Information technology — Telecommunications and information exchange between systems — High-level data link control (HDLC) procedures

This International Standard specifies the frame structures, 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 format and the nonbasic frame format. The mechanisms used to achieve bit pattern independence (transparency), where and when required, within the frame are also defined. In addition, three 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, codetransparent data transmission using independent frame numbering in both directions. These HDLC elements of procedures are defined specifically in terms of the actions that occur on receipt of commands at a 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 twoway 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/startstop, 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-topoint 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. Balanced operation is intended for use in circumstances which require equal control at either end of the data link. Operational requirements are covered in accordance with the overall HDLC architecture. The content and format of the Exchange Identification (XID) 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, ISO/IEC 13239:2002(E)

Technologies de l'information — Télécommunications et échange d'information entre systèmes — Procédures de commande de liaison de données à haut niveau (HDLC)

General Information

Status
Published
Publication Date
21-Aug-2002
Current Stage
9093 - International Standard confirmed
Start Date
20-Dec-2007
Completion Date
20-Dec-2007
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INTERNATIONAL ISO/IEC
STANDARD 13239
Third edition
2002-07-15
Information technology —
Telecommunications and information
exchange between systems — High-level
data link control (HDLC) procedures
Technologies de l'information — Télécommunications et échange
d'information entre systèmes — Procédures de commande de liaison de
données à haut niveau (HDLC)
Reference number
ISO/IEC 13239:2002(E)
ISO/IEC 2002
---------------------- Page: 1 ----------------------
ISO/IEC 13239:2002(E)
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ii © ISO/IEC 2002 – All rights reserved
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ISO/IEC 13239:2002(E)
Contents Page

Foreword.......................................................................................................................................................................................v

Introduction .................................................................................................................................................................................vi

1 Scope................................................................................................................................................................................1

2 Normative references .....................................................................................................................................................2

3 Definitions, acronyms and abbreviations.....................................................................................................................3

3.1 Definitions.......................................................................................................................................................................3

3.2 Acronyms and abbreviations.........................................................................................................................................8

4 HDLC frame structure ................................................................................................................................................10

4.1 Frame formats ..............................................................................................................................................................11

4.2 Elements of the frame ..................................................................................................................................................12

4.3 Transparency................................................................................................................................................................15

4.4 Transmission considerations .......................................................................................................................................17

4.5 Inter-frame time fill .....................................................................................................................................................17

4.6 Invalid frame ................................................................................................................................................................17

4.7 Extensions .....................................................................................................................................................................18

4.8 Addressing conventions ...............................................................................................................................................18

4.9 Frame format field .......................................................................................................................................................19

5 HDLC elements of procedures ....................................................................................................................................21

5.1 Data link channel states ...............................................................................................................................................21

5.2 Modes ............................................................................................................................................................................22

5.3 Control field formats....................................................................................................................................................25

5.4 Control field parameters .............................................................................................................................................27

5.5 Commands and responses ...........................................................................................................................................31

5.6 Exception condition reporting and recovery .............................................................................................................53

6 HDLC classes of procedures........................................................................................................................................58

6.1 Types of data station ....................................................................................................................................................59

6.2 Configurations..............................................................................................................................................................60

6.3 Operational modes .......................................................................................................................................................60

6.4 Addressing scheme.......................................................................................................................................................60

6.5 Send and receive state variables .................................................................................................................................60

6.6 Fundamental classes of procedures ............................................................................................................................60

6.7 Optional functions........................................................................................................................................................62

6.8 Consistency of classes of procedures ..........................................................................................................................62

6.9 Conformance to the HDLC classes of procedures.....................................................................................................62

6.10 Method of indicating classes and optional functions.................................................................................................63

6.11 Unbalanced operation (point-to-point and multipoint) ............................................................................................66

6.12 Balanced operation (point-to-point) ...........................................................................................................................69

6.13 Unbalanced connectionless operation (point-to-point and multipoint) ...................................................................73

6.14 Balanced connectionless operation (point-to-point)..................................................................................................76

6.15 Uses of the optional functions......................................................................................................................................78

7 General purpose Exchange Identification (XID) frame............................................................................................85

7.1 General purpose XID frame information field structure .........................................................................................85

7.2 General purpose XID frame information field encoding..........................................................................................85

7.3 Single-frame exchange negotiation process................................................................................................................91

7.4 Frame check sequence negotiation rules ....................................................................................................................92

7.5 Rules for negotiation use of the frame format field in non-basic frame format mode...........................................93

8 Resolution/negotiation of data link layer address in switched environments .........................................................93

8.1 Operational requirements ...........................................................................................................................................93

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ISO/IEC 13239:2002(E)

8.2 Address resolution ....................................................................................................................................................... 94

Annex A (informative) Explanatory notes on the implementation of the frame checking sequence .................................. 95

Annex B (informative) Example of the use of commands and responses .............................................................................. 97

Annex C (informative) Time-out function considerations for NRM, ARM and ABM ...................................................... 118

Annex D (informative) Examples of typical HDLC procedural subsets.............................................................................. 120

Annex E (informative) Illustrative examples of 16/32-bit FCS negotiation ........................................................................ 123

Annex F (informative) Guidelines for communicating with LAPB X.25 DTEs.................................................................. 125

Annex G (informative) Examples of information field encoding in multi-selective reject frames .................................... 126

Annex H (normative) Frame format types............................................................................................................................. 127

iv © ISO/IEC 2002 – All rights reserved
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ISO/IEC 13239:2002(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the

specialized system for worldwide standardization. National bodies that are members of ISO or IEC participate in the

development of International Standards through technical committees established by the respective organization to deal with

particular fields of technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other

international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the work. In

the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.

The main task of the joint technical committee is to prepare International Standards. 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.

Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent

rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.

ISO/IEC 13239 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology, Subcommittee SC 6,

Telecommunications and information exchange between systems.

This third edition cancels and replaces the second edition (ISO/IEC 13239:2000), which has been technically revised. It also

cancels and replaces ISO/IEC 3309:1993, ISO/IEC 4335:1993, ISO/IEC 7809:1993 and ISO/IEC 8885:1993.

Annex H forms a normative part of this International Standard. Annexes A to G are for information only.

© ISO/IEC 2002 – All rights reserved v
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ISO/IEC 13239:2002(E)
Introduction

This third edition adds a new frame format type to Annex H – Frame format types. This frame format type is used in those

environments where additional error protection, identification of both the source and the destination(s), and/or longer frame

sizes are needed.

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.

The information flows from the data source to the data sink, and the acknowledgements are always transmitted in the opposite

direction.

These two cases of data link control may be combined so that the data link becomes capable of two-way alternate

communication, or two-way simultaneous communication.
vi © ISO/IEC 2002 – All rights reserved
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ISO/IEC 13239:2002(E)
Select/information
Primary/
Secondary/
Control
Tributary
station station
Acknowledgement
Data source Data sink
Figure A — Unbalanced data link functions (case 1)
Poll/acknowledgement
Primary/
Secondary/
Control
Tributary
station station
Information
Data sink Data source
Figure B — Unbalanced data link functions (case 2)
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/acknowledgement/poll
Combined/ Combined/
Peer Peer
station station
Select/information/acknowledgement/poll
Data sink/data source Data sink/data source
Figure C — Balanced data link functions
Data link configurations

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.

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.
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ISO/IEC 13239:2002(E)
Primary/
Control
station
Secondary/ Secondary/
Tributary Tributary
station station
A N
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.

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.
Combined/ Combined/
Peer Peer
station station
A B
Figure E — Balanced data link configuration

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 acknowledgement procedures, or error recovery procedures, hence the designation "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).
viii © ISO/IEC 2002 – All rights reserved
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ISO/IEC 13239:2002(E)
Primary Secondary
station station
1 1
Secondary Primary
station station
2 2
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 2002 – All rights reserved ix
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INTERNATIONAL STANDARD ISO/IEC 13239:2002(E)
Information technology — Telecommunications and information exchange
between systems — High-level data link control (HDLC) procedures
1 Scope

This International Standard specifies the frame structures, 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 format and the non-

basic frame format. The mechanisms used to achieve bit pattern independence (transparency), where and when required, within

the frame are also defined. In addition, three 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.

These HDLC elements of procedures are defined specifically in terms of the actions that occur on receipt of commands at a

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.

Balanced operation is intended for use in circumstances which require equal control at either end of the data link. Operational

requirements are covered in accordance with the overall HDLC architecture.

The content and format of the Exchange Identification (XID) 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,

© ISO/IEC 2002 – All rights reserved 1
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ISO/IEC 13239:2002(E)

data link information shall include any and all essential operational characteristics such as identification, authentication and/or

selection of optional functions and facilities concerning each station. This International Standard defines a single-exchange

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.

It defines encoding for information related to the basic HDLC standards only. Mechanisms are provided to permit the general

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:

a) Identification of the calling and called stations when using circuit switched networks (including switched network backup

applications).
b) Identification of stations operating on no
...

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