ISO/IEC TR 10029:1989
(Main)Information technology — Telecommunications and information exchange between systems — Operation of an X.25 interworking unit
Information technology — Telecommunications and information exchange between systems — Operation of an X.25 interworking unit
Describes the function of the Interworking unit (IWU) in terms of the mapping between Protokol Data Units (PDUs) that it receives from one interface, and PDUs that it then transmits which could be on either interface of the IWU. Also describes procedures an IWU can initiate on each interface independently. Each interface corresponds to one instance of a DTE/DXE connection, and both interfaces of the Interworking Unit operate as a DTE as specified by ISO 8208. References: ISO 8208; 8880-2; 8881.
Systèmes de traitement de l'information — Communication de données — Fonctionnement d'une unité d'interfonctionnement X.25
General Information
Standards Content (Sample)
EOIIEC
TECHNICAL
TR 10029
REPORT
First edition
1989-03-15
Information technology - Telecommunications
and information exchange between systems -
Operation of an X.25 interworking unit
S yst&mes de traitement de l ’information - Communication de donndes -
Fonctionnement d ’une unit6 d7nterfonctionnement X.25
Reference number
ISO/IEC/TR 10029 : 1989 (E)
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ISO/IEC/TR 10029 : 1989 (E)
Contents Page
Foreword. iii
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Introduction iv
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1 Scope . .
2 Normative references 1
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3 Abbreviations 1
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4 General considerations 1
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5 Procedures for restart 2
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6 Procedures for virtual call setup and clearing . 2
7 Procedures for data and interrupt transfer . 3
8 Procedures for flow control 3
...........................
9 Procedures for reset . 3
10 Optional user facilities . 3
0 ISO/IEC 1989
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Printed in Switzerland.
ii
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ISO/IEC/TR 10029 : 1989 (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, ISOAEC JTC 1.
The main task of a technical committee is to prepare International Standards but in
exceptional circumstances, the publication of a technical report of one of the
following types may be proposed:
- type 1, when the necessary support within the technical committee cannot
be obtained for the publication of an International Standard, despite repeated
efforts;
- type 2, when the subject is still under technical development requiring
wider exposure;
- type 3, when a technical committee has collected data of a different kind
from that which is normally published as an International Standard ( ‘state of
the art ’, for example).
Technical reports of types 1 and 2 are subject to review within three years of
publication, to decide whether they can be transformed into International Standards.
Technical reports of type 3 do not necessarily have to be reviewed until the data they
provide are considered to be no longer valid or useful.
ISO/IEC/TR 10029, which is a technical report of type 2, was prepared by
lSO/lEC JTC 1, Information technology.
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ISO/IEC/TR 10029: 1989 (E)
Introduction
The preparation of IS0 8881 included, as an annex, the operation of an interworking
unit that would enable a Local Area Network (LAN) to be interconnected to other X.25
Wide Area Networks (WANs). During these studies it became clear that the field of
application of the X.25 interworking unit was not limited to LAN/WAN interconnection
and the work was separated from IS0 8881 and attached to IS0 8880-2.
Following further development as part of IS0 8880-2 it was observed that the
technical content was in the form of guidance to implementors and as a consequence
the document contained no specification nor conformance requirements. However
those studies indicated that further consideration should be directed towards IS0
8208 and in particular to the classification of facilities. For example, a facility marked
as applicable only to DTE/DCE operation could also be applicable to DTE/DTE
operation where one of the DTE ’s is an X.25 interworking unit (IWU) as described in
this technical report.
Rather than delay the publication of this technical material until the complementary
studies have been concluded, this technical report is published in order to give
guidance to implementors on the operation of an IWU.
Various networks employ the IS0 8208 X.25 Packet Layer Protocol (PLP) to carry
communications between data terminals. An IWU provides the means to interconnect
those networks in order that a terminal on one network can communicate with a
terminal or make use of facilities on a different network. Typically, an IWU could be
located between a LAN where the attached terminals use the X.25 PLP as defined in
IS0 8881, and a WAN which is a Packet Switched Data Network where the terminals
use the X.25 PLP protocol as defined in IS0 8208, or between LANs.
This Technical Report describes the functions performed by an IWU which operates
between subnetworks that use IS0 8208 in conjunction with various lower layer
protocols. The IS0 8208 protocols on each side of the IWU are closely coupled but
are not necessarily equal in configuration. The protocols at the lower layers are
independent of each other.
NOTE - The method of interworking described in this Technical Report is a method of
internetworking at the level of the IS0 8208 Protocol Data Units. A standard specifying
internetworking using the semantics of the OSI Network Service is currently being developed.
In order to avoid duplicating the definitions for the operation of the X.25 PLP in this
Technical Report, extensive reference to specific text in IS0 8208 is made. The
references given are to clauses, figures, and tables as identified in the first edition of
IS0 8208.
iV
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ISO/IEC/TR 10029: 1989 (E)
TECHNICAL REPORT
Information technology - Telecommunications and
information exchange between systems - Operation of
an X.25 interworking unit
3 Abbreviations
1 Scope
DCE Data Circuit-terminating Equipment
This Technical Report describes the function of the IWU in
DTE Data Terminal Equipment
terms of the mapping between Protocol Data Units (PDUs)
IWU Interworking unit
that it receives from one interface, and PDUs that it then
LAN Local Area Network
transmits, which could be on either interface of the IWU.
OSI Open Systems Interconnection
Additionally, this Technical Report describes the
PDU Protocol Data Unit
procedures that an IWU can initiate on each interface
PLP Packet Level Protocol
independently.
WAN Wide Area Network
Each interface corresponds to one instance of a DTE/DXE
connection, and both interfaces of the Interworking Unit
4 General considerations
operate as a DTE as specified by IS0 8208.
NOTE - The term ‘DXE’ is used as defined in IS0 8208 meaning 4.1 Logical channels
“. .those contexts where it would not matter whether a DTE or a
DCE was being referred to.”
The logical channel identifiers used on one interface of the
IWU will not, in general, correspond to those used on the
other interface of the IWU. The IWU performs the mapping
2 Normative references
function between logical channel identifiers on the two
interfaces. This mapping is one-to-one and is established
The following standards contain provisions which, through
during Virtual Call setup.
reference in this text, constitute provisions of this
Technical Report. At the time of publication, the editions
4.2 Interface types and references
indicated were valid. All standards are subject to revision,
and parties to agreements based on this Technical Report
The operation of the IWU is described in terms of its two
are encouraged to investigate the possibility of applying the
interfaces. For ease of reference only, the two interfaces
most recent editions of the standards listed below.
are referred to as ‘interface 1’ and ‘interface 2 ’. Refer to
Members of IEC and IS0 maintain registers of currently
figure 1.
valid International Standards.
The procedures described in this Technical Report are
I SO 8208 : 1987, lnforma tion processing systems - Data
applicable to either interface. In this Technical Report
- X.25 Packet Level Protocol for Data
communications
external events, are described in terms of one direction
Terminal Equipment.
only; in some cases a corresponding event occurs on
interface 2. For events initiated by the IWU the procedures
- 11, Information processing systems - Pro-
IS0 8880-2: at both interfaces are described.
tocol combinations to provide and support the OS/ network
- Part 2: Provision and support of the connection-
service
mode network service.
4.3 Mapping between dissimilar protocol
configurations
- 11, Information processing systems - Data
IS0 8881:
communications - Use of the X.25 Packet Level Protocolin
Mapping between PDUs received on interface 1 might not be
Local Area Networks.
on a one-to-one basis to those transmitted on interface 2
due to the differences which are possible within IS0 8208.
1) To be published.
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ISO/IEC/TR 10029: 1989 (E)
PLP interface 1 IWU PLP interface 2
x.25 x.25 X.25
x.25
RELAY
PLP N PLP PLP y PLP
Each interface corresponds to one instance of a DTE/DX E connectio n. Both
8208.
interfaces operate as a DTE as specified by IS0
Figure 1 - Operation of an X.25 to X.25 IWU
interface 2 (available by default or through negotiation
5 Procedures for restart
if allowed on the interface);
5.1 Interface restart not initiated by the IWU
NOTE - If the IWU does not have segmentation and
reassembly capabilities, the IWU should ensure that the
When receiving a RESTART INDICATION packet on
maximum DATA packet size on each interface is identical. If
interface 1, the IWU confirms this restart by sending a
the packet sizes on interface 1 and interface 2 are
RESTAR
...
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