ISO/IEC 8208:1990
(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
Second edition
1990-03-1 5
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 : 1990 (E)
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.
ISOAEC 8208 : 1990 (E)
Page
CONTENTS
V
Foreword .
1
1 Scope .
1
2 Normative references .
2
3 General considerations .
3
3.1 Compatibility with versions of CClTï Recommendation X.25 .
4
3.2 Environments .
33 Differences in DTE/DTE and DTE/DCE operation . 4
5
3.4 Operation over circuit-switched connections .
6
3.5 Provision of the OS1 Network Service .
6
3.6 External Packet Layer interactions .
6
3.7 Logical channels .
6
3.8 Packet Layer entity .
3.9 Packet types . 7
7
3.10 Procedures for initialization .
4 Procedures for restart . 9
4.1 Originating a restart request . 9
4.2 Receiving a restart indication . 11
43 Restart collision . 11
4.4 Restart confirmation . 11
Determining “DTE or “DCE characteristics . 11
45
5 Procedures for Virtual Call setup and clearing . 12
5.1 Ready state . 12
5.2 Proc+Ves for Vial Call setup . . . : . 12
5.3 . Rejecting a call . : . . 15
5.4 Aborting a call request . 15
Procedures for Virtual Call clearing . 15
55
6 Procedures for data and interrupt transfer . 16
16
6.1 States for data and interrupt transfer .
6.2 Maximum User Data Field length of DATA packets . 17
63 Delivery Confirmation bit . 17
17
6.4 More Data mark .
19
65 Complete packet sequence .
20
6.6 Qualifier bit .
6.7 Fragmentation and reassembly of messages . 20
20
68 Procedures for interrupt .
6.9 Transit delay of DATA packets . 22
*
Q ISO/IEC 1990
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7 Procedures for flow control . 22
7.1 Flow control . 22
7.2 Throughput characteristics and throughput classes . 25
8 Procedures for reset . 26
8.1 Originating a reset request . 26
8.2 Receiving a reset indication . 26
83 Reset collision . 28
8.4 Reset confirmation . 28
9 Effects of clear, reset, and restart procedures on the transfer of packets . 28
10 Effects of Layers 1 and 2 on the Packet Layer . 28
11 Error handling . 29
11.1 The DIAGNOSTIC packet . 29
11.2 Nonreceipt of window-rotation information . 30
113 Receipt of erroneous DATA packets . 31
12 Packet formats . 31
12.1 General . 31
12.2 Call setup and call clearing packets . 33
123 DATA and interrupt packets . 40
12.4 Flow control packets . 41
12.5 Reset packets . 42
12.6 Restart packets . 44
12.7 DIAGNOSTIC packet . 45
12.8 REJECT packet . 46
12.9 Registration packets . 47
13 Procedures for optional user facilities . 48
13.1 On-line Facility Registration . 48
13.2 Extended Packet Sequence Numbering . 56
133 D-bit Modification . 56
13.4 Packet Retransmission . 57
13.5 Incoming Calls Barred . 58
13.6 Outgoing Calls Barred . 58
13.7 One-way Logical Channel Outgoing . 58
13.8 One-way Logical Channel Incoming . 58
13.9 Nonstandard Default Packet Sizes . 58
13.10 Nonstandard Default Window Sizes . 58
13.11 Default Throughput Classes Assignment . 59
13.12 Flow Control Parameter Negotiation . 59
13.13 Throughput Class Negotiation .
60
13.14 Closed User Group related facilities . 61
13.15 Bilateral Closed User Group related facilities . 66
13.16 Fast Select . 67
13.17 Fast Select Acceptance . 67
13.18 Reverse Charging . 68
13.19 Reverse Charging Acceptance . 68
13.20 Local Charging Prevention . 68
13.21 Network User Identification (NUI) related facilities . 68
13.22 Charging Information . 69
13.23 RPOA related facilities . 69
13.24 Hunt Group . 70
13.25 Cali Redirection and Call Deflection related facilities . 71
13.26 Called Line Address Modified Notification . 72
13.27 Transit Delay Selection and Indication . 73
14 Procedures for optional CCXTT-specified DTE facilities . 73
14.1 Calling Address extension . 73
14.2 Called Address Extension . 73
143 Minimum Throughput Class Negotiation .
74
iii
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ISO/IEC 8208 : 1990 (E)
Foreword
IS0 (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) together form a system for worldwide standardization as a whole. 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 approval before their acceptance as International Standards. They an approved in accordance
with procedures requiring at least 75% approval by the national bodies voting.
Intemational Standard ISO/iEC 8208 was prepared by Technical Committee ISOWC JTC 1, Information
technology.
This second edition cancels and replaces the first edition (IS0 8208:1987).
Amex A forms an integral part of ISO/IEC 8208. Annex B is for information only.
V
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INTERNATIONAL STANDARD ISOAEC 8208 : 1990 (E)
Information technology ~ - I---_ Data communications -
Protocol) for Data Terminal Equipment
~ "---
i
1 scope 2 Normative references
The following standards and recommendations contain
This International Standard specifies the procedures, formats
and facilities at the Packet Layer for Data Terminal Equipment provisions which, through reference in this text, constitute
(DTE) operating in conformarice with CClTï Recommendation of
provisions of this Intemational Standard. At the time
X.25. Both Virtual Call and Permanent Virtual Circuit modes publication, the editions indicated were valid. All standards
ration are covered. and recommendations are subject to revision, and parties to
i ~~ *A" " - II.
agreements based on this International Standard are encouraged
_erein\can be used in both
to investigate the possibility of applying the most recent
(OSI) and non-OS1
editions of the standards and recommendations listed below.
environments. When used within the context of OSI, the
Members of IEC and IS0 maintain registers of currently valid
Packet Layer protocol is encompassed in the Network Layer of
International Standards. The CClTï secretariat maintains a
the OS1 Reference Model, IS0 7498.
register of currently valid CClTï Recommendations.
This International Standard covers DTE operation at the Packet
Layer when accessing a public or private packet-switched IS0 7498 : 1984, I@ormation processing systems - Open
network conforming to CCITT Recommendation X.25 by Systems Interconnection - Basic Reference Model (see also
means of a dedicated path or a circuit-switched connection. It
CCm Recommendation X.200, CCITï Blue Book, 1988).
also covers the additional Packet Layer procedures necessary
for two DTEs conforming to this International Standard to IS0 7776 : 1986, Information processing systems - Data
communicate directly (i.e., without an intervening packet- communications - High-level data link control procedures -
switched network) over a dedicated path, a circuit-switched
Description of the X.25 LAPB-compatible DTE data link
connection, or a local area network (LAN). procedures.
This International Standard also covers private networks that IS0 8348 : 1987, Information processing systems - Data
use CCITT Recommendation X.25 to connect to packet- communications - Network service definition (see also CCITl
switched public data networks and that may also offer an X.25 Recommendation X.213, CCITT Blue Book, 1988).
interface to a DTE (see annex A).
IS0 8348lAdd. 2 : 1988, Information processing systems -
The first edition of this International Standard was based on the
Data communications - Network service definition -
1984 CCITT Red Book text of Recommendation X.25. It also
Addendum 2: Network layer addressing (see also CCITT
contained the necessary provisions for compatibility with the
Recommendation X.213, CCUT Blue Book, 1988).
earlier 1980 CClTï Yellow Book text of Recommendation
X.25. This second edition is based on the 1488 CCl'lT Blue
IS0 8348lAdd. 3 : 1988, Information processing systerny -
Book text of Recommendation X.25. Retained within this
Data communications - Network service definition -
second edition are the necessary provisions for compatibility
Addendum 3: Additional features of the network service (see
with the 1984 and 1980 versions of X.25. The differences
also CCITï Recommendation X.213, CCITï Blue Book, 1988)
between the first and second editions of this International
Standard are summarized in annex B. IS0 8878 : 1987, Information processing systems - Daid
communications - Use of X.2.5 to provide the OS1 connection-
It should be noted that this International Standard and CClTï
mode network service (see also CC'ITT Recommendation X.223,
Recommendation X.25 as it applies to DTEs are different in
CCITï Blue Book, 1988).
scope. This International Standard contains the specifications
that Recommendation X.25 places on DTEs. In addition, this IS0 8880-2 : 1990, Information technology - Dacl
International Standard contains added specifications to facilitate
communications - Protocol combinations to provide ami
interworking between DTEs and to cover direct DTE-to-DTE
support the OS1 network service - Part 2: Provision and
operation. This broader scope has to be recognized in the support of the connection-mode network service.
application of this International Standard.
ISO/IEC 8881 : 1989, Information processing systems - Duta
communications - Use of the X.25 packet level protocol in
local area networks.
1
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ISO/IEC 8208 : 1990 (E)
Link Layer protocol for transmission to a DXE. On the
ISO/iEC 8886 : 1990, Information technology - Data
receiving side, the Packet Layer in a DTE performs the basic
communications - Data link service definition for Open
functions of receiving packets from the Data Link Layer,
Systems Interconnection (see also CCIlT Recommendation
checking packets for correctness, stripping off packet headers,
X.212, CCIIT Blue Book, 1988).
and formulating messages from the packetized user data and
ISO/reC 9574 : 1989, Information technology -
passing them to a higher layer entity in the DTE.
Telecommunications and information exchange between systems
This International Standard presents a description of the Packet
- Provision of the OSI connection-male network service by
Layer for "Virtual Call" service and "Permanent Virtual
packet mode terminal equipment connected to an Integrated
Service Digital Network (ISDN). Circuit" service.
The following information is presented
ISO/iEC TR 10029 : 1989. Information technology -
Telecommunications and information exchange between systems
3);
general considerations (clause
- Operation of an X.25 intenvorking unit.
procedures for exchanging packets across a DTEDXE
interface (clauses 4 through 11). Clause 5 applies to
CCTï Recommendation D.12, Measurement unit for charging
the setup and clearing procedures for Virtual Call
by volume in the international packet-switched data
service, while the other clauses apply to both Virtual
transmission service, CCLT Blue Book, 1988.
Call service and Permanent Virtual Circuit service.;
CCïïï Recommendation X.2, International data transmission
packet formats (clause 12);
services and optional user facilities in public &ta network and
ISDNs, CClïT Blue Book, 1988.
procedures for optional user facilities that may be
CCïïï Recommendation X.25, Interface between data terminal available on a DTEDXE interface (clauses 13 and 14);
equipment (DTE) and data circuit-terminating equipment
formats for optional user facilities and registration-
(DCE) for terminals operating in the packet mode and
facilities (clauses 15 and 16, respectively);
connected to public data networks by dedicated circuit, CCIlT
coding of the Diagnostic Code Field (clause 17);
Blue Book, 1988.
timers and retransmission counts (clause 18);
CCïïï Recommendation X.29, Procedures for the exchange of
control information and user data between a packet
state diagrams and state tables (clauses 19 and 20,
assemblyldisassembly (PAD) facility and a packet mode DTE or
respectively); and
another PAD, CCIIT Blue Book, 1988.
applications of this International Standard to private
CCïïï Recommendation X.31, Support of packet mode
networks that connect to a packet-switched public data
terminal equipment by an ISDN, CCIlT Blue Book, 1988.
network and that may also offer an X.25 interface to a
CCïïï Recommendation X.32, Interface between data terminal DTE (see annex A).
equipment (DTE) and data circuit-terminating equipment
To facilitate comprehension of this International Standard, a
(DCE) for terminals operating in the packet mode and
number of conventions have been adopted in the presentation of
accessing a packet switched public data network through a
the text:
public switched telephone network or an integrated services
digital network or a circuit switched public data network, the names of states and packets are in full capitals;
a)
CClïT Blue Book, 1988.
the names of the optional user facilities, packet fields,
b)
CCïïï Recommendation X.96, Call progress signals in public causes and diagnostics are in initial capitals;
data networkr, CCIIT Blue Book, 1988.
italicized tat is used to denote differences between
c)
CCI" Recommendation X.244. Procedure for the exchange of Virtual Call and Permanent Virtual Circuit service and
protocol identification during virtual call establishment on between DTEDTE and DTE/DCE interfaces (entire
packet-switched public data networks, CCITT Blue Book, 1988. clauses or subclauses that pertain to one service or to
one interface type are not italicized; the appropriate
3 General considerations environment is denoted at the beginning of the clause
or subclause);
This International Standard defines, from the viewpoint of a
DTE, the Packet Layer, which governs the transfer of packets terms not explicitly defined within this International
at a DTEDCE or DTE/DTE interface.') On the transmitting Standard are taken from the referenced CClTï X-series
side, the Packet Layer in a sending DTE performs the basic recommendations.
function of packetizing messages delivered by a higher layer
The Packet Layer procedures in this International Standard are
entity in the same DTE before giving the information to a Data
based on an underlying service (for example, that provided by
1) The term "DXE" is used in those contcxta whm it wmid not maner whether a DTE or a DCE was being rcfd to. Therefore, this International Standard can hL
viewed as defining the Packs hycr at the iYïEDXE inmfaffi.
2
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ISO/IEC 8208 : 1990 (E)
expanded capabilities for the following optional user
IS0 7776 or, more generally, the provision of the OS1 Data
a)
Link Service defined in ISO/IEC 8886) that provides: facilities
a) a negligible residual-bit-error rate; - Network User Identification (NUI) related facilities
(see 13.21),
b) a negligible out-of-sequence rate; and
- RPOA related facilities (see 13.23), and
c) a negligible packet-loss and duplication rate.
- Call Redirection and Call Deflection related
The Packet Layer provides the following functional capabilities
facilities (see 13.25);
that facilitate reliable and efficient data communications:
for 1984 operation, Call Deflection and NUI Override
a) multiplexing - the ability to support multiple
were not àefined and the NUI and RPOA facilities
communications;
were not explicitly separated into subscription and
negotiation facilities;
b) data transfer - the ability to send and receive data;
the following CCITT-specifred DTE facilities
c) flow control - the ability to control the flow of data;
b)
- Priority (see 14.5). and
d) interrupt transfer - the ability to send and receive a
small amount of information independent of the data
- Protection (see 14.6);
stream;
for 1984 operation the above facilities were not
error control - the ability to detect Packet Layer
e)
defined;
errors;
coding of the following CCR"T-.vpecifred DTE facilities
e)
f) reset and restart - the ability to reinitialize
were modifred
communication paths in the event that Packet Layer
errors are encountered. - Called Address Extension (see 15.3.2.1), ami
A number of design principles were used in the formulation of - Calling Address Extension (see 15.3.2.2);
the Packet Layer procedures for DTEs specified in this
for 1984 operation only BCD encoding of the
Intemational Standard
addresses is permitted.
a) conform fully to CCITT Recommendation X.25 for
the throughput class of 64 O00 bids; for 1984 operation
d)
operation with a packet-switched network;
the largest throughput class is 48 O00 bids.
b) minimize the differences between operating with a
3.1.2 Limitations for compatibility with X.25-1980
packet-switched network and operating directly with
another DTE; For DTEs needing to operate with the 1980 (Yellow Book)
version of Recommendation X.25, the following 1984
c) provide, where possible, the opportunity for recovery
capabilities are not used in addition to those cited in 3.1.1:
from an error condition without incurring data loss at
the Packet Layer; maximum User Data Field lengths in DATA packets of
a)
2 048 and 4 096 octets (see 6.2); for 1980 operation,
align the services provided by the Packet Layer with
d)
the largest maximum User Data Field length allowed is
the Network Layer services defined for ûpen Systems
1 024 octets;
Interconnection; and
b) Facility Fields in CU REQUmT, INCOMING
e) follow the organization of text in CCI7T
CALL, CALL ACCEPTED, and CALL CONNECTED
Recommendation X.25.
packets with a length from 64 to 109 octets (see
3.1 Compatibility with versions of CCITT 12.2.1.1 and 12.2.2.1); for 1980 operation, this field is
limited to 63 octets and bit 7 of the Facility Length
Recommendation X.25
Field shall be set to 0;
The Packet Layer procedures and formats specified in this
International Standard are compatible with the 1988 (Blue c) cause codes with bit 8 set to ono in CLEAR
Book) version of CCIlT Recommendation X.25. REQUESTIINDICATION. RESET
REQUESTANDIC ATION, and RESTART
NOTE - The TOANPI capability introduced into the 1988 version of
REQUEST/INDICATION packets (see 12.2.3.1.1,
CCITï Recommendation X.25 is not included in this Intemationai
12.5.1.1, and 12.6.1.1, respectively); for 1980
Standard since CCITï has designated it for further study.
operation, this bit shall be set to zero;
For DTEs needing to operate with the earlicr versions of
d) rwnzero Address Length and Facilio Length Fields in
Recommendation X.25, the following restrictions apply.
CLEAR REQUEST and CLEAR INDiCA'I'ION packets
3.1.1 Limitations for compatibility with X.25-1984
(see 12.23.2); for 1980 operation, these length frelds
shall indicate zero octets and may only be present
For DTEs needing to operate with the 1984 (Red Book) version
when the packet contains a Clear User Data Field;
of Recommendation X.25, the following 1988 capabilities are
not used:
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ISO/IEC 8208 : 1990 (E)
the extended format for CLEAR CONFIRMATION
i) the CCm-specified DTE facilities and the associated
packets (see 122.4.2); for 1980 operation. only the facility marker (see clause 14 and 15.1, respectively);
basic format may be used; for 1980 operation, these facilities and the marker
cannot be used.
Interrupt User Data Fields in INTERRUPT packets
containing from two to 32 octets (see 12.3.2); for 1980 3.2 Environments
operation, this field shall contain exactly one octet;
The DTE aspects of the Packet Layer protocol set forth in this
the following optional user facilities: International Standard are applicable to a number of
environments including:
- On-line Facility Registration (see 13.1),
a) DTE/DCE operation:
- Local Charging Prevention (see 13.20).
- DTE access to a DCE via a dedicated path,
- Network User Identification (see 13.21),
- DTE access to a DCE via a circuit-switched
- Charging IMormation (see 13.22),
connection (circuit-switched data network, circuit-
- Hunt Group (see 13.24), switched capability of an Integrated Services
Digital Network (ISDN), or the switched telephone
- Call Redirection and Call Dejection Notification
network). Additional considerations are given in
(see 1325),
3.4.
- Called Line Address Modified Notification (see
13.26), and NOTES
1 The situation where the "DW is a private network
- Transit Delay Selection and Indication (see 13.27);
accessing a public network DCE is covered in annex A.
for 1980 operation, the above facilities cannot be used,
2 The DCE may be a packet-switched data network operating
expanded capabilities for the following optional user
in accordance with CClTï Recommendatio
...
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