Information technology — Data communications — X.25 Packet Layer Protocol for Data Terminal Equipment

This International Standard specifies the procedures, formats and facilities at the Packet Layer for Data Terminal Equipment (DTE) operating in conformance with ITU-T Recommendation X.25. Both Virtual Call and Permanent Virtual Circuit modes of operation are covered. The Packet Layer protocol specified herein can be used in both Open Systems Interconnection (OSI) and non-OSI environments. When used within the context of OSI, the Packet Layer protocol is encompassed in the Network Layer of the OSI Reference Model, ITU-T Rec. X.200 | ISO/IEC 7498-1. This International Standard covers DTE operation at the Packet Layer when accessing a public or private packet-switched network conforming to ITU-T Recommendation X.25 by means of a dedicated path or a circuit-switched connection. It also covers the additional Packet Layer procedures necessary for two DTEs conforming to this International Standard to communicate directly (i.e., without an intervening packet-switched network) over a dedicated path, a circuit-switched connection, or a local area network (LAN). This International Standard also covers private networks that use ITU-T Recommendation X.25 to connect to packet-switched public data networks and that may also offer an X.25 interface to a DTE (see annex A). To evaluate conformance of a particular implementation, it is necessary to have a statement of which capabilities and options have been implemented. Such a statement is called a Protocol Implementation Conformance Statement (PICS), as defined in ITU-T Rec. X.290 | ISO/IEC 9646-1. Annex B provides the PICS proforma in accordance with the relevant guidance given in ITUT Rec. X.296 | ISO/IEC 9646-7. The first edition of this International Standard was based on the 1984 CCITT Red Book text of Recommendation X.25. It also contained the necessary provisions for compatibility with the earlier 1980 CCITT Yellow Book text of Recommendation X.25. The second edition was based on the 1988 CCITT Blue Book text of Recommendation X.25. The third edition is based upon the 1993 version of X.25. This fourth edition is based on the 1996 version of X.25. Retained within this fourth edition are the necessary provisions for compatibility with the 1993, 1988, 1984 and 1980 versions of X.25. The differences between various editions of this International Standard are summarized in annex C. CCITT Recommendation X.613 (1992) | ISO/IEC 10588 : 1993, Information technology Use of X.25 Packet Layer Protocol in conjunction with X.21/X.21bis to provide the OSI connectionmode Network Service CCITT Recommendation X.614 (1992) | ISO/IEC 10732 : 1993, Information technology Use of X.25 Packet Layer Protocol to provide the OSI connection-mode Network Service over the telephone network

Technologies de l'information — Communication de données — Protocole X.25 de couche paquet pour terminal de données

General Information

Status
Published
Publication Date
15-Nov-2000
Current Stage
9093 - International Standard confirmed
Start Date
15-Sep-2005
Completion Date
15-Sep-2005
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ISO/IEC 8208:2000 - Information technology -- Data communications -- X.25 Packet Layer Protocol for Data Terminal Equipment
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INTERNATIONAL ISO/IEC
STANDARD 8208
Fourth edition
2000-11-01
Information technology — Data
communications — X.25 Packet Layer
Protocol for Data Terminal Equipment
Technologies de l'information — Communication de données —
Protocole X.25 de couche paquet pour terminal de données
Reference number
ISO/IEC 8208:2000(E)
ISO/IEC 2000
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ISO/IEC 8208:2000(E)
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ii © ISO/IEC 2000 – All rights reserved
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ISO/IEC 8208 : 2000(E)
CONTENTS
Page

Foreword ................................................................................................................................ vi

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

2 Normative references ............................................................................................................1

2.1 Identical Recommendations | International Standards .....................................................1

2.2 Paired Recommendations | International Standards equivalent in technical content........2

2.3 Additional references .......................................................................................................2

3 General considerations .........................................................................................................2

3.1 Compatibility with versions of Recommendation X.25 ...................................................3

3.2 Environments...................................................................................................................5

3.3 Differences in DTE/DTE and DTE/DCE operation .........................................................5

3.4 Operation over circuit-switched connections...................................................................6

3.5 Provision of the OSI Network Service.............................................................................7

3.6 External Packet Layer interactions...................................................................................7

3.7 Logical channels ..............................................................................................................7

3.8 Packet Layer entity...........................................................................................................8

3.9 Packet types .....................................................................................................................9

3.10 Procedures for initialization...........................................................................................9

4 Procedures for restart...........................................................................................................9

4.1 Originating a restart request...........................................................................................10

4.2 Receiving a restart indication.........................................................................................12

4.3 Restart collision .............................................................................................................12

4.4 Restart confirmation....................................................................................................... 12

4.5 Determining “DTE” or “DCE” characteristics...............................................................12

5 Procedures for Virtual Call setup and clearing ................................................................13

5.1 Ready state.....................................................................................................................13

5.2 Procedures for Virtual Call setup...................................................................................13

5.3 Rejecting a call...............................................................................................................15

5.4 Aborting a call request...................................................................................................15

5.5 Procedures for Virtual Call clearing ..............................................................................15

6 Procedures for data and interrupt transfer.......................................................................16

6.1 States for data and interrupt transfer ..............................................................................17

6.2 Maximum User Data Field length of DATA packets .....................................................17

6.3 Delivery Confirmation bit..............................................................................................17

6.4 More Data mark ............................................................................................................. 18

6.5 Complete packet sequence .............................................................................................18

6.6 Qualifier bit....................................................................................................................18

6.7 Fragmentation and reassembly of messages...................................................................19

6.8 Procedures for interrupt .................................................................................................20

6.9 Transit delay of DATA packets......................................................................................21

7 Procedures for flow control................................................................................................21

7.1 Flow control...................................................................................................................22

7.2 Throughput characteristics and throughput classes........................................................25

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ISO/IEC 8208 : 2000(E)

8 Procedures for reset ......................................................................................................... ... 25

8.1 Originating a reset request .................................................................................................27

8.2 Receiving a reset indication ............................................................................................... 27

8.3 Reset collision.................................................................................................................... 27

8.4 Reset confirmation............................................................................................................. 27

9 Effects of clear, reset, and restart procedures on the transfer of packets ....................... 27

10 Effects of Layers 1 and 2 on the Packet Layer................................................................ 28

11 Error handling .............................................................................................................. .... 28

11.1 The DIAGNOSTIC packet............................................................................................... 29

11.2 Nonreceipt of window-rotation information .................................................................... 29

11.3 Receipt of erroneous DATA packets ............................................................................... 30

12 Packet formats................................................................................................................... 31

12.1 General............................................................................................................................. 31

12.2 Call setup and call clearing packets ................................................................................. 33

12.3 DATA and interrupt packets............................................................................................ 42

12.4 Flow control packets........................................................................................................ 44

12.5 Reset packets ................................................................................................................... 45

12.6 Restart packets ................................................................................................................. 47

12.7 DIAGNOSTIC packet...................................................................................................... 48

12.8 REJECT packet................................................................................................................ 49

12.9 Registration packets......................................................................................................... 50

13 Procedures for optional user facilities ............................................................................. 52

13.1 On-line Facility Registration............................................................................................ 52

13.2 Extended and Super Extended Packet Sequence Numbering .......................................... 59

13.3 D-bit Modification........................................................................................................... 60

13.4 Packet Retransmission ..................................................................................................... 60

13.5 Incoming Calls Barred ..................................................................................................... 61

13.6 Outgoing Calls Barred ..................................................................................................... 61

13.7 One-way Logical Channel Outgoing................................................................................ 61

13.8 One-way Logical Channel Incoming ............................................................................... 61

13.9 Nonstandard Default Packet Sizes ................................................................................... 61

13.10 Nonstandard Default Window Sizes .............................................................................. 61

13.11 Default Throughput Classes Assignment....................................................................... 62

13.12 Flow Control Parameter Negotiation ............................................................................. 62

13.13 Throughput Class Negotiation Facilities........................................................................ 63

13.14 Closed User Group related facilities .............................................................................. 64

13.15 Bilateral Closed User Group related facilities................................................................ 68

13.16 Fast Select...................................................................................................................... 69

13.17 Fast Select Acceptance .................................................................................................. 70

13.18 Reverse Charging........................................................................................................... 70

13.19 Reverse Charging Acceptance ....................................................................................... 70

13.20 Local Charging Prevention ............................................................................................ 70

13.21 Network User Identification (NUI) related facilities...................................................... 71

13.22 Charging Information..................................................................................................... 71

13.23 ROA related facilities ....................................................................................................73

13.24 Hunt Group.................................................................................................................... 73

13.25 Call Redirection and Call Deflection related facilities................................................... 73

13.26 Called Line Address Modified Notification................................................................... 76

13.27 Transit Delay Selection and Indication.......................................................................... 76

13.28 Alternative Addressing Related Facilities...................................................................... 76

13.29 TOA/NPI address subscription ...................................................................................... 78

13.30 Reference Number ......................................................................................................... 78

14 Procedures for optional ITU-T specified DTE facilities................................................. 80

14.1 Calling Address Extension............................................................................................... 80

14.2 Called Address Extension................................................................................................ 80

14.3 Minimum Throughput Class Negotiation ........................................................................ 80

14.4 End-to-End Transit Delay Negotiation ............................................................................ 81

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ISO/IEC 8208 : 2000(E)

14.5 Priority.............................................................................................................................81

14.6 Protection.........................................................................................................................81

14.7 Expedited Data Negotiation.............................................................................................81

15 Format for Facility Field in call setup/clearing packets .................................................82

15.1 General.........................................................................................................................82

15.2 Coding of the Facility Field for optional user facilities ...............................................83

15.3 Coding of the Facility Field for ITU-T specified DTE facilities..................................89

16 Format for Registration Field in registration packets....................................................92

16.1 General.........................................................................................................................92

16.2 Coding of the Registration Field for registration-facilities ..........................................93

17 Diagnostic codes ................................................................................................................95

18 Timers and retransmission counts .................................................................................101

19 State diagrams.................................................................................................................105

20 State tables.......................................................................................................................111

21 Conformance ...................................................................................................................120

21.1 Static conformance.....................................................................................................120

21.2 Protocol Implementation Conformance Statement ....................................................120

21.3 Dynamic conformance ...............................................................................................120

Annexes

A Private networks.............................................................................................................123

B PICS Proforma ...............................................................................................................131

C Differences between various editions of ISO/IEC 8208...............................................159

D Abbreviations..................................................................................................................169

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ISO/IEC 8208 : 2000(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.

International Standards are drafted in accordance with the rules given in the ISO/IEC

Directives, Part 3.

In the field of information technology, ISO 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.

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.
International Standard ISO/IEC 8208 was prepared by Joint Technical Committee
ISO/IEC JTC 1, Information technology, Subcommittee SC 6, Telecommunications and
information exchange between systems.

This fourth edition cancels and replaces the third edition (ISO/IEC 8208:1995), which

has been technically revised.

Annexes A and B form a normative part of this International Standard. Annexes C and D

are for information only.
 ISO/IEC 2000 – All rights reserved
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INTERNATIONAL STANDARD ISO/IEC 8208 : 2000(E)
Information technology  Data communications 
X.25 Packet Layer Protocol for Data Terminal Equipment
It should be noted that this International Standard and ITU-T
1 Scope
Recommendation X.25 as it applies to DTEs are different in
This International Standard specifies the procedures, formats and
scope. This International Standard contains the specifications that
facilities at the Packet Layer for Data Terminal Equipment (DTE)
ITU-T Recommendation X.25 places on DTEs. In addition, this
operating in conformance with ITU-T Recommendation X.25.
International Standard contains added specifications to facilitate
Both Virtual Call and Permanent Virtual Circuit modes of
interworking between DTEs and to cover direct DTE-to-DTE
operation are covered.
operation. This broader scope has to be recognized in the
application of this International Standard.
The Packet Layer protocol specified herein can be used in both
Open Systems Interconnection (OSI) and non-OSI environments.

When used within the context of OSI, the Packet Layer protocol 2 Normative references

is encompassed in the Network Layer of the OSI Reference
The following normative documents contain provisions which,
Model, ITU-T Rec. X.200 | ISO/IEC 7498-1.
through reference in this text, constitute provisions of this
International Standard. For dated references, subsequent
This International Standard covers DTE operation at the Packet
amendments to, or revisions of, any of these publications do not
Layer when accessing a public or private packet-switched
apply. However, parties to agreements based on this International
network conforming to ITU-T Recommendation X.25 by means
Standard are encouraged to investigate the possibility of applying
of a dedicated path or a circuit-switched connection. It also
the most recent editions of the normative documents indicated
covers the additional Packet Layer procedures necessary for two
below. For undated references, the latest edition of the normative
DTEs conforming to this International Standard to communicate
document referred to applies. Members of ISO and IEC maintain
directly (i.e., without an intervening packet-switched network)
registers of currently valid International Standards. The
over a dedicated path, a circuit-switched connection, or a local
Telecommunication Standardization Bureau of the ITU maintains
area network (LAN).
a register of currently valid ITU-T Recommendations.
This International Standard also covers private networks that use
2.1 Identical Recommendations | International
ITU-T Recommendation X.25 to connect to packet-switched
Standards
public data networks and that may also offer an X.25 interface to
a DTE (see annex A).
ITU-T Recommendation X.200 (1994) | ISO/IEC 7498-1 : 1994,
Information technology  Open Systems Interconnection 
To evaluate conformance of a particular implementation, it is
Basic Reference Model: The Basic Model
necessary to have a statement of which capabilities and options
have been implemented. Such a statement is called a Protocol
ITU-T Recommendation X.212 (1995) | ISO/IEC 8886 : 1996,
Implementation Conformance Statement (PICS), as defined in
Information technology  Open Systems Interconnection 
ITU-T Rec. X.290 | ISO/IEC 9646-1. Annex B provides the PICS
Data link service definition
proforma in accordance with the relevant guidance given in ITU-
ITU-T Recommendation X.213 (1995) | ISO/IEC 8348 : 1996,
T Rec. X.296 | ISO/IEC 9646-7.
Information technology  Open Systems Interconnection 
The first edition of this International Standard was based on the
Network service definition
1984 CCITT Red Book text of Recommendation X.25. It also
ITU-T Recommendation X.263 (1998) | ISO/IEC TR 9577:1999,
contained the necessary provisions for compatibility with the
earlier 1980 CCITT Yellow Book text of Recommendation X.25.
Information technology  Protocol identification in the network
The second edition was based on the 1988 CCITT Blue Book layer
text of Recommendation X.25. The third edition is based upon
ITU-T Recommendation X.273 (1994) | ISO/IEC 11577 : 1995,
the 1993 version of X.25. This fourth edition is based on the
Information technology  Open Systems Interconnection 
1996 version of X.25. Retained within this fourth edition are the
Network layer security protocol
necessary provisions for compatibility with the 1993, 1988, 1984
and 1980 versions of X.25. The differences between various
CCITT Recommendation X.612 (1992) | ISO/IEC 9574 : 1992,
editions of this International Standard are summarized in annex
Information technology  Provision of the OSI connection-mode
network service by packet-mode terminal equipment connected to
an integrated services digital network (ISDN)
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ISO/IEC 8208 : 2000(E)

CCITT Recommendation X.613 (1992) | ISO/IEC 10588 : 1993, ITU-T Recommendation X.32 (1996), Interface between data

terminal equipment (DTE) and data circuit-terminating
Information technology  Use of X.25 Packet Layer Protocol in

conjunction with X.21/X.21bis to provide the OSI connection- equipment (DCE) for terminals operating in the packet mode and

accessing a packet switched public data network through a
mode Network Service
public switched telephone network or an integrated services
CCITT Recommendation X.614 (1992) | ISO/IEC 10732 : 1993,
digital network or a circuit switched public data network
Information technology  Use of X.25 Packet Layer Protocol to
ITU-T Recommendation X.75 (1996), Packet-switched
provide the OSI connection-mode Network Service over the
signalling system between public networks providing data
telephone network
transmission services
2.2 Paired Recommendations | International
ITU-T Recommendation X.96 (1993), Call progress signals in
Standards equivalent in technical content
public data networks
− CCITT Recommendation T.50 (1992), International
ITU-T Recommendation X.121 (1996), International numbering
Reference Alphabet (IRA)
plan for public data networks
ISO/IEC 646 : 1991, Information technology  ISO 7-bit
ITU-T Recommendation X.301 (1996), Description of the
coded character set for information interchange
general arrangements for call control within a subnetwork and
− ITU-T Recommendation X.223 (1993), Use of X.25 to
between subnetworks for the provision of data transmission
provide the OSI connection-mode network service for ITU-T
services
applications
CCITT Recommendation X.610 (1992), Provision and support
ISO/IEC 8878 : 1992, Information technology 
of the OSI connection-mode network service
Telecommunications and information exchange between
ISO/IEC 7776 : 1995, Information technology 
systems  Use of X.25 to provide the OSI Connection-mode
Telecommunications and information exchange between systems
Network Service
 High-level data link control procedures — Description of the
− ITU-T Recommendation X.290 (1995), OSI conformance
X.25 LAPB-compatible DTE data link procedures
testing methodology and framework for protocol
ISO/IEC 8881 : 1989, Information processing systems  Data
Recommendations for ITU-T applications  General
communications  Use of the X.25 packet level protocol in local
concepts
area networks
ISO/IEC 9646-1 : 1994, Information technology  Open
ISO/IEC TR 10029 : 1989, Information technology 
Systems Interconnection  Conformance testing
Telecommunications and information exchange between systems
methodology and framework  Part 1: General concepts
 Operation of an X.25 interworking unit
− ITU-T Recommendation X.296 (1995), OSI conformance
ISO/IEC 10039 : 1991, Information technology  Open Systems
testing methodology and framework for protocol
Interconnection  Local area networks  Medium Access
Recommendations for ITU-T applications  Implementation
Control (MAC) service defintion
Conformance Statements
ISO/IEC TR 13532 : 1995, Information technology 
ISO/IEC 9646-7 : 1995, Information technology  Open
Telecommunications and information exchange between systems
Systems Interconnection — Conformance testing
 Protocol combinations to provide and support the OSI
methodology and framework  Part 7: Implementation
network service
Conformance Statements
RFC 1166, Internet numbers, July 1990.
2.3 Additional references
CCITT Recommendation D.12 (1988), Measurement unit for
3 General considerations
charging by volume in the international packet-switched data
This International Standard defines, from the viewpoint of a
communication service
DTE, the Packet Layer, which governs the transfer of packets at a
ITU-T Recommendation X.2 (1996), International data
DTE/DCE or DTE/DTE interface. On the transmitting side, the
transmission services and optional user facilities in public data
Packet Layer in a sending DTE performs the basic function of
networks and ISDNs
packetizing messages delivered by a higher layer entity in the
same DTE before giving the information to the Data Link Layer
ITU-T Recommendation X.25 (1996), Interface between data
for transmission to a DXE. On the receiving side, the Packet
terminal equipment (DTE) and data circuit-terminating
Layer in a DTE performs the basic functions of receiving packets
equipment (DCE) for terminals operating in the packet mode and
from the Data Link Layer, checking packets for correctness,
connected to public data networks by dedicated circuit
stripping off packet headers, and formulating messages from the
ITU-T Recommendation X.29 (1997), Procedures for the
exchange of control information and user data between a packet
assembly/disassembly (PAD) facility and a packet mode DTE or
The term “DXE” is used in those contexts where it would not matter
another PAD
whether a DTE or a DCE was being referred to. Therefore, this
International Standard can be viewed as defining the Packet Layer at the
ITU-T Recommendation X.31 (1995), Support of packet mode
DTE/DXE interface.
terminal equipment by an ISDN
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ISO/IEC 8208 : 2000(E)

packetized user data and passing them to a higher layer entity in c) a negligible packet-loss and duplication rate.

the DTE.
The Packet Layer provides the following functional capabilities
that facilitate reliable and efficient data communications:
This International Standard presents a description of the Packet
Layer for “Virtual Call” service and “Permanent Virtual Circuit”
a) multiplexing — the ability to support multiple
service.
communications;
The following information is pr
...

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