failed.
Operation not selected in ORG$ macro.
End-of-file.
Expanded string area too short.
File ~xpiration date not yet reached.
(continued on next page)

Table 4
(Cont.)
MICCODE Field Values for Use with MACCODE
Values of 0, 1, 4, 5, 6, and 7 Octal
Value
(Octal)

Error/Reason

52
53
54

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-FIIACP FIND function failed.
ER$FNF; File not found.
ER$FNMi Error in file name.
ER$FOPi Invalid file options.
ER$FULi DEVICE/FILE full.
ER$IANi Index AREA number invalid.
ER$IFI; Invalid IFI value or unopened file.
ER$IMXi Maximum NUM(254) areas/key XABS exceeded.
ER$INI; $INIT macro never issued.
ER$IOP; Operation
illegal
or
invalid
for
file
organization.
ER$IRCi Illegal record encountered (with sequential files
only) .
ER$ISIi Invalid lSI value, on unconnected RAB.
ER$KBFi Bad KEY buffer address (KBF=0).
ER$KEYi Invalid KEY field (KEY=0/neg).
ER$KRFi Invalid key~of-reference ($GET/$FIND).
ER$KSZi KEY size too large.
ER$LANi Lowest-level-index AREA number invalid.
ER$LBLi Not ANSI labeled tape.
ER$LBYi Logical channel busy.
ER$LCHi Logical channel number too large.
ER$LEXi Logical extend error, prior extend still valid.
ER$LOCi LOC field invalid.
ER$MAPi Buffer mapping error.
ER$MKDi FII-ACP could not mark file for deletion.
ER$MRNi MRN value=neg or relative key>MRN.
ER$MRSi MRS value=0 for fixed length records. Also 0 for
relative files.
ER$NAMi NAM block address invalid
(NAM=0,
or
not
accessible) .
ER$NEFi Not positioned to EOF (sequential files only) .
ER$NIDi Cannot allocate internal index descriptor.
ER$NPKi Indexed filei nO primary key defined.
ER$OPNi RSTS/E open fUnction failed.
ER$ORDi XAB'S not in correct order.
ER$ORGi Invalid file organization value.
ER$PLGi Error in file's prologue (reconstruct file).
ER$POSi POS field invalid (POS>MRS,STV=XAB indicator).
ER$PRMi Bad file date field retrieved.
ER$PRVi Privilege violation (OS denies access) .
ER$RABi Not a valid RAB (BID NOT=RB$BID) .
ER$RACi Illegal RAC value.
ER$RATi Illegal record attributes.

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
III
112
113
114
115
116
117
120
121
122
123
124
125
126
127
130

(continued on next page)

Table 4
(Cont.)
MICCODE Field Values for Use with MAC CODE
Values of 0, 1, 4, 5, 6, and 7 Octal
Value
(Octal)

Error/Reason

131

ER$RBF; Invalid record buffer address
(ODD, or
not
word-aligned if BLK-IO) .
ER$RER; File read error.
ER$REX; Record already exists.
ER$RFA; Bad RFA value (RFA=0).
ER$RFM; Invalid record format.
ER$RLK; Target bucket locked by another stream.
ER$RMV; RSX-Fll ACP remove function failed.
ER$RNF; Record not found.
ER$RNL; Record not locked.
ER$ROP; Invalid record options.
ER$RPL; Error while reading prologue.
ER$RRV; Invalid RRV record encountered.
ER$RSA; RAB stream currently active.
ER$RSZ; Bad record size (RSZ>MRS, or NOT=MRS if fixed
length records).
ER$RTB; Record too big for user s buffer.
ER$SEQ; Primary key out of sequence
(RAC=RB$SEQ for
$PUT) .
ER$SHR; SHR field invalid for
file
(cannot
share
sequential files).
ER$SIZ; SIZ field invalid.
ER$STK; Stack too big for save area.
ER$SYS; System directive error.
ER$TRE; Index tree error.
ER$TYP; Error in file type extension on FNS too big.
ER$UBF; Invalid user buffer addr (0, ODD, or if BLK-IO
not word aligned).
ER$USZ; Invalid user buffer size (USZ=0).
ER$VER; Error in version number.
ER$VOL; Invalid volume number.
ER$WER; File write error (STV=sys err code).
ER$WLK; Device is write locked.
ER$WPL; Error while writing prologue.
ER$XAB; Not a valid XAB (@XAB=ODD,STV=XAB indicator).
BUGDDI; Default directory invalid.
CAA
; Cannot access argument list.
CCF
; Cannot close file.
CDA
; Cannot deliver AST.
CHN
; Channel assignment failure (STV=sys err code).
CNTRLO; Terminal output ignored due to (CNTRL) o.
CNTRLY; Terminal input aborted due to (CNTRL) Y.
DNA
; Default filename string address error.
DVI
; Invalid device 1.0. field.
ESA
; Expanded string address error.
FNA
; Filename string address error.
FSZ
; FSZ field invalid.
IAL
; Invalid argument list.
KFF
; Known file found.
LNE
; Logical name error.
NOD
; Node name error.
NORMAL; Operation successful.
OK_DUP; Record inserted had duplicate key.

132
133
134
135
136
137
140
141
142
143
144
145
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

(continued on next page)

Table 4 ,(Cont.)
MICCODE Field Values for Use with MAC CODE
Values~f 0, 1, 4, 5, 6 and 7 Octal
Value
(Octal)

Error/Reason

211
212
213

OK IDX: Index update error occurred-record inserted.
OK-RLK: Record locked but read anyway.
OK:=RRV: Record inserted in primary o.k.: may not be
accessible by secondary keys or RFA.
CREATE~ File was created, but not opened.
PBF
: Bad prompt buffer address.
PNDING: Async. operation pending completion.
QUO
: Quoted string error.
RHB
: Record header buffer invalid.
RLF
: Invalid related file.
RSS
: Invalid resultant string size.
RST
: Invalid resultant string address.
SQO
: Operation not sequential.
SUC
: Operation successful.
SPRSED: Created fil~ superseded existing version.
SYN
: Filename syntax error.
TMO
: Time-out period expired.
ER$BLK: FB$BLK record attribute not supported.
ER$BSZ: Bad byte size.
ER$CDR: Cannot disconnect RAB.
ER$CGJ: Cannot get JFN for file.
ER$COF: Cannot open file.
ER$JFN: Bad JFN value.
ER$PEF: Cannot position to end-of-file.
ER$TRU: Cannot truncate file.
ER$UDF; File is currently in an undefined state; access
is denied.
ER$XCL; File must be opened for exclusive access.
; Directory full.
; Handler not in system.
; Fatal hardware error'.
; Attempt to write beyond EOF.
; Hardware option not present.
; Devite not attached.
: Device already attached~
: Device not attachable.
: Sharable resource in use.
; Illegal overlay request.
: Block check or CRC e~ror.
: Caller s nodes exhausted.
: Index file full.
; File header full.
; Accessed for write.
: File header checksum failure.
; Attribute control list error.
: File already accessed on LUN.
: Bad tape format.
: Illegal operation an file descriptor block.
; Rename; 2 different devices.
; Rename; new filename already in use.
; Cannot rename old file system.
; File already open.
: Parity error on device.

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
253
254
255
256
257
260
261
262
263
264
265
266
267
270
271
272
273

(continued on next page)

Table 4 (Cont.)
MICCODE Field Values for Use with MACCODE
Values of 0, 1, 4, 5, 6, and 7 Octal
Value
(Octal)
274
275
276

277
300
301
302
303
304
305
306
307
310

311
312
313
314
315
316
317
320
321
322
323
324
325
326
327
330
331
332
333
334
335
336
337
340
341
342
343
344
345
346
347
350

Error/Reason

;

End of volume detected.

·; Bad block on device.
, Data over-run.

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.
SPL
; Spool or submit command file failure.
NMF
; No more files.
CRC
; DAP file transfer checksum error.
; Quota exceeded
BUGDAP; Internal network error condition detected.
CNTRLC; Terminal input aborted due to (CNTRL) C.
, Data bucket fill size > bucket size in XAB.
DFL
ESL
; Invalid expanded string length.
IBF
; Illegal bucket format.
IBK
; Bucket size of LAN NOT = IAN in XAB.
IDX
; Index not initialized.
IFA
; Illegal file attributes (corrupt file header).
IFL
; Index bucket fill size > bucket size in XAB.
KNM
; Key name buffer not readable or writeable in XAB.
KSI
; Index bucket will not hold two keys
for key of
reference.
MBC
; Multi-buffer count invalid (negative value).
NET
; Network operation failed at remote node.
OK - ALK; Record is already locked.
OK - DEL; Deleted record successfully accessed.
OK - LIM; Retrieved record exceeds specified key value.
OK- NOP; Key XAB not filled in.
OK RNF; Nonexistent record successfully accessed.
PLV
; Unsupported prologue version.
REF
; Illegal key-of-reference in XAB.
RSL
; Invalid resultant string length.
RVU
; Error updating rrv's, some paths to data
may be
lost.
SEG
; Data types
other than string limited to one
segment in XAB.
, Reserved
SUP
; Operation not supported over network.
, Error on write behind.
WBE
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.
listing--error
in
reading
file
; Directory
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 for Use with MACCODE
Values of 0, 1, 4, 5, 6, and 7 Octal
Value
(Octal)

Error/Reason

351
352
353
354
355
356
357

SNE
SPE
UPI
ACS

360
361
362
363
364
365

TNS
BES
PES
WCC
IDR
STR

366

FTM

6000
to
7777

; Directory listing--protection violation in trying
to read file attributes.
; Directory listing--file attributes do not exist.
; Directory listing--unable to recover directory
list after Continue Transfer (Skip).
; Sharing not enabled.
; Sharing page count exceeded.
; UPI bit not set when sharing with BRO set.
; Error in access control strihg (poor man's route
through error).
; Terminator not seen.
; Bad escape sequence.
; Partial escape sequence.
; Invalid wildcard context val ue.
; Invalid directory rename operation.
; User structure (FAB/RAB) became invalid dur ing
operation.
; Network file transfer mode precludes operation.
; User defined errors

Table 5
MICCODE Field Values
(with MACCODE Value of 12 Octal)
Value
(Octal)

Error/Reason
NOTE
MICCODE Formatl
type number.

o
1
2

3
4

5
6
7

10
11

12
13
14
15
16
17
20

Bits 0-11

contain

the

message

Unknown message type
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
Date and Time Attributes Extension message
Protection Attributes Extension message
Name message
Access Control List Extended Attributes message
44

3.12

Key Definition Attributes Extension Message

Each key is defined by a group of 19 fields.
definition message is:

The

form

, KEYDEF' KEYMENU' FLG' DFL' IFL' NSG' POS' SIZ' [POS, SIZ .•. ]' REF' KNM

KEYDEF :

the

key

The operator field with TYPE = 10.

KEYMENU (EX-6)

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 be in the order
specified.
Bit

Meaning (When Set)

0
1
2
3
4
5
6
7
8
9
10

FLG
DFL
IFL
NSG, POS and SIZ
REF
KNM
NUL
IAN
LAN
DAN
DTP
RVB
HAL (reserved)
DVB
DBS
IBS
LVL
TKS
MRL

12
13

14
15
16
17
18
FLG (EX-3)

Key option flag
bit 0
bit 1
bit 2

XB$DUP duplicates allowed
XB$CHG allow keys to change
XB$NUL null key character defined

DFL (2)

Data bucket fill.

IFL (2)

Index bucket fill.

NSG(l)

Number of segments (max. 8) needed to define the
key in the record. For each segment, there will
be a POS, SIZ pair.
For example, if NSG
contains 3, the following sequence of fields
would appear:

POS(2)

position of key in record by byte number.
first byte in the record is byte 0.

SIZ(l)

Size of key in record in bytes.

REF(l)

Key Of reference indicator.

The

KNM(I-40) :A

Key name correspoding to key of reference
above.

NUL (1)

Value of null key character.

IAN (1)

Index area number.

LAN (1)

Lowest level index area number.

DAN (1)

Data level area number.

DTP (1)

Data type.

(REF)

RVB (1-8)

Root VBN for key.

HAL(I-5)

Hash algorithm value (reserved).

DVB(I-8)

First data bucket start virtual block number.

DBS (1)

Data bucket size field.

IBS(l)

Index bucket size field.

LVL(l)

Level of root bucket.

TKS(l)

Total key size.

MRL (2)

Minimum record length~
the minimum
record
length in bytes which will totally contain the
key field for the key described by this message.

3.13

Allocation Attributes Extension Message

Use the Allocation message when creating .or explicitly extending a
file to specify the character of the allocation. The form of the
allocation message is:

ALLOC

The operator field with TYPE = 11.

ALLMENU (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.
They must be in the order
specified.
Bit
0

1
2

3
4

5
6
7
8

VOL (2)

Meaning (When Set)
VOL
ALN
AOP
LOC
RFI
ALQ
AID
BKZ
DEQ

(reserved)

Relative volume number of a volume set on
this area or file will be allocated.

which

ALN(EX-4)

AOP (EX-4)

LOC (1-8)

Alignment options
Bit

Meaning

Explanation

XB$ANY

XB$CYL
XB$LBN

XB$VBN

XB$RFI

No
specified
allocation
placement.
Align on cylinder boundary.
Align
to
specified
logical
block.
Allocate as near as possible to
specified virtual block.
Allocate as near as possible
to
specified related file.

Allocation options
Bit

Meaning

Explanation

XB$HRD

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:

If ALN

XB$CYL, LOC
is the cylinder
number
where allocation is to start.
If ALN
XB$LBN, LOC is the logical block where
allocation is to start.
If ALN
XB$VBN, LOC is the virtual block near
which allocation should start;
o (default) means as near as
possible to current EOF.
If ALN = XB$RFI, LOC is a VBN but a VBN
in the
related file.
RFI ( I -l6 )

: B

Related file 1.0.

ALQ (1-5)

: B

The amount of space
in virtual blocks to be
allocated.
Returns actual size of allocation.
For DISPLAY, returns size of area.

AID (1)

Area 1.0. The area number used to
identify
area for reference by a key definition.

BKZ (1)

Bucket size for this area.

DEQ( 2)

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.

(reserved) .

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:
I SUMMARyISUMENU!NOKINOAINORlpVN
where:
The operator field with TYPE = 12.

SUMMARY
SUMENU (EX- 6)

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
(!J

2
3

Meaning (When Set)
NOK
NOA
NOR
PVN

NOK{l)

Number of keys defined in file.

NOA{l)

Number of areas defined in file.

NOR (I)

Number of record descriptors in file.

PVN (2)

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:

IDATIMEI DATMENUICDTIRDTIEDT IRVN
where:
OATIME
OATMENU (EX-6)

The operator field with TYPE = 13.
8M

The following bit map specifies which of th~
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
3

Meaning (When Set)
COT
ROT
EDT
RVN

CDT(18)

Date and time file created in
Time (NST).

RDT(18)

Date and time file last updated in NST.

Date and time file may be deleted in NST.

EDT(18)

The preceding three
following format:

fields

Network

should

Standard

the

dd-mon-yybhh:mm:ss
where:
dd is the day
mon is a three letter abbreviation for the month
as follows:
JAN
FEB
MAR
APR
MAY
JUN
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
RVN(2)

: B

Revision number--the number 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), GMT 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:
[PROTECTlpROTMENUloWNERlpROTSYS!PROTOWNfpROTGRPlpROTWLD

where:
The OPERATOR field with TYPE

PROTECT
PROTMENU(EX-6)

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
0
1

2
3
4

OWNER (1-40)

PROTSYS(EX-3)

= 14.

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.
BM

File protection for system access rights.
Bit

Meaning (When Set)

0
1
2

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.

3
4

5
6
7
S

PROTOWN(EX-3)

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

PROTGRP(EX-3)

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

PROTWLD (EX- 3)

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!NAMETYPEINAMESPEC
where:
NAME:

The operator field with TYPE

NAMETYPE (EX- 3)

= 15.

Type of name contained in NAMESPEC field.
Bit

Meaning
File specification
File name
Directory name
Volume or structure name
Default file specification
( reserved)
Related file specification
(reserved)

0
1
2
3
4
5

NOTE
Here the file specification means the
full
file specification including the
volume, directory, and file name.
NAMESPEC(I-200)

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

format
field

3.1B 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 .•. J
ACLTYPE :

The operator field with TYPE

= 16.

ACLCNT(l)

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(I-B0)

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.
51

4.0

FILE ORGANIZATION

4.1

Types of Files

The following types of files are addressed by this specification:

4.2

•

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.

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)
(DLE)
(DCl)
(DC2)
(DC3)
(DC4)
(VT)
(LF)
(ESC)
(AZ)

in the
used to

Form feed
Data link escape

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:
1.

FORTRAN carriage control

COBOL carriage control

Print file carriage control

Implied LF/CR envelope for printing

Embedded carriage control

Line sequential ASCII

MACYll

None of the above

4.2.1 Handling Stream ASCII ~- Stream ASCII files consist of a string
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.

4.2.2 Conversions -- DAP does not specify data or format 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) •

4.3.2 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.

4.3.3 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 Stream - Here a file contains just a stream of ASCII
characters with no real concept of records.
However, delimiters are
used to terminate "records" for purposes of reading and writing the
file.

4.4

Supported Data Types

The DATATYPE field of the Attributes message
representation used to transfer data. These are:

defines

the

code

ASCII
Image
EBCDIC (Reserved)
In addition, there is a COMPRESSION option mode, which can be used
with any of the above.
This compressed mode reduces the amount of
data sent by encoding blanks and duplicates.

4.4.1 ASCII - This is the 7-bit ASCII code-set as defined in the 1968
ANSI standard.
To transmit this within 8-bit frames, the high order
bit is ignored except when using 7-bit compression. On card readers,
this refers to the ASCII encoding of the punches into the 128
character codes.

4.4.2

EBCDIC - this is an IBM 8-bit EBCDIC code set.

(Reserved)

4.4.3 Image - This is a mode for transmitting data in DAP where no
code set is specified and data records (or blocks) are simply regarded
as ordered strings of bits.
The number of bits in a bit string (image
mode record) need not be a multiple of 8 although the bit strings are
in fact transmitted in 8-bit frames
(a requirement of lower level
protocols) .
When transmitting Image data, if the number of data bits in the
message is not a multiple of 8 (the number of actual data bits in a
DAP Data message must be a multiple of the byte size as specified by
BSZ
in the Attributes message), the field BITCNT in the header of the
Data message must be used.
The BITCNT field specifies the number of
bits in the final 8-bit frame of the Data message which are not actual
data bits.
The non-data bits are padding bits required to fill
out
the 8-bit frame.
When transferring bit strings where the bit count is a multiple of
it is not necessary to use BITCNT.

The order in the bit strings is low order bit of low order byte first,
second bit of low byte, and so on, followed by the same sequence for
successively higher order bytes. For example, consider retrieving the
3 byte record with 6-bit bytes shown below. The order of the string
is as shown below with the first bit on the right and the last bit in
the string on the left (the top row of single digit numbers inside the
boxes is byte numbers and the bottom row is bit numbers. Thus for any
bit position in the string, the top digit gives the byte and the
bottom digit the bit within that byte).
byte 2

byte 1

byte 0

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

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

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

In Image record mode, this string transmits in 3 8-bit frames in a DAP
Data message as follows:
frame 2

frame 1

frame 0

x x x x x x 2 2
5 4

2 2 221 1 1 1
3 21054 3 2

1 10000 0 0
1 05432 1 0

with frame 0 being transmitted first, low order bit first.
are padding. BITCNT is 6 for this DAP Data message.

The

x's

If this image record is being sent to a system which
7-bit bytes, this record is stored as follows:

data

byte 2

byte 1

byte 0

x x x 222 2
543 2

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

1 0 000 0 0
0 5 43 2 1 0

stores

4.4.4 Compression - Any of the encodings, even the Image mode, may be
compressed on transmission to eliminate the sending of duplicates and
multiple blanks. The compression technique is slightly different with
7-bit and 8-bit character encodings.
7-bit compression:

Send non-compressed characters with high order bit
low 7-bits = character:
(0) (7-bit char).

Send blanks as high bits = 10 followed by number of blanks in
6-bit binary:
(10) (number blanks).

Send repetitions as high bits = 110 followed by number of
repetitions in 5-bit binary:
(110) (number reps) followed by
the repeated character.

An escape scheme allows sending of l2-bit card images when
they do not encode into the ASCII code set by sending high
bits = 1111 followed by columns 12-1 and another character of
columns 2-9.
For example, send (1111) (12,11,0,1) in the
first character and
(2,3,4,5,6,7,8,9)
in
the
second
character.

and

The high bit sequence
expansion.

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

Summary 7-bit compression:
0xxxxxxx
10xxxxxx
110xxxxx
llllxxxx
xxxxxxxx
1110xxxx

1110

has

been

reserved

for

future

may

7-bit non-compressed characters
number of blanks (the character octal 40)
number of repeated characters
12-bit card image
12-bit card image (continued)
reserved

a-bit compression:
with a-bit codes the blanks, repetitions and 12-bit card image are the
same as the 7-bit case. Precede a-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" a-bit characters. Following
this may be another string, blanks or repetitions.
Summary:
0xxxxxxx
10xxxxxx
110xxxxx
1110xxxx
llllxxxx
xxxxxxxx

number of non-compressed characters
number 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

OAP transfers data to and from I/O devices and mass storage files
independent of the I/O structure of the system being accessed. This
transfer is accomplished by communication with a OAP process that
accepts OAP requests on the network side and translates them into
equivalent requests to the local I/O system.
From the network it
appears as if OECnet systems support OAP messages directly within
their file systems.
OAP 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 OAP protocol operate at the application
level within a OECnet 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 OAP environment.
Once the link is
established, the processes may exchange OAP 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) OAP process to the accessed
(server) OAP process.
Following link establishment, the OAP-speaking processes
Configuration messages. The purposes of this exchange are:
l.

To establish the maximum buffer
level protocol messages

To identify system type to each other

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

To inform the opposite process of the generic capabil i ties of
the system sending the message

size

for

exchange

exchanging

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 OAP processes the generic capabilities of the other OAP 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 the file or device resides is the accessed node while
the node where the user process is located is the accessing node. The
accessing process initiates the connection. For each DAP message sent
over the link, a transmit request and corresponding receive request
must be issued to Session Control
(DNA Session Control Functional
Specification) .
This document explains the DAP messages only and
assumes that the necessary receives and transmits are issued by the
processes involved.
After link creation and the exchange of Configuration messages, the
accessing process sends an Attributes message, optionally followed by
one or more Extended Attributes messages, specifying the mode and
format of the data and the structure of the file. This is then
followed by an Access message specifying the desired operation.
The
Access message may be preceded by a Name message if the default
filename option is required.
The Attributes, Extended Attributes,
Name, and Access messages may be blocked and sent together in one
transmission if buffer space is available (the LENGTH field must be
used)
and if blocking is supported as indicated by the Configuration
message. Alternately, if a DAP message is too long to be sent as .a
single
entity
due to limitations of the underlying Transport
mechanism, the DAP message may be segmented and sent in two or more
pieces
(see FLAGS field in message header)
if segmentation is
supported.
Systems not retaining the file attributes use the Attributes message
to set the attributes for the transfer. When creating a new file, the
Attributes message sent by the accessing process specifies the
attributes the new file should have.
If the accessed system does not
support these attributes, it returns a Status message to that effect.
When storing records with systems retaining attributes, the accessing
system uses the Attributes message returned by the accessed system to
indicate the attributes the records being sent should have.
For
record retrieval with systems retaining attributes,
records are
transferred with the attributes of the Attributes messages returned by
the accessed process.
After the initial set up messages are sent, the accessing system
receives a response from the accessed process.
If the access
specified opens a file, an Attributes message and Extended Attributes
messages followed by an Acknowledge message is sent from the accessed
system containing the actual attributes of the accessed file.
If the
operation specified in the Access message deletes, renames or executes
a file, no Attributes messages or Acknowledge messages are returned
and the response is an Access Complete message.
To minimize the tying up of network resources (such as logical links
and buffers), the Configuration, Attributes, Extended Attributes,
Name, and Access messages should be sent in a timely manner. A timer
may be set for each message and if it does not arrive in a reasonable
time the link may be disconnected by the accessed process. After the
Acknowledge message has been received, the file is open and the
accessing process sets the pace for access of the file.
If there are errors in the setup procedure, a Status message
returned.
NOTE
A receive must always be outstanding in
order
to
accept both expected and
unexpected DAP Status messages.
Status
messages are always sent as ordinary
(not Interrupt) messages.
59

will

If an error is detected in a Status message, either during or after
setup, a protocol error has occurred and there is nothing that can be
done to recover so the link should be disconnected.
Errors in exchanging Configuration messages should be very rare since
the information in Configuration messages will generally be "canned"
and of an informative nature. If the accessed system detects an error
in the Configuration message, it returns a Status message and the
accessing system can either retry or disconnect.
If the accessing
system detects an error, it disconnects.
NOTE
If, however, a Configuration message
appears to be in error because the
SYSCAP field is too long and the DAP
version number is greater than that to
which the current software is written,
assume that the SYSCAP field has been
extended in the later version of DAP.
Ignore this error.
This is the only
time when an error is ignored.
The
assumption
is
that
the
more
sophisticated DAP process uses only a
subset of the protocol and thus both
sets of software can work together.

5.1.1 Errors in the Setup Sequence - The accessed process returns a
Status message for errors detected in each message (Configuration,
Attributes, Name, and Access). On receiving an error in response to
one of these messages, there are three possibilities open to the
accessing DAP process:
1.

Disconnect the link.

Send the corrected message responsible for the error.
There
is no point in sending the original message unless there is
sufficient doubt that the message was delivered properly or
that the error indicated was of a temporary nature. For
example, an attempt was made to open a file already open by
another ~rocess.

Start a different access. A new access usually starts with
an Attributes message, but it could start with an Access
message (where the type of access does not require attributes
such as ERASE) or even a Configuration message.

If the user process tries to recover by sending a corrected message or
starting a new access, the accessed DAP process can accept any of the
setup messages in response to a Status message. Table 6 contains a
list of responses to setup message errors. In this table, Extended
Attributes messages are considered as being Attributes messages and
Name messages part of the Access message. When recovering from an
error in an Attributes Extension message, the accessing process should
back up to the Attributes message.

Table 6
Responses to Setup Message Errors
..

Responses
Error

Configuration
Message

Attributes
Message

Access
Message

Configuration Message

Attributes Message

Access Message

where:
0
1
2

Invalid response.
Valid response.
Valid response only
attributes message.

for

accesses

requiring

Errors detected by the accessing process in Attributes, Extended
Attributes,
Name and Acknowledge messages cause the accessing process
to disconnect the logical link thus terminating the access.

5.1.2 Setup Sequence - If a timer is used between setup messages,
this same timer should be set by the accessed process after an error
during setup.
If the timer expires, a disconnect should be initiated.
The following conventions are used in DAP message sequence diagrams in
this and subsequent sections:
•

Brackets [ 1 denote optional messages.

•

Messages on the left side of the arrows are from the accessing
process.

•

Messages on the right side
accessed process.

the

arrow

are

NOTE
The message sequence diagrams in this
and
subsequent
sections
are
not
definitive. However, although they do
not cover every situation that can arise
with DAP remote file access, they should
be complete enough to give an idea of
what should be done in those situation~
not explicitly addressed.

sent

the

After a logical link is established, the setup sequence is as 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:
ATTRIBUTES------)
[EXTENDED
ATTRIBUTES]----)
[NAME-----------)
(DEFAULT)]
ACCESS-----~----)

<------ATTRIBUTES
[EXTENDED
<------ATTRIBUTES]
<------[NAME (EXPANDED FILESPEC)]
<------ACKNOWLEDGE

NOTES

An
Attributes
message
is
not
required when the Access message
specifies ERASE, RENAME, DIRECTORY
LIST, or EXECUTE command file.
For
these types of access, the accessed
process
returns
neither
the
Attributes
message
nor
the
Acknowledge
message
unless
specifically
requested
by
the
DISPLAY field.
If the DISPLAY field
is omitted from the Access message
and the function is OPEN, CREATE, or
SUBMIT, the accessed process returns
a Main Attributes message. When a
DISPLAY field is present in
an
Access message, the accessed process
returns only the messages requested
by the DISPLAY field. When RENAME
is specified, follow the
Access
message by a Name message containing
the new name for the file
(see
Section 5.2.8).

Request the optional Name message
returned by the accessed process
after opening the file by setting a
bit in the DISPLAY field of the
Access message.
The Name message
contains the file specification of
the file opened or created after all
the logical names have been resolved
and defaults applied.

Error in Configuration messages:
(a)

Disconnect after error detected:
CONFIGURATION------>(error detected)
<------STATUS
DISCONNECT
or

(b)

Correcting erroneous message:
CONFIGURATION----~->(error

detected)

<------STATUS
CONFIGURATION------>
or
(c)

If the error is in the returned message:
CONFIGURATION------>
(in error)

<------CONFIGURATION

DISCONNECT
63

Error in Attributes message:
(a)

Disconnect after erroneous message:
ATTRIBUTES-----~>(error

detected)

<------STATUS
DISCONNECT
or
(b)

Correcting erroneous message:
ATTRIBUTES~----->(error

detected)

<------STATUS
ATTRIBUTES------>
or
(c)
Starting anew 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
ACCESS
5.

...,----->

Error in Optional Extended Attributes message:
(a)

Disconnect after erroneous message:
ATTRIBUTES------>
EXTENDED
ATTRIBUTES 1----->

EXTENDED
ATTRIBUTES n----->(error detected)
<------STATOS
DISCONNECT
or

(b)
Correcting erroneous message (note that restart backs up
to the Attributes message) :
ATTRIBUTES------>
EXTENDED
ATTRIBUTES 1----->

EXTENDED
ATTRIBUTES n----->(error detected)
<------STATUS
ATTRIBUTES----->
EXTENDED
ATTRIBUTES 1----->

EXTENDED
ATTRIBUTES n----->

etc.
(c)

Starting new access on same link:
ATTRIBUTES-------->
EXTENDED
ATTRIBUTES 1------>

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

------>

ACCESS
6.

Error in Name message for default file specification:
(a)

Disconnect after erroneous message:
NAME

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

DISCONNECT

(b)

Correcting erroneous message:
NAME