ISO/IEC 8208:1995

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

General Information

• Status: Withdrawn
• Publication Date: 26-Jul-1995
• Withdrawal Date: 26-Jul-1995
• ICS: 35.100.30 - Network layer
• Technical Committee: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
• Drafting Committee: ISO/IEC JTC 1/SC 6/WG 7 - Network, transport and future network
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 16-Nov-2000
• Completion Date: 30-Oct-2025

Relations

• Consolidated By: ISO/TS 24530-1:2006 - Traffic and Travel Information (TTI) - TTI via Transport Protocol Experts Group (TPEG) Extensible Markup Language (XML) - Part 1: Introduction, common data types and tpegML
• Effective Date: 06-Jun-2022
• Revises: ISO/IEC 8208:1990/Amd 3:1991 - Information technology - Data communications - X.25 Packet Layer Protocol for Data Terminal Equipment - Amendment 3
• Effective Date: 16-Oct-2025
• Revises: ISO/IEC 8208:1990/Amd 1:1990 - Information technology - Data communications - X.25 Packet Layer Protocol for Data Terminal Equipment - Amendment 1
• Effective Date: 16-Oct-2025
• Revised: ISO/IEC 8208:2000 - Information technology - Data communications - X.25 Packet Layer Protocol for Data Terminal Equipment
• Effective Date: 15-Apr-2008
• Revises: ISO/IEC 8208:1990 - Information technology - Data communications - X.25 Packet Layer Protocol for Data Terminal Equipment
• Effective Date: 15-Apr-2008

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)
ISO/IEC 8208: 1995(E)
CONTENTS
Scope . . . . . . . . . . . . .*.~.~.
...........................................................................................................
2 Normative references.
....................................................
2.1 Identical Recommendations 1 International Standards
..... 2
2.2 Paired Recommendations 1 International Standards equivalent in technical content.
2.3 Additional references .
.........................................................................................................
3 General considerations
...................................................
3.1 Compatibility with versions of Recommendation X.25
3.2 Environments .
.........................................................
33 Differences in DTF$DTE and DTE/DCE operation
...................................................................
3.4 Operation over circuit-switched connections
.............................................................................
3.5 Provision of the OS1 Network Service
3.6 External Packet Layer interactions .
..............................................................................................................
3.7 Logical channels
..........................................................................................................
3.8 Packet Layer entity
.....................................................................................................................
3.9 Packet types
...........................................................................................
3.10 Procedures for initialization
..........................................................................................................
4 Procedures for restart
.............................................................................................
4.1 Originating a restart request
...........................................................................................
4.2 Receiving a restart indication
...............................................................................................................
4.3 Restart collision
........................................................................................................
4.4 Restart confirmation
.................................................................
4.5 Determining “DTE” or “DCE” characteristics
..................................................................
5 Procedures for Virtual Call setup and clearing
......................................................................................................................
5.1 Ready state
.....................................................................................
5.2 Procedures for Virtual Call setup
................................................................................................................
5.3 Rejecting a call
.....................................................................................................
5.4 Aborting a call request
................................................................................
5.5 Procedures for Virtual Call clearing
s . 17
.......................................................................
6 Procedures for data and interrupt transfer
................................................................................
6.1 States for data and interrupt transfer
.......................................................
6.2 Maximum User Data Field length of DATA packets
................................................................................................
6.3 Delivery Confirmation bit
...............................................................................................................
6.4 More Data mark
...............................................................................................
6.5 Complete packet sequence
.....................................................................................................................
6.6 Qualifier bit
....................................................................
6.7 Fragmentation and reassembly of messages
...................................................................................................
6.8 Procedures for interrupt
.......................................................................................
6.9 Transit delay of DATA packets
..................................................................................................
7 Procedures for flow control
7.1 Flow control .
..........................................................
7.2 Throughput characteristics and throughput classes
.............................................................................................................. 26
8 Procedures for reset
...............................................................................................
8.1 Originating a reset request
o ISO/IEC 1995
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photocopying and microfilm, without permission in writing from the publisher.
ISO/IEC Copyright Office l Case postale 56 l CII- 1211 @en&e 20 l Switzerland
Printed in Switzerland
ii
0 ISO/IEC ISO/IEC 8208:1995(E)
8.2 Receiving a reset indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3 Reset collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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. .
11.1 The DIAGNOSTIC packet .
11.2 Nonreceipt of window-rotation information .
113 Receipt of erroneous DATA packets .
12 Packet formats
......................................................................................................................
12.1 General .
12.2 Call setup and call clearing packets .
123 DATA and interrupt packets .
12.4 Flow control packets .
12.5 Reset packets .
12.6 Restart packets .
...................................................................................................
12.7 DIAGNOSTIC packet
12.8 REJECT packet .
12.9 Registration packets .
13 Procedures for optional user facilities .
13.1 On-line Facility Registration .
13.2 Extended Packet Sequence Numbering .
133 D-bit Modification. .
13.4 Packet Retransmission .
13.5 Incoming Calls Barred .
13.6 Outgoing Calls Barred .
.............................................................................. 59
13.7 One-way Logical Channel Outgoing
............................................................................. 59
13.8 One-way Logical Channel Incoming
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
.....................................................................................
13.13 Throughput Class Negotiation
............................................................................
13.14 Closed User Group related facilities
..............................................................
13.15 Bilateral Closed User Group related facilities
...................................................................................................................
13.16 Fast Select
................................................................................................
13.17 Fast Select Acceptance
........................................................................................................
13.18 Reverse Charging
.....................................................................................
13.19 Reverse Charging Acceptance
13.20 Local Charging Prevention .
13.21 Network User Identification (NUI) related facilities .
13.22 Charging Information .
13.23 ROA related facilities .
13.24 Hunt Group .
................................................. 72
13.25 Call Redirection and Call Deflection related facilities
................................................................. 74
13.26 Called Line Address Modified Notification
13.27 Transit Delay Selection and Indication .
...................................................................... 74
13.28 Alternative Addressing related facilities
13.29 Reference Number .
.....................................................
14 Procedures for optional IT&T specified DTE facilities
............................................................................................. 78
14.1 Calling Address Extension
14.2 Called Address Extension .
. . .
ISO/IEC8208:1995(E)
o ISO/IEC
143 Minimum Throughput Class Negotiation . 78
14.4 End-to-End Transit Delay Negotiation .
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
153 Coding of the Facility Field for ITU-T specified DTE facilities .
16 Format for Registration Field in registration packets .
16.1 General . 90
16.2 Coding of the Registration Field for registration-facilities . 90
17 Diagnostic codes .
18 Timers and retransmission counts .
19 . 104
State diagrams
20 State tables .
21 Conformance .
21.1 static conformance . 120
21.2 Protocol Implementation Conformance Statement . 120
213 Dynamic conformance . 120
Annexes
A Private networks .
B PICS Proforma .
C Differences between various editions of ISO/IEC 8208 .
D Abbreviations .
iv
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
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.
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;
procedures for optional user facilities that may be f) reset and restart - the ability to reinitialize
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 (clauses 15 and 16, respectively); A number of design principles were used in the formulation of
the Packet Layer procedures for DTEs specified in this
coding of the Diagnostic Code Field (clause 17);
f>
International Standard:
timers and retransmission counts (clause 18);
g)
conform fully to Recommendation X.25 for operation
state diagrams and state tables (clauses 19 and 20, with a packet-switched network;
h)
respectively);
minimize the differences between operating with a
W
conformance requirements (clause 21); packet-switched network and operating directly with
another DTE;
applications of this International Standard to private
j>
networks that connect to a packet-switched public data provide, where possible, the opportunity for recovery
from an error condition without incurring data loss at the
network and that may also offer an X.25 interface to a
DTE (annex A); and Packet Layer;
the PICS proforma (annex B). align the services provided by the Packet Layer with the
k) d)
Network Layer services defined for Open Systems
To facilitate comprehension of this International Standard, a
Interconnection; and
number of conventions have been adopted in the presentation of
the text: generally follow the organization of text in
e>
Recommendation X.25.
the names of states and packets are in full capitals;
a>
3.1 Compatibility with versions of Recommendation
the names of the optional user facilities, packet fields,
b)
x.25
causes and diagnostics are in initial capitals;
The Packet Layer procedures and formats specified in this
italicized text is used to denote differences between
International Standard are compatible with the 1993 version of
Virtual Call and Permanent Virtual Circuit service and
Recommendation X.25.
between DTE/DTE and DTIYDCE interfaces (entire
NOTE - The TOA/NPI Address Subscription Facility along with
clauses or subclauses that pertain to one service or to
associated addressing procedures and formats, introduced into the 1988
one interface type are not italicized; the appropriate
version and further elaborated in the 1993 version of Recommendation
environment is denoted at the beginning of the clause or
X.25, is not included in this International Standard since the ITU-T has
subclause);
continued its designation for further study.
terms not explicitly defined within this International
For DTEs needing to operate with the earlier versions of
Standard are taken from the referenced ITU-T X-series
Recommendation X.25, the following restrictions apply.
recommendations.
3.1.1 Limitations for compatibility with X.25-1988
abbreviations are listed in Annex D.
e>
For DTEs needing to operate with the 1988 (Blue Book) version
The Packet Layer procedures in this International Standard are
of Recommendation X.25, the following 1993 capabilities are not
based on an underlying service (for example, that provided by
used:
ISO/IEC 7776 or, more generally, the provision of the OS1 Data
Link Service defined in CCI’IT Rec. X.212 1 ISO/IEC 8886) that a) expanded format of the Address Fields; for 1988
provides: operaion, only the Address Block with the A-bit = 0 is
permitted (see 12.2);
a) a negligible residual-bit-error rate;
ISOnEC 8208 : 1995(E)
0 ISO/IEC
b) Facility Fields in CALL REQUEST, INCOMING CALL, b) the following CCITT-specified DTE facilities
CALL ACCEPTED, CALL CONNECTED, CLEAR
- Priority (see 14. 5)9 and
REQUEST, CLEAR INDICATION, and CLEAR
CONFIRMATION, packets with a length from 109 to - Protection (see 14.6);
255 octets (see P2.22, 12.2.3.P, 12.2.4.1, 12.2.5.2 and
for 1984 operation, the above fmilities were not defined;
12.2.6.2); for 1988 operation, thiscfield is limited to IO9
octets. coding of the following CCITT-specicfied DTE facilities
were modified
c) the following optional user facilities
- Calling Address Extension (see 15.3.2.1), and
- Alternative Addressing relatedfacilities (see 13.28);
- Called Address Extension (see 15.3.2.2);
for 1988 operation, these facilities were not defined;
for 1984 operation, only BCD encoding of the addresses
expanded capabilities for the following optional user
is permitted; and
facilities
d) the throughput class of 64 000 bit/s; for 1984 operation
- Throughput Class Negotiation facilities (see 13.13),
the largest throughput class is 48 000 bit/s.
and
3J.3 Limitations for compatibility with X.25-1980
- Call Redirection and Call Deflection related
facilities (see 13.25);
For DTEs needing to operate with the 1980 (Yellow Book)
version of Recommendation X.25, the following 1984
for 1988 operation, the Extended Throughput Class
capabilities are not used in addition to those cited in 3.1.2:
I
Negotiation Facility and the Inter-network Call
Redirection and Deflection (ICRD) control facilities a maximum User Data Field lengths in DATA packets of
,>
were not deBned; 2 048 and 4 096 octets (see 6.2); for 1980 operation, the
largest maximum User Data Field length allowed is
coding of the following CCITT-specified DTE facilities
1024 octets;
(renamed WV-T specified DTE facilities” in the 1993
version of Recommendation X.25) were modified b Facility Fields in CALL REQUEST INCOMING CALL,
>
CALL ACCEPTED, and CALL CONNECTED packets
- Minimum Throughput Class Negotiation (see
with a length from 64 to 109 octets (see 12.2.3.1 and
15.3.2.3);
12.2.4.1); for 1980 operation, this field is limited to 63
for 1988 operation, only the basic format existed; and octets and bit 7 of the Facility Length Field shall be set
to 0;
f) the throughput classes of 128 000 bit/s and 192 000 bit/s
(in the basic format) and throughput classes from cause codes with bit 8 set to one in CLEAR
6)
256 000 bit/s up to, and including, 2 048 000 bit/s (in the RESET
REQUEST/INDICATION,
extended format); for 1988 operation, the largest and
REQUEST/INDICATION, RESTART
throughput class is 64 000 bit/s.
REQUEST/INDICATION packets (see 12.2.5.1.1,
12.5.1.1, and 12.6.1.1, respectively); for 1980 operation,
It should also be noted that the term “RPOA” meaning
this bit shall be set to zero;
Recognized Private Operating Agency used in 1988 and earlier
versions of Recommendation X.25 has been replaced by the term
nonzero Address Length and Facility Length Fields in
d)
“ROB” meaning Recognized Operating Agency in the 1993
CLEAR REQUEST and CLEAR INDICATION packets
version of Recommendation X.25.
(see 12.2.5.2); for 1980 operation, these length fields
shall indicate zero octets and may only be present when
3.1.2 Limitations for compatibility with X.25-1984
the packet contains a Clear User Data Field;
For DTEs needing to operate with the 1984 (Red Book) version
the extended format for CLEAR CONFIRMATION
of Recommendation X.25, the following 1988 capabilities are not
packets (see 12.2.6.2); for 1980 operation, only the
used in addition to those cited in 3.1 .l:
basic format may be used;
a) expanded capabilities for the following optional user
Interrupt User Data Fields in INTERRUPT packets
f>
facilities
containing from two to 32 octets (see 12.3.2); for 1980
- Network User Identification (NW) related facilities
operation, this field shall contain exactly one octet;
(see 13.21),
the following optional user facilities:
g>
- RPOA related facilities (see 13.23), and
- On-line Facility Registration (see 13.1),
- Call Redirection and Call Deflection related
- Local Charging Prevention (see 13.20),
facilities (see 13.25);
- Network User Identification (see 13.21),
for 1984 opertiion, Call Deflection and NUI Override
were not defined and the NUI and RPOA facilities were - Charging Information (see 13.22),
not explicitly
separated into subscription and
- Hunt Group (see 13.24),
negotiation facilities:
0 ISO/IEC ISOlIEC 8208 : 1995(E)
- Call Redirection and Call DeJection Notification NOTES
(see 13.25),
1 The situation where the “DTE” is a private network accessing
a public network DCE is covered in annex A.
- Called Line Address Modified Notijcation (see
13.26), and
2 The DCE may be a packet-switched data network operating
in accordance with Recommendation X.25 or a packet handler
- Transit Delay Selection and Indication (see 13.27);
capability in an ISDN operating in accordance with
Recommendation X.3 1.
for 1980 operation, the above facilities cannot be used;
h) expanded capabilities for the following optional user
b) DTE/DTE operation:
facilities:
- DTE-to-DTF operation over a leased line (data
- Closed User Groups (CUG): subscription to the
network, ISDN or telephone network),
Closed User Group With Outgoing and/or Incoming
- DTE-to-DTE operation over a circuit-switched
Access Facilities without a preferential CUG (see
connection (circuit-switched data network, circuit-
13.14.2 and 13J4.3, respectively), use of the
switched capability of an ISDN, or the switched
extended format of the CUG Selection Facility for
telephone network). Additional considerations are
indicating membership in more than 100 CUGs (see
given in 3.4,
13.14.6), and the use of the Closed User Group With
Outgoing Access (CUG/OA) Selection Facility (see
- DTE-to-DTE operation over a Eocal Area Network
13.14.7); for 1980 operation, all CUG subscriptions
(LAN). The provisions of ISO/IEC 8881 apply.
shall specify a preferential CUG, only the basic
NOTE 3 - The situation where a “DTE” is a gateway on
format of the CUG Selection Facility is allowed for
the LAN to other networks is covered in annex A.
indicating membership in 100 or less CUGs, and the
CUG/OA Selection Facility cannot be used,
Differences between DTE/DCE and DTE/DTE operation are
enumerated in 3.3.
- Fast Select and Fast Select Acceptance (see 13.16
and 13.17, respectively): inclusion of a Clear User
3.3 Differences in DTE/DTE and DTE/DCE operation
Data Field in CLEAR REQUEST and CLEAR
For the most part, much of the Packet Layer protocol described
INDICATION packets after call setup has been
herein is independent of whether the DTE is connected to a DCE
completed; for 1980 operation, the above packets
(e.g., X.25 network environment) or directly to another DTE.
can contain a Clear User Data Field only when sent
However, there are certain procedures within Recommendation
or received in direct response to an INCOMING
X.25 that are not mandatory of a DTE but are required in a
CALL or a CALL REQUEST packet, respectively,
DTE/DTE environment. To minimize the number of differences
and
that arise when considering whether connection is to a DCE or to
- RPOA Selection (see 13.23): use of the extended
another DTE, the following procedures are always required of a
format of the RPOA Selection Facility to select one
DTE:
or more RPOAs, and agreement for a period of time
the Address Length Fields and the Facility Length Field
a>
with the DCE to a set of RPOAs to pertain to all
shall be supplied in CALL ACCEPTED packets even tf
CALL REQUEST packets; for 1980 operation, a
they indicate that no address and facility inforsnation,
DTE wishing to select an RPOA can only do so in a
respectively, are present;
CXLL REQUEST packet and can only use the basic
the Diagnostic Code Field in RESTART REQUEST,
b)
fomat of the RPOA Selection Facility to select a
CLEAR REQUEST, and RESET REQUEST packets
single RPOA; and
shall be supplied even if it indicates “No Additional
i) the CCITT-specified DTE facilities and the associated
Information” (that is, although specific diagnostics are
facility marker (see clause 14 and 15.1, respectively);
defined for particular error situations, a DTE may use
for 1980 operation, these facilities and the marker
more general codes as discussed in note 1 of table 25);
cannot be used.
a DATA packet whose User Data Field is less than the
C>
3.2 Environments
maximum allowed and which has its D-bit set to 0 and
M-bit set to 1 shall not be transmitted; and
The DTE aspects of the Packet Layer protocol set forth in this
upon notification that the Data Link Layer has
International Standard are applicable to a number of d)
completed its initialization procedures or that it has
environments including:
recovered from a failure in which the Data Link Layer
a) DTE/DCE operation:
was in the disconnected phase, the DTE shall transmit a
RESTART REQUEST packet across the DTE/DXE
- DTE access to a DCE via a dedicated path,
interface.
- DTE access to a DCE via a circuit-switched
connection (circuit-switched data network, circuit-
However, for a few of the procedures described in the following
switched capability of an Integrated Services Digital
clauses, consideration shall be given to whether the DTE is
Network (ISDN), or the switched telephone
connected to a DCE or another DTE. For a DTE/DTE
network). Additional considerations are given in
environment, these considerations are listed below.
3.4.
ISO/IEC 8208 : 1995(E) 0 ISO/IEC
One of the DTEs shall act as a DCEfor
i) A called DTE which subscribes to the Flow Control
Parameter Negotiation Facility (see 13.12) and/or one
- logical channel selection during Virtual Call setup
of the Throughput Class Negotiation facilities (see
(see figure I),
13.13) will not receive, in an INCOMING CALL packet,
- resolution of Virtual Call collision (see 52.5).
a facility indication from which to negotiate if the
NOTE - This does not apply if the Reference Number
calling DTE is satisfied with the default values and, thus,
Facility is used.
has not included the facility request in its CALL
(The choice is made independently for each of the DTE’s REQUESTpacket. In a similar manner, a calling DTE
Packet Layer entities; see 3.8.) which subscribes to these facilities will not receive, in a
CALL CONNECTED packet, a facility indication if the
The restart procedure (see 4.5) may be used to
called DTE is satis$ed with the values in the
determine which DTE acts as a DCE and which DTE
INCOMING CALL packet and, thus, has not included a
maintains its role as a DTE with respect to the above
facility request in its CALL ACCEPTED packet. (In a
items. (The procedures in 4.5 may be used in the
DTE/z)CE environment, these facility indications are
general case of a DTIYDXE interface via a dedicated
always present if the DTE has subscribed to these
path or a circuit-switched connection. Alternatively, if a
facilities. )
DTE is to operate only in a DTE/DCE environment or a
DTEYDTE environment where, by administration, the
3.4 Operation over circuit-switched connections
roles can be predetermined and fixed, then the DTE may
When communications between a DTE and DXE involves a
be initialized to act appropriately.)
circuit-switched connection (e.g., through a circuit-switched data
A DTE shall be able to
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