ISO/IEC 13239:1997

ISOAEC
INTERNATIONAL
STANDARD
First edition
1997-06-I 5
Information technology -
Telecommunications and information
exchange between systems - High-level
data link control (HDLC) procedures
TMcommunications et Bchange
Technologies de I’informa tion -
d ‘informa tion en tre sys t&mes - Pro&dures de commande de liaison de
don&es 2 haut niveau (HDLC)
Reference number
ISOAEC 13239: 1997(E)
ISO/IEC 13239: 1997(E)
Contents
Page
iv
Foreword .
V
Introduction .
1 Scope .
............................................................................
2 Normative references
.............................................. 2
3 Definitions, acronyms and abbreviations
3.1 Definitions .
................................................................
3.2 Acronyms and abbreviations
.......................................................................... 8
4 HDLC frame structure
........................................................................... 8
4.1 Elements of the frame
4.2 Transparency .
Transmission considerations .
4.3
..............................................................................
4.4 Inter-frame time fill
........................................................................................ 13
4.5 Invalid frame
4.6 Extensions .
4.7 Addressing conventions .
HDLC elements of procedures .
........................................................................ 14
5.1 Data link channel states
5.2 Modes .
5.3 Control field formats .
5.4 Control field parameters . 19
..................................................................... 22
5.5 Commands and responses
......................................... 41
5.6 Exception condition reporting and recovery
................................................................. 45
6 HDLC classes of procedures
Types of data station . 45
6.1
...................................................................................... 46
6.2 Configurations
................................................................................ 46
6.3 Operational modes
6.4 Addressing scheme . 46
Send and receive state variables . 46
6.5
....................................................... 46
6.6 Fundamental classes of procedures
................................................................................ 47
6.7 Optional functions
.................................................... 48
6.8 Consistency of classes of procedures
6.9 Conformance to the HDLC classes of procedures . 49
Method of indicating classes and optional functions . 49
6.10
........................ 50
6.11 Unbalanced operation (point-to-point and multipoint).
......................................................
6.12 Balanced operation (point-to-point) 53
6.13 Unbalanced connectionless operation (point-to-point and multipoint). . 56
6.14 Balanced connectionless operation (point-to-point) . 58
............................................................... 60
6.15 Uses of the optional functions
0 ISO/IEC 1997
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ii
OISO/IEC
7 General purpose Exchange Identification (XID) frame. . 65
General purpose XID frame information field structure. . 65
7.1
7.2 General purpose XID frame information field encoding. . 65
7.3 Single-frame exchange negotiation process . 69
7.4 Frame check sequence negotiation rules . 71
Resolution/negotiation of data link layer address in switched
environments .
8.1 Operational requirements . 71
8.2 Address resolution . 71
Annexes
A Explanatory notes on the implementation of the frame checking
sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
B Example of the. use of commands and responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Time-out function considerations for NRM, ARM and ABM . . . . . . . . . . . . . . 96
C
D Examples of typical HDLC procedural subsets . . . . . . . . .*. 98
E Illustrative examples of FCS negotiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
F Guidelines for communicating with LAPB X.25 DTEs. . . . . . . . . . . . . . . . . . . . . . 103
Examples of information field encoding in multi-selective reject
G
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
frames 104
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ISO/IEC 13239: 1997(E) 0 ISOAEC
Foreword
IS0 (the International Organization for Standardization) and IEC (the International
Electrotechnical Commission) form the specialized system for worldwide standardization.
National bodies that are members of IS0 or IEC participate in the development of
International Standards through technical committees established by the respective
organizations to deal with particular fields of technical activity. IS0 and IEC technical
committees collaborate in fields of mutual interest. Other international organizations,
governmental and non-governmental, in liaison with IS0 and IEC, also take part in the
work.
In the field of information technology, IS0 and IEC have established a joint technical
committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical
committee are circulated to national bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the national bodies casting a vote.
International Standard ISO/IEC 13239 was prepared by Joint Technical Committee
ISO/IEC JTC 1, Information technology, Subcommittee SC 6, Telecommunications and
information exchange between systems.
Annexes A to G of this International Standard are for information only.
iv
ISO/IEC 13239: 1997(E)
OISOIIEC
Introduction
This International Standard i sa composition of the following HDLC-related International
Standards and Amendments:
ISOAEC 3309: 1993
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - Frame
structure
ISO/IEC 3309: 1993/DAM4
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - Frame
structure -Amendment 4: Optional range of FCS checking
ISO/IEC 4335:1993
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - Elements
of procedures
ISO/IEC 4335:1993/Amd.6:1995
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - Elements
of procedures - Amendment 6: Extension of HDLC sequence number modulus
beyond I28
ISO/IEC 4335:1993Mmd.7:1995
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - Elements
of procedures - Amendment 7: Enhanced multi-selective reject option
ISO/IEC 4335: 1993fDAM8
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - Elements
of procedures - Amendment 8: Unnumbered information frame with header
check (UIH) command and response
ISO/IEC 4335:1993/DAM9
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - Elements
of procedures - Amendment 9: Span list encoding of the information field in the
multi-SREI frame
ISO/IEC 7809: 1993
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - Classes of
procedures
ISO/IEC 13239: 1997(E)
0 ISO/IEC
ISO/IEC 7809: 1993Amd. 10: 1995
Telecommunications and information exchange
Information technology ~
between systems - High-level data link control (HDLC) procedures - Classes
ofprocedures - Amendment 10: Extension of HDLC sequence number modulus
beyond I28
ISO/IEC 7809: 1993/DAM 11
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - Classes
of procedures - Amendment 1 I: Unnumbered information frame with header
check (UIH) command and response
ISO/IEC 7809: 1993/DAM 12
Information technology - Telecommunications and information exchange
High-level data link control (HDLC) procedures - Classes
between systems -
Amendment 12: Span list encoding of the information field in
of procedures -
the multi-SRUframe
ISO/IEC 8885: 1993
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - General
purpose XID frame information field content and format
ISO/IEC 8885: 1993/Amd.9:1995
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - General
purpose XID frame information field content and format - Amendment 9:
Extension of HDLC sequence number modulus beyond 128
ISO/IEC 8885:1993/DAMlO
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - General
purpose XID frame information field content and format - Amendment IO:
Unnumbered information frame with header check (UrH) command and response
ISO/IEC 8885:1993/DAMll
Information technology - Telecommunications and information exchange
between systems - High-level data link control (HDLC) procedures - General
purpose XID frame information field content and format - Amendment II:
Span list encoding of the information field in the multi-SREI frame
ISO/IEC 847 1: 1987
Information processing systems - Data communication - High-level data link
control balanced classes of procedures - Data-link layer address
resolution/negotiation in switched environments

ISO/IEC 13239: 1997(E)
OISOIIEC
High-level data link control (HDLC) procedures are designed to permit synchronous or
start/stop, code-transparent data transmission.
The normal cycle of the code-transparent
data communication between two data stations consists of the transfer of frames
containing information from the data source to the data sink acknowledged by a frame in
the opposite direction. Generally, until the data station comprising the data source
receives an acknowledgement, it holds the original information in memory in case the
need should arise for retransmissions.
In those situations that require it, data sequence integrity between the data source and the
data sink is effected by means of a numbering scheme, which is cyclic within a specified
modulus and measured in terms of frames. An independent numbering scheme is used
for each data source/data sink combination on the data link.
The acknowledgement function is accomplished by the data sink informing the data
source of the next expected sequence number. This can be done in a separate frame, not
containing information, or within the control field of a frame containing information.
HDLC procedures are applicable to unbalanced data links and to balanced data links.
Unbalanced data links
An unbalanced data link involves two or more participating data stations. For control
purposes, one data station on the data link assumes responsibility for the organization of
data flow and for unrecoverable data link level error conditions. The data station
assuming these responsibilities is known as the primary station in unbalanced
connection-mode data links and as the control station in unbalanced connectionless-mode
data links, and the frames it transmits are referred to as command frames. The other data
stations on the data link are known as the secondary stations in unbalanced connection-
mode data links and as the tributary stations in unbalanced connectionless-mode data
links, and the frames they transmit are referred to as response frames.
For the transfer of data between the primary/control station and the secondary/tributary
stations, two cases of data link control are considered (see figures A and B). In the first
case, the data station comprising the data source performs a primary/control station data
link control function and controls the data station comprising the data sink that is
associated with a secondary/tributary station data link control function, by select-type
commands.
In the second case, the data station comprising the data sink performs a primary/control
station data link control function and controls the data station comprising the data source
that is associated with a secondary/tributary station data link control function, by poll-
type commands.
from the data source
The information flows to the data sink, and the acknowledgements
opposite
are always transmitted in the directi .on.
link control may be combined
These two cases of data so that the data link becomes
two-way altern .ate communication, or two-way simultan
capable of .eous communication.
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ISO/IEC 13239: 1997(E) 0 ISO/IEC
Balanced data links
A balanced data link involves only two participating data stations. For control purposes,
each data station assumes responsibility for the organization of its data flow and for
unrecoverable data link level error conditions associated with the transmissions that it
originates. Each data station is known as a combined station in balanced connection-
mode data links and as a peer station in balanced connectionless-mode data links and is
capable of transmitting and receiving both command and response frames.
For the transfer of data between combined/peer stations, the data link control functions
illustrated in figure C are utilized. The data source in each combined/peer station
controls the data sink in the other combined/peer station by the use of select-type
commands. The information flows from the data source to the data sink, and the
acknowledgements are always transmitted in the opposite direction. The poll-type
commands may be used by each combined/peer station to solicit acknowledgements and
status responses from the other combined/peer station.
Select/information
Primary/ b Secondary/
Control Tributary
station
1 station
Acknowledgement
. /
Data source Data sink
Figure A -Unbalanced data link functions (case 1)
Poll/acknowledgement
Primary/
b Secondary/
Control
Tributary
station 4
’ station
Information
Data sink Data source
Figure B -Unbalanced data link functions (case 2)
I Select/information/acknowledgement/poll .
Combined/ b Combined./
Peer Peer
station station
- Select/information/acknowledgementipoll -
_ _ ._ _ _ ._
Data sink/data source - Data sink/data source
Figure C - Balanced data link functions
HDLC classes of procedures describe methods of data link operation which permit
synchronous or start/stop, code-transparent data transmission between data stations in a
variety of logical and physical configurations.
The classes are defined in a consistent
manner within the framework of an overall HDLC architecture. One of the purposes of
this International Standard is to maintain maximum compatibility between the basic types
of procedures, unbalanced, balanced and connectionless, as this is particularly desirable
for data stations with configurable capability, which may have the characteristics of a
primary, secondary, combined, control, tributary, or peer station, as required for a
specific instance of communication.
. . .
Vlll
ISO/IEC 13239: 1997(E)
OISOIIEC
Five fundamental classes of procedures (two unbalanced, one balanced, and two
connectionless) are defined herein. The unbalanced classes apply to both point-to-point
and multipoint configurations (as illustrated in figure D using the primary/secondary
nomenclature) over either dedicated or switched data transmission facilities. A
characteristic of the unbalanced classes is the existence of a single primary station at one
end of the data link plus one or more secondary stations at the other end(s) of the data
link. The primary station alone is responsible for data link management, hence the
designation “unbalanced” classes of procedures.
Primary/
I I4 b
Figure D -Unbalanced data link configuration
The unbalanced connectionless class applies to point-to-point configurations over either
dedicated or switched data transmission facilities, or to multipoint configurations over
dedicated data transmission facilities (as illustrated in figure D using the control/tributary
nomenclature). A characteristic of the unbalanced connectionless class is the existence of
a single control station at one end of the data link plus one or more tributary stations at
the other end(s) of the data link. The control station is responsible for determining when
a tributary station is permitted to send. Neither the control station nor the tributary
station(s) support any form of connection establishment/termination procedures, flow
control procedures, data transfer acknowledgement procedures, or
error recorvery
procedures, hence the designation ((connectionless)) class of procedures.
Combined/ Combined/
Peer Peer
I
station station
A B
Figure E - Balanced data link configuration
The balanced class applies to point-to-point configurations (as illustrated
in figure E
using the combined nomenclature) over either dedicated or switched data transmission
facilities. A characteristic of the balanced class is the existence of two data stations,
called combined stations, on a logical data link, that may share equally in the
responsibility for data link management, hence the designation “balanced” class of
procedures.
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ISO/IEC 13239: 1997(E)
0 ISO/IEC
The balanced connectionless class applies to point-to-point configurations over either
dedicated or switched data transmission facilities (as illustrated in figure E using the peer
nomenclature). A characteristic of the balanced connectionless class is the existence of
two data stations, called peer stations, on a data link, that are each independently in
control of when they can send. Neither peer station supports any form of connection
establishment/termination procedures, flow control procedures, data transfer
or error recovery procedures, hence the designation
acknowledgement procedures,
“connectionless” class of procedures.
For each class of procedures, a method of operation is specified in terms of the
capabilities of the basic repertoire of commands and responses that are found in that
class.
A variety of optional functions are also listed. Procedural descriptions for the use of the
optional functions are defined.
It is recognized that it is possible to construct symmetrical configurations for operation
on a single data circuit from the unbalanced classes of procedures which are defined in
this International Standard. For example, the combination of two unbalanced procedures
(with I frame flow as commands only) in opposite directions would create a symmetrical
point-to-point configuration (as illustrated in figure F).
Primary Secondary
Figure F - Symmetrical data link configuration
These HDLC procedures define the exchange identification (XID) command/response
frame as an optional function for exchange of data link information (identification,
parameters, functional capability, etc.). The content and format for a general purpose
XID frame information field is defined.
These HDLC procedures also specify the parameters and procedures which may be
employed by two data stations to mutually determine the data link layer addresses to be
used prior to logical data link establishment.

ISO/IEC 13239: 1997(E)
INTERNATIONAL STANDARD OISO/IEC
Information technology - Telecommunications and
information exchange between systems - High-level data
link control (HDLC) procedures
1 Scope
This International Standard specifies the frame structure, the elements of procedures, the classes of procedures, the content and
format of the general purpose Exchange Identification (XID) frame, and a means for resolution/negotiation of a data link layer
address in switched environments for data communication systems using bit-oriented high-level data link control (HDLC)
procedures.
NOTE - The use of the phrase ((bit-oriented)), referring to the HDLC control procedures, pertains to the allocation of a non-integral number of
bits to various subfields used for HDLC control purposes. However, the frame as an entirety may be constructed from octet-oriented units (e.g.,
start-stop mode) for transmission purposes.
The frame structure portion defines the relative positions of the various components of the basic frame and the bit combination
for the frame delimiting sequence (flag). The mechanisms used to achieve bit pattern independence (transparency) within the
frame are also defined. In addition, two frame checking sequences (FCS) are specified; the rules for address field extension are
defined; and the addressing conventions available are described.
The elements of procedures portion specifies elements of data link control procedures for synchronous or start/stop, code-
transparent data transmission using independent frame numbering in both directions.
terms of action commands at a
These HDLC elements of procedures are defined specifically in the s that occur on receipt of
secondary station, a tributary station, a peer station, or a combined station.
This International Standard is intended to cover a wide range of applications; for example one-way, two-way alternate or two-
way simultaneous data communication between data stations which are usually buffered, including operations on different types
of data circuits; for example multipoint/point-to-point, duplex/half-duplex, switched/non-switched, synchronous/start-stop, etc.
The defined elements of procedures are to be considered as a common basis for establishing different types of data link control
procedures. This International Standard does not define any single system and should not be regarded as a specification for a
data communication system. Not all of the commands or responses are required for any particular system implementation.
The classes of procedures portion describes the HDLC unbalanced classes of procedures, the HDLC balanced class of
procedures, and the HDLC connectionless classes of procedures for synchronous or start/stop data transmission.
For the unbalanced classes, the data link consists of a primary station plus one or more secondary stations and operates in either
the normal response mode or the asynchronous response mode in a point-to-point or multipoint configuration. For the balanced
class, the data link consists of two combined stations and operates in the asynchronous balanced mode in a point-to-point
configuration. For the unbalanced connectionless class, the data link consists of a control station plus one or more tributary
stations and operates in the unbalanced connectionless-mode in a point-to-point or multipoint configuration. For the balanced
connectionless class, the data link consists of two peer stations and operates in the balanced connectionless-mode in a point-to-
point configuration. In each class, a basic repertoire of commands and responses is defined, but the capability of the data link
may be modified by the use of optional functions.
in circumstances which require equ .a1 control at either end of the data link. Operational
Balanced operation is intended for use
requirements are covered in accordance with the overall HDLC architecture.
The content and format of the Exchange Identification (MD) frame portion builds on the fact that the principal use of the XID
frame is to exchange data link information between two or more HDLC stations. For the purpose of this International Standard,
data link information shall include any and all essential operational characteristics such as identification, authentication and/or
This International Standard defines a single-exchange
selection of optional functions and facilities concerning each station.
negotiation procedure for establishing operational characteristics when either one or more stations are capable of providing
multiple selections.
This International Standard provides a means for exchanging the necessary information to establish, at a minimum, a data link
connection between two correspondents wishing to communicate. It describes a general purpose XID frame information field
content and format for that purpose.

ISO/IEC 13239: 1997(E)
0 ISO/IEC
Mechanisms are provided to permit the general
It defines encoding for information related to the basic HDLC standards only.
purpose XID frame information field to be used to negotiate private parameters in a single XID exchange simultaneously with
negotiation of the defined basic parameters.
This International Standard does not limit or restrict the use of the XID frame information field from defining other standard
formats for use in specific applications.
The following are examples of potential uses of the XID command/response frame interchange:
Identification of the calling and called stations when using circuit switched networks (including switched network backup
a)
applications).
Identification of stations operating on non-switched networks requiring identification at start-up.
b)
The XID command frame with an individual, group or all-station address may be used to solicit XID response frame(s)
C)
from other station(s) on the data link, prior to or following data link establishment.
Negotiation of the Frame Check Sequence (FCS) to be used for subsequent information interchange, by stations that
support both 16-bit FCS and 32-bit FCS capabilities.
Convey higher layer information that may be required prior to data link establishment.
e)
Transmission of an XID response frame at any respond opportunity to request an XID exchange to modify some of the
f)
operational parameters (for example, window size) following data link establishment.
Negotiation of the number of protected bits in the frame when an Unnumbered Information with Header check (UIH)
g)
frame is used.
The means for resolution/negotiation of a data link layer address in switched environments portion is applicable to data stations
employing HDLC balanced classes of procedures which provide the XID command/response capability with the two specific
parameter fields, identified below. It is used to select a pair of operational link addresses when preassigned, system designated
Additional XID frame functions (including the
addresses are not known on an a priori basis; e.g., switched circuited data links.
exchange of operational parameters, command/response support, higher layer information, etc.) may be accomplished in
conjunction with data link layer address determination or following address determination, with additional XID frame exchanges.
NOTE - Address resolution procedures for situations where the remote DTE does not support XID frames, the “all-station” address, or complete
address support capabilities as defined in clause 8 below are not within the scope of this International Standard.
2 Normative references
The following standards contains provisions which, through reference in this text, constitute provisions of this International
All standards are subject to revision, and parties to
Standard. At the time of publication, the editions indicated were valid.
agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions
of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards.
ISO/IEC 646: 199 1, Information technology - IS0 7-bit coded character set for information interchange.
-Part 9: Data communication.
ISO/IEC 2382-9: 1995, Information technology - Vocabulary
IS0 7478: 1987, Information processing systems - Data communication - Multilink procedures.
ISO/IEC 7498-l : 1994, Information technology - Open Systems Interconnection -Basic Reference A4odel: The Basic Model.
ISO/IEC 7776: 1995, Information technology - Telecommunications and information exchange between systems - High-level
- Description of the X.25 LAPB-compatible DTE data link procedures.
data link control procedures
3 Definitions, acronyms and abbreviations
3.1 Definitions
The following definitions are to be used throughout this International Standard.
3.1.1 abort:
A function invoked by a sending primary, secondary, combined, control, tributary or peer station causing the recipient to discard
(and ignore) all bit sequences transmitted by the sender since the preceding flag sequence.
ISO/IEC 13239: 1997(E)
OISO/IEC
3.1.2 accept:
The condition assumed by a data station (primary, secondary, combined, control, tributary or peer station) upon accepting a
correctly received frame for processing.
3.1.3 address field (A):
The sequence of eight (or any multiple of eight, if extended) bits immediately following the opening flag sequence of a frame
identifying the secondary/combined or tributary/peer station sending (or designated to receive) the frame.
3.1.4 address field extension:
Enlarging the address field to include more addressing in formation.
3.1.5 address resolution/negotiation:
layer entity.
Procedure for exchanging/determining the data link layer identity of each data link
3.1.6 basic status:
A secondary/combined or tributary/peer station’s capability to send or receive a frame containing an information field.
3.1.7 centralized control:
station functions of the data link are centralized in one data station.
A control in which all the primary or control
3.1.8 combined station:
That part of a data station that supports the combined station control finctions of the data link.
NOTE - The combined station generates commands and responses for transmission and interprets received commands and responses. Specific
responsibilities assigned to a combined station include:
initialization of control signal interchange;
a>
b) organization of data flow;
interpretation of received commands and generation of appropriate responses; and
C)
d) actions regarding error control and error recovery functions at the data link layer.
3.1.9 command:
In data communication, an instruction represented in the control field of a frame and transmitted by the
primary/combined/control/peer station. It causes the addressed secondary/combined/tributary/peer station to execute a specific
data link control function.
3.1.10 command frame:
a) All frames transmitted by a primary/control station.
b) Those frames transmitted by a combined/peer station that contain the address of the other combined/peer station.
3.1.11 contention mode:
A mode of transmission which a transmitter can send on its own initiative.
3.1.12 control escape (CE):
The unique sequence of eight bits (10111110) employed to indicate the following octet has been modified according to the
transparency algorithm for start/stop transmission environments.
3.1.13 control field (C):
The sequence of eight (or 16/32/64, if extended) bits immediately following the address field of a frame.
NOTE - The content of the control field is interpreted by:
the receiving secondary/combined/tributary/peer station, designated by the address field, as a command instructing the performance of
a)
some specific function; and
b) the receiving primary/combined/control/peer station as a response from the secondary/combined/tributary/peer station, designated by the
address field, to one or more commands.
3.1.14 control field extension:
Enlarging the control field to include additional control information.

ISO/IEC 13239: 1997(E) 0 ISO/IEC
3.1.15 control station:
The data station that supports the control station control functions of the data link.
transmission interprets received responses. Specific responsibilities assigned to the
NOTE - The control station generates command for
control station include:
initialization of control signal interchange, and
b) organization of data flow.
3.1.16 data communication:
See ISO/IEC 2382-9, term 09.01.03.
3.1.17 data link:
See ISO/IEC 2382-9, term 09.04.08.
3.1.18 data link connection:
See ISO/IEC 7498-l : 1994.
3.1.19 data link layer:
The conceptual layer of control or processing logic existing in the hierarchical structure of a data station (primary, secondary,
combined, control, tributary or peer station) that is responsible for maintaining control of the data link.
These functions
NOTE - The data link layer functions provide an interface between the data station higher layer logic and the data link.
include:
transparency;
a)
b) address/control field interpretation;
command/response generation, transmission and interpretation; and
C>
frame check sequence computation and interpretation.
d)
3.1.20 data transmission:
See ISO/IEC 2382-9, term 09.01.02.
3.1.21 duplex transmission:
See ISO/IEC 2382-9, term 09.03.01.
3.1.22 exception condition:
The condition assumed by a secondary/combined station upon receipt of a frame which it cannot execute due either to a
transmission error or to an internal processing malfunction.
3.1.23 flag sequence (F):
The unique sequence of eight bits (01111110) employed to delimit the opening and closing of a frame.
3.1.24 format identifier:
Designator of one of 128 different standardized formats or one of 128 user-defined formats of the Exchange Identification (XID)
frame information field.
3.1.25 frame:
The sequence of address, control, information, and FCS fields, bracketed by opening and closing flag sequences.
and contains an address field, a control field and a frame check sequence. A frame may or
NOTE - A valid frame is at least 32 bits in length
may not include an information field.
3.1.26 frame check sequence (FCS):
The field immediately preceding the closing flag sequence of a frame, containing the bit sequence that provides for the detection
of transmission errors by the receiver.
3.1.27 group identifier:
Classifier of data link layer characteristics or parameters by function (for example, address resolution, parameter negotiation, user
data).
ISO/IEC 13239: 1997(E)
OISO/IEC
3.1.28 half-duplex transmission:
See ISO/IEC 2382-9, term 09.03.02.
3.1.29 HDLC-based protocol:
A protocol which is a subset of the elements and classes of procedure and optional functions defined in the HDLC standard, and
adopted as a standard by IS0 or a recognized international standards body (e.g., ITU-T).
3.1.30 higher layer:
The conceptual layer of control or processing logic existing in the hierarchical structure of a data station (primary, secondary,
combined, control, tributary or peer station) that is above the data link layer and upon which the performance of data link layer
functions are dependent; for example device control, buffer allocation, station management, etc.
3.1.31 information field (INFO):
The sequence of bits, occurring between the last bit of the control field and the first bit of the frame check sequence.
NOTE - The information field contents of I, UI, and UIH frames are not interpreted at the data link layer.
3.1.32 initiating combined station:
A station that sends the initial XID command frame as part of the address resolution process.
3.1.33 interframe time fill:
The sequence or condition transmitted between frames.
3.1.34 intraframe time fill:
In start/stop transmission, the sequence or condition transmitted within a frame when the next octet is not available for
contiguous transmission immediately following the preceding octet. For synchronous transmission, there is IM protim fw
intraframe time fill.
3.1.35 invalid frame:
opening sequence, that either
A sequence of bits, following the receipt of an
flag
is terminated by an abort sequence; or
a)
contains less than 32 bits before an apparent closing flag sequence is detected.
b)
3.1.36 layer parameter:
parameters, and their values, available or chosen.
The specification of data link layer characteristics and
3.1.37 non-initiating combined station:
A station that waits for the other combined station to send the initial XID command frame as part of the address resoiution
process.
3.1.38 peer station:
The data station that supports the peer station control functions of the data link.
NOTE - The peer station generates commands for transmission and interprets received commands and responses.
3.1.39 primary station:
The data station that supports the primary station control functions of the data link.
responses. Specific responsibilities assigned to the
NOTE - The primary station generates commands for transmission and interprets received
primary station include:
initialization of control signal interchange;
organization of data flow; and
actions regarding error control and error recovery functions at the data link layer.
C)
3.1.40 primary/secondary station:
The general case where the station may be either a primary station or a secondary station.

ISO/IEC 13239: 1997(E)
0 ISO/IEC
3.1 .41 private parameter:
not defined in the basic HDLC standards.
An implementation-specific data link layer parameter
3.1.42 response:
frame that advises the
In data communication, a reply represented in the control field of a response
primary/combined/control/peer station with respect to the action taken by the secondary/combined/tributary/peer station to one or
more commands.
3.1.43 response frame:
station.
All frames transmitted by a secondary/tributary
a)
Those frames transmitted by a combined/peer station that contain the address of the transmitting combined/peer station.
b)
3.1.44 secondary station:
The data station that executes data link control functions as instructed by the primary station.
NOTE - A secondary station inteq.xets received commands and generates responses for transmission.
3.1.45 secondary station status:
respect to processing the series of commands received from the primary station.
The current condition of a secondary station with
3.1.46 single-exchange negotiation procedure:
The initiating station indicates its “menu” of capabilities in its command frame, and the responding station indicates its choices
from the menu in its response frame.
3.1.47 tributary station:
The data station that executes data link control functions as instructed by the control station.
NOTE
- The tributary station interprets received commands and generates responses for transmission.
3.1.48 two-way alternate data communication:
See ISO/IEC 2382-9, term 09.0503.
3.1.49 two-way simultaneous data communication:
See ISO/IEC 2382-9, term 09.0502.
3.1.50 unique identifier:
A unique bit/character sequence (for example, global telephone number, station identification, or equivalent) associated with
each station.
3.1.51 unnumbered commands:
control field.
The commands that do not contain sequence numbers in the
3.1.52 unnumbered responses:
The responses that do not contain sequence numbers in the control field.
3.1.53 user data:
layer.
The information obtained from or delivered to the user of the data link
3.2 Acronyms and abbreviations
The following acronyms and abbreviations are used commonly throughout this International Standard.
A Address field
ABM Asynchronous Balanced Mode
ADM Asynchronous Disconnected Mode
Asynchronous Response Mode
B Binary encoded
BAC Balanced operation Asynchronous balanced mode Class
BCC Balanced operation Connectionless-mode Class

ISO/IEC 13239: 1997(E)
OISOIIEC
BCM Balanced Connectionless Mode
C Control field
CE
Control Escape
C/R Command/Response
F Flag sequence
F Final bit
FI
Format Identifier
DC1 Device Control One
DC3 Device Control Three
DCE Data Circuit-terminating Equipment
DISC Disconnect
DM Disconnected Mode
DTE Data Terminal Equipment
E
bit Encoded
FCS Frame Check Sequence
FRMR FRaMe Reject
GI Group Identifier
GL Group Length
HDLC High-level Data Link Control
Information frame
IEC International Electrotechnical Commission
IM Initialization Mode
INFO INFOrmation field
IS0 International Organization for Standardization
ITU-T
International Telecommunications Union - Telecommunication Standardization Sector
LAPB
Link Access Procedure Balanced
LSB Least Significant Bit
M Modifier function bit
MSB Most Significant Bit
MT1
Multilink lost frame Timer 1
MT2 Multilink group busy Timer 2
MT3 Multilink reset confirmation Timer 3
MW Multilink Window size
MX Multilink guard region window size
N Number of octets
Send sequence Number
N(S)
Receive sequence Number
N(R)
NA Not Applicable
NDM Normal Disconnected Mode
NRM Normal Response Mode
P Poll bit
P/F Poll/Final bit
PI Parameter Identifier
PL Parameter Length
Pri Primary
PV
Parameter Value
RD Request Disconnect
REJ REJect
RIM Request Initialization Mode
RNR Receive Not Ready
RR Receive Ready
RSET ReSET
S Supervisory frame
S Supervisory function bit
SABM Set Asynchronous Balanced Mode
SABME Set Asynchronous Balanced Mode Extended
SARM Set Asynchronous Response Mode
SARME Set Asynchronous Response Mode Extended
SBDPT Seven-Bit Data Path Transparency
SD System Defined
Set
Secondary
SIM
Set Initialization Mode
SM Set Mode
SNRM Set Normal Response Mode
SNRME Set Normal Response Mode Extended

ISO/IEC 13239: 1997(E) 0 ISO/IEC
SREJ Selective REJect
TBD To Be Determined
TEST TEST
TR Technical Report
TWA Two-Way Alternate
TWS Two-Way Simultaneous
U Unnumbered frame
...