ISO/IEC 8208:1995
(Main)Information technology — Data communications — X.25 Packet Layer Protocol for Data Terminal Equipment
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
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Standards Content (Sample)
INTERNATIONAL . ISO/IEC
STANDARD 8208
Third edition
1995-08-01
Information technology - Data
- X.25 Packet Layer
communications
Protocol for Data Terminal Equipment
Technologies de I’in formation - Communication de don&es -
Protocole X.25 de couche paquet pour terminal de don&es
Reference number
lSO/IEC 8208:1995(E)
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ISO/IEC 8208: 1995(E)
CONTENTS
1
Scope . . . . . . . . . . . . .*.~.~.
1
1
...........................................................................................................
2 Normative references.
1
....................................................
2.1 Identical Recommendations 1 International Standards
..... 2
2.2 Paired Recommendations 1 International Standards equivalent in technical content.
2
2.3 Additional references .
2
.........................................................................................................
3 General considerations
3
...................................................
3.1 Compatibility with versions of Recommendation X.25
5
3.2 Environments .
5
.........................................................
33 Differences in DTF$DTE and DTE/DCE operation
6
...................................................................
3.4 Operation over circuit-switched connections
6
.............................................................................
3.5 Provision of the OS1 Network Service
7
3.6 External Packet Layer interactions .
7
..............................................................................................................
3.7 Logical channels
8
..........................................................................................................
3.8 Packet Layer entity
8
.....................................................................................................................
3.9 Packet types
8
...........................................................................................
3.10 Procedures for initialization
10
..........................................................................................................
4 Procedures for restart
10
.............................................................................................
4.1 Originating a restart request
12
...........................................................................................
4.2 Receiving a restart indication
12
...............................................................................................................
4.3 Restart collision
12
........................................................................................................
4.4 Restart confirmation
12
.................................................................
4.5 Determining “DTE” or “DCE” characteristics
13
..................................................................
5 Procedures for Virtual Call setup and clearing
13
......................................................................................................................
5.1 Ready state
13
.....................................................................................
5.2 Procedures for Virtual Call setup
16
................................................................................................................
5.3 Rejecting a call
16
.....................................................................................................
5.4 Aborting a call request
16
................................................................................
5.5 Procedures for Virtual Call clearing
s . 17
.......................................................................
6 Procedures for data and interrupt transfer
17
................................................................................
6.1 States for data and interrupt transfer
17
.......................................................
6.2 Maximum User Data Field length of DATA packets
18
................................................................................................
6.3 Delivery Confirmation bit
18
...............................................................................................................
6.4 More Data mark
18
...............................................................................................
6.5 Complete packet sequence
20
.....................................................................................................................
6.6 Qualifier bit
21
....................................................................
6.7 Fragmentation and reassembly of messages
21
...................................................................................................
6.8 Procedures for interrupt
22
.......................................................................................
6.9 Transit delay of DATA packets
22
..................................................................................................
7 Procedures for flow control
22
7.1 Flow control .
26
..........................................................
7.2 Throughput characteristics and throughput classes
.............................................................................................................. 26
8 Procedures for reset
27
...............................................................................................
8.1 Originating a reset request
o ISO/IEC 1995
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ii
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0 ISO/IEC ISO/IEC 8208:1995(E)
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
. . .o.o.oo.o.*o.o*o.o.o.ee.e. 29
10 Effects of Layers 1 and 2 on the Packet Layer
..
H 29
11 Error handiing . e. .
30
11.1 The DIAGNOSTIC packet .
30
11.2 Nonreceipt of window-rotation information .
31
113 Receipt of erroneous DATA packets .
32
12 Packet formats
......................................................................................................................
32
12.1 General .
33
12.2 Call setup and call clearing packets .
41
123 DATA and interrupt packets .
42
12.4 Flow control packets .
44
12.5 Reset packets .
44
12.6 Restart packets .
46
...................................................................................................
12.7 DIAGNOSTIC packet
47
12.8 REJECT packet .
48
12.9 Registration packets .
49
13 Procedures for optional user facilities .
49
13.1 On-line Facility Registration .
57
13.2 Extended Packet Sequence Numbering .
57
133 D-bit Modification. .
57
13.4 Packet Retransmission .
58
13.5 Incoming Calls Barred .
58
13.6 Outgoing Calls Barred .
.............................................................................. 59
13.7 One-way Logical Channel Outgoing
............................................................................. 59
13.8 One-way Logical Channel Incoming
59
13.9 Nonstandard Default Packet Sizes .
............................................................................ 59
13.10 Nonstandard Default Window Sizes
..................................................................... 59
13.11 Default Throughput Classes Assignment
........................................................................... 59
13.12 Flow Control Parameter Negotiation
61
.....................................................................................
13.13 Throughput Class Negotiation
63
............................................................................
13.14 Closed User Group related facilities
67
..............................................................
13.15 Bilateral Closed User Group related facilities
67
...................................................................................................................
13.16 Fast Select
68
................................................................................................
13.17 Fast Select Acceptance
68
........................................................................................................
13.18 Reverse Charging
68
.....................................................................................
13.19 Reverse Charging Acceptance
69
13.20 Local Charging Prevention .
69
13.21 Network User Identification (NUI) related facilities .
70
13.22 Charging Information .
71
13.23 ROA related facilities .
71
13.24 Hunt Group .
................................................. 72
13.25 Call Redirection and Call Deflection related facilities
................................................................. 74
13.26 Called Line Address Modified Notification
74
13.27 Transit Delay Selection and Indication .
...................................................................... 74
13.28 Alternative Addressing related facilities
76
13.29 Reference Number .
78
.....................................................
14 Procedures for optional IT&T specified DTE facilities
............................................................................................. 78
14.1 Calling Address Extension
78
14.2 Called Address Extension .
. . .
111
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ISO/IEC8208:1995(E)
o ISO/IEC
143 Minimum Throughput Class Negotiation . 78
78
14.4 End-to-End Transit Delay Negotiation .
79
14.5 Priority .
14.6 Protection . 79
14.7 Expedited Data Negotiation . 79
15 Format for Facility Field in call setup/clearing packets . 79
15.1 General . 79
15.2 Coding of the Facility Field for optional user facilities . 81
87
153 Coding of the Facility Field for ITU-T specified DTE facilities .
90
16 Format for Registration Field in registration packets .
16.1 General . 90
16.2 Coding of the Registration Field for registration-facilities . 90
93
17 Diagnostic codes .
100
18 Timers and retransmission counts .
19 . 104
State diagrams
110
20 State tables .
120
21 Conformance .
21.1 static conformance . 120
21.2 Protocol Implementation Conformance Statement . 120
213 Dynamic conformance . 120
Annexes
123
A Private networks .
132
B PICS Proforma .
160
C Differences between various editions of ISO/IEC 8208 .
169
D Abbreviations .
iv
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o ISO/IEC ISO/IEC8208:1995(E)
Foreword
IS0 (the International Organization for Standardization) and IEC (the Inter-
national 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 organization 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 8208 was prepared by Joint Technical Committee
ISO/IEC JTC 1, Information technology, Subcommittee SC 6, Telecommuni-
cations and information exchange between systems.
This third edition cancels and replaces the second edition (ISOLIEC 8208:1990),
which has been technically revised. It also incorporates amendment 1: 1990,
amendment 3 : 199 1 and technical corrigendum 1: 1992.
Annexes A and B form an integral part of this International Standard. Annexes C
and D are for information only.
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INTERNATIONAL STANDARD o ISO/IEiC ISO/IEC 8208:1995(E)
Information technology - Data communications -
X.25 Packet Layer Protocol for Data Terminal Equipment
1 Scope scope. This International Standard contains the specifications
that ITU-T Recommendation X.25 places on DTEs. In addition,
This International Standard specifies the procedures, formats and
this International Standard contains added specifications to
facilities at the Packet Layer for Data Terminal Equipment
facilitate interworking between DTEs and to cover direct DTE-
(DTE) operating in conformance with ITU-T Recommendation
to-DTE operation. This broader scope has to be recognized in
X,25. Both Virtual Call and Permanent Virtual Circuit modes of
the application of this International Standard.
operation are covered.
The Packet Layer protocol specified herein can be used in both 2 Normative references
Open Systems Interconnection (OSI) and non-OS1 environments.
standards and recommendations contain
The following
When used within the context of OSI, the Packet Layer protocol
through reference in this text, constitute
provisions which,
is encompassed in the Network Layer of the OS1 Reference
provisions of this International Standard. At the time of
Model, ITU-T Rec. X.200 1 ISO/IEC 7498-l.
publication, the editions indicated were valid. All standards and
This International Standard covers DTE operation at the Packet recommendations are subject to revision, and parties to
Layer when accessing a public or private packet-switched agreements based on this International Standard are encouraged
network conforming to ITU-T Recommendation X.25 by means to investigate the possibility of applying the most recent editions
of a dedicated path or a circuit-switched connection. It also of the standards and recommendations listed below. Members of
covers the additional Packet Layer procedures necessary for two IEC and IS0 maintain registers of currently valid International
DTEs conforming to this International Standard to communicate Standards. The Telecommunication Standardization Bureau of
directly (i.e., without an intervening packet-switched network) the ITU maintains a register of currently valid ITU-T
over a dedicated path, a circuit-switched connection, or a local Recommendations.
area network (LAN).
2.1 Identical Recommendations 1 International
Standards
This International Standard also covers private networks that use
ITU-T Recommendation X.25 to connect to packet-switched
ITU-T Recommendation X.200 (1994) 1 ISOAEC 7498-l : 1994,
public data networks and that may also offer an X.25 interface to
Information technology - Open Systems Interconnection -
a DTE (see annex A).
Basic Reference Model: The Basic Model
To evaluate conformance of a particular implementation, it is
CCI’IT Recommendation X.213 (1992) 1 ISO/IEC 8348 : 1993,
necessary to have a statement of which capabilities and options
Open Systems Interconnection -
Information technology -
have been implemented. Such a statement is called a Protocol
Network Service Definition
Implementation Conformance Statement (PICS), as defined in
ITU-T Recommendation X.273 (1994) 1 ISO5EC 11577 : 1995,
ITU-T Rec. X.290 1 ISOAEC 9646-l. Annex B provides the
Information technology - Open Systems Interconnection -
PICS proforma in accordance with the relevant guidance given in
Network layer security protocol
ITU-T Rec. X.296 I ISO/IEC 9646-7.
CCI’IT Recommendation X.612 (1992) I ISO/IEC 9574 : 1992,
The first edition of this International Standard was based on the
Information technology - Provision of the OSI connection-mode
1984 CCITI’ Red Book text of Recommendation X.25. It also
network service by packet-mode terminal equipment connected to
contained the necessary provisions for compatibility with the
earlier 1980 CCITT Yellow Book text of Recommendation X.25. an integrated services digital network (ISDN)
The second edition was based on the 1988 CCI’IT Blue Book
CCITI’ Recommendation X.613 (1992) I ISO/IEC 10588 : 1993,
text of Recommendation X.25. This third edition is based upon
Information technology - Use of X.25 Packet Layer Protocol in
the 1993 version of X.25. Retained within this third edition are
conjunction with X.2lK.21bis to provide the OSI connection-
the
necessary provisions for compatibility with the 1988, 1984
mode Network Service
and
1980 versions of X.25. The differences between the first,
second and third editions of this International Standard are CCI’IT Recommendation X.614 (1992) I ISO/IEC 10732: 1993,
summarized in annex C. Information technology - Use of X.25 Packet Layer Protocol to
provide the OSI connection-mode Network Service over the
It should be noted that this International Standard and ITU-T
telephone network
Recommendation X.25 as it applies to DTEs are different in
1
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ISO/IEC 8208 : 1995(E) 0 ISO/IEC
2.2 Paired Recommendations 1 International
another PAD
Standards equivalent in technical content
ITU-T Recommendation X.31 (1993), Support of packet mode
- CCI’IT Recommendation T.50 (1992), International Reference temzinal equipment by an ISDN
Alphabet (IRA)
ITU-T Recommendation X.32 (1993), Interface between data
ISO/IEC 646 : 1991, Information technology - IS0 7-bit
terminal equipment (DTE) and data circuit-terminating
coded character set for information interchange equipment (DCE) for terminals operating in the packet mode and
clccessing a packet switched public data network through a
- CCITI’ Recommendation X.212 (1988), Data link service
public switched telephone network or an integrated services
dejinition for open systems interconnection for CCIZT
digital network or a circuit switched public data network
applications
ITU-T Recommendation X.96 (1993), Call progress signals in
ISO/IEC
8886 : 1992, Information technology -
public data networks
Telecommunications and information exchange between
systems ITU-T Recommendation X. 121 (1993), International numbering
- Data link service definition for Open Systems
Interconnection plan forpublic data networks
- ITU-T Recommendation X.223 (1993), Use of X.25 to provide CCI’IT Recommendation X.244 (1988), Procedure for the
virtual call
the OSI connection-mode network service for ITU-T exchange of protocol identification during
applications establishment on packet switchedpublic data networks
ISO/IEC Information technology - CCITT Recommendation X.610 (1992), Provision and support of
8878 : 1992,
Telecommunications and information exchange between the OSI connection-mode network service
systems - Use of X.25 to provide the OSI Connection-mode
ISO/IEC 7776 : 1994, Information technology -
Network Service
Telecommunications and information exchange between systems
- ITU-T Recommendation X.290 (1995), OSI conformance - High-level data link control procedures - Description of the
testing methodology and framework for protocol X.25 IAPB-compatible DTE data link procedures
Recommendations for ITU-T applications - General concepts
ISO/IEC 8881 : 1989, Information processing systems - Data
Use of the X.25 packet level protocol in local
ISOIIEC 9646-1 : 1995, Information technology - Open communications -
Systems Interconnection - Conformance testing methodology area networks
and framework - Part 1: General concepts
ISO/IEC TR 10029 : 1989, Information technology -
- ITU-T Recommendation X.296 (1995), OSI conformance Telecommunications and information exchange between systems
testing methodology and framework for protocol - Operation of an X.25 interworking unit
Recommendations for ITU-T applications - Implementation
ISO/IEC 10039: 199 1, Information technology - Open Systems
Conformance Statements
Local area networks - Medium Access
Interconnection -
ISOIIEC 9646-7 : 1995, Information technology - Open Control (MAC) service definition
Systems Interconnection - Conformance testing methodology
ISO/IEC TR 13532:-l), Information technology -
and framework - Part 7: Implementation Conformance
Telecommunications and information exchange between systems
Statements
- Protocol combinations to provide and support the OSI
network service
2.3 Additional references
CCI’IT Recommendation D.12 (1988), Measurement unit for RFC 1166, Internet numbers, July 1990.
charging by volume in the international packet-switched data
communication service 3 General considerations
ITU-T Recommendation X.2 (1993), International data This International Standard defines, from the viewpoint of a
transmission services and optional user facilities in public data DTE, the Packet Layer, which governs the transfer of packets at a
networks and ISDNs DTE/DCE or DTE/DTE interface.2) On the transmitting side, the
Packet Layer in a sending DTE performs the basic function of
ITU-T Recommendation X.25 (1993), Interface between data
packetizing messages delivered by a higher layer entity in the
terminal equipment (DTE) and data circuit-terminating
same DTE before giving the information to the Data Link Layer
equipment (DCE) for terminals operating in the packet mode and
for transmission to a DXE. On the receiving side, the Packet
connected to public data networks by dedicated circuit
Layer in a DTE performs the basic functions of receiving packets
from the Data Link Layer, checking packets for correctness,
ITU-T Recommendation X.29 (1993), Procedures for the
stripping off packet headers, and formulating messages from the
exchange of control information and user data between a packet
assembly/disassembly (PAD) facility and a packet mode DTE or
1) To be published.
where it would not matter whether a DTE or a DCE was being referred to. Therefore, this International
2) The term “DXE” is used in those contexts
Standard can be viewed as defining the Packet Layer at the DTE/DXE interface.
2
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0 1s0/IIx
ISO/IEC 8208 : 1995(E)
packetized user data and passing them to a higher layer entity in b) a negligible out-of-sequence rate; and
the DTE.
c) a negligible packet-loss and duplication rate.
This International Standard presents a description of the Packet
The Packet Layer provides the following functional capabilities
Layer for “Virtual Call” service and “Permanent Virtual Circuit”
that facilitate reliable and efficient data communications:
service.
a) multiplexing - the ability to support multiple
The following information is presented:
communications;
general considerations (clause 3);
a>
b) data transfer - the ability to send and receive data;
procedures for exchanging packets across a DTE/DXE
W
c) flow control - the ability to control the flow of data;
interface (clauses 4 through 11). Clause 5 applies to the
setup and clearing procedures for Virtual Call service, d) interrupt transfer - the ability to send and receive a
while the other clauses apply to both Virtual Call service small amount of information independent of the data
and Permanent Virtual Circuit service; stream;
packet formats (clause 12); e) error control - the ability to detect Packet Layer errors;
4
procedures for optional user facilities that may be f) reset and restart - the ability to reinitialize
4
available on a DTE/DXE interface (clauses 13 and 14); communication paths in the event that Packet Layer
errors are encountered.
formats for optional user facilities and registration-
e>
facilities (c
...
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