ISO/IEC 8073:1988
(Main)Information processing systems — Open Systems Interconnection — Connection oriented transport protocol specification
Information processing systems — Open Systems Interconnection — Connection oriented transport protocol specification
Systèmes de traitement de l'information — Interconnexion de systèmes ouverts — Protocole de transport en mode connexion
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Standards Content (Sample)
INTER NATIONAL
STANDARD WWN U
Second edition
1988- 12-1 5
Information processing systems - Open
Systems Interconnection - Connection
oriented transport protocol specification
Systèmes de traitement de l'information - Interconnexion de systèmes
ouverts - Protocole de transport en mode connexion
Reference number
ISO/IEC 8073: 1988 (E)
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ISO/IEC 8073 : 1988 (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 develop-
ment 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 accep-
tance as International Standards. They are approved in accordance with procedures re-
quiring at least 75 % approval by the national bodies voting.
International Standard ISW/IEC 8073 was prepared by Joint Technical Committee
ISO/IEC JTC 1, information technology.
This second edition cancels and replaces the first edition (IS0 8073 : 1986) and includes
technical revisions to the following: subclause 4.4; table 2; subclauses 6.5, 6.7, 6.9,
6.12 and 6.13; table 5; subclauses 6.14, 6.17 and 12.2; figure 4; table 7; subclauses
13.2, 13.9 and 14.6; tables 15, 17, 18 and 19; clause A.6; and tables 22 and 23.
Users should note that all International Standards undergo revision from time to time
and that any reference made herein to any other International Standard implies its
latest edition, unless otherwise stated.
Annex A forms an integral part of this International Standard. Annex B is for informa-
tion only.
O ISO/IEC 1988
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any
means, electronic or mechanical, including photocopying and microfilm, without permission in
writing from the publisher.
ISO/IEC Copyright Office, P.O. Box 56, 1211 Geneva 20, Switzerland
Printed in Switzerland
ii
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ISO/IEC 8073 : 1988 (E)
Contents
Page
O Introduction . 1
1 Scope and field of application . 2
2 References . 2
Section one : General
3 Definitions . 3
4 Symbols and abbreviations . 4
5 Overview of the Transport Protocol . 4
Section two : Transport protocol specification
6 Elements of procedure . 9
7 Protocolclasses . 22
8 Specification for class O : Simple class . 23
9 Specification for class 1 : Basic error recovery class . 23
10 Specification for class2 : Multiplexing class . 24
Specification for class 3 : Error recovery and multiplexing class . 26
11
12 Specification for class 4 : Error detection and recovery class . 27
13 Structure and encoding of TPDUs . 35
Section three : Conformance
14 Conformance . 50
Annexes
A Statetables . 51
B Checksum algorithms . 66
iii
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a
O
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INTERNATIONAL STANDARD ISO/IEC 8073 : 1988 (E)
Information processing systems - Open
Systems Interconnection - Connection
oriented transport protocol specification
O Introduction a) different throughput;
This International Standard is one of a set of International Stan-
b) different error rates;
dards produced to facilitate the interconnection of information
processing systems. This set of International Standards covers
c) integrity of data requirements;
the services and protocols required to achieve such inter-
d) reliability requirements.
a connection.
The Transport Protocol Standard is positioned with respect to
It does not require an implementation to use all of these
other related International Standards by the layers defined in
mechanisms, nor does it define methods for measuring achiev-
the Reference Model for Open Systems Interconnection
ed quality of service or criteria for deciding when to release
(IS0 7498). It is most closely related to, and lies within the field
transport connections following quality of service degradation.
of application of the Transport Service Standard (IS0 8072). It
also uses and makes reference to the Network Service Stan-
The primary aim of this International Standard is to provide a
dard (IS0 8348), whose provisions it assumes in order to
set of rules for communication expressed in terms of the pro-
accomplish the transport protocol’s aims. The interrelationship
cedures to be carried out by peer entities at the time of com-
of these International Standards is illustrated in figure 1.
munication. These rules for communication are intended to
provide a sound basis for development in order to serve a var-
This International Standard specifies a common encoding and
iety of purposes i.e. :
a number of classes of transport protocol procedures to be
used with different network qualities of service.
a) as a guide for implementors and designers;
It is intended that the Transport Protocol should be simple but
b) for use in the testing and procurement of equipment;
general enough to cater for the total range of Network Service
qualities possible, without restricting future extensions.
c) as part of an agreement for the admittance of systems
The protocol is structured to give rise to classes of protocol into the open systems environment;
which are designed to minimize possible incompatibilities and
implementation costs.
d) as a refinement of the understanding of OSI.
The classes are selectable with respect to the Transport and As it is expected that the initial users of this International Stan-
Network Services in providing the required quality of service for dard will be designers and implementors of equipment this
the interconnection of two session entities (each class provides International Standard contains, in notes or in annexes,
a different set of functions for enhancement of service guidance on the implementation of the procedures defined
qualities). herein.
This International Standard defines mechanisms that can be It should be noted that, as the number of valid protocol
used to optimize network tariffs and enhance the following sequences is very large, it is not possible with current
qualities of service :
technology to verify that an implementation will operate the
I
TRANSPORT SERVICE DEFINITION
A
Transport Reference to aims - - - - - - - - J
Protocol
Reference to assumptions - - - ,
t
NETWORK SERVICE DEFINITION
Figure 1 - Relationship between the Transport Protocol and adjacent services
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ISO/IEC 8073 : 1988 (E)
protocol defined in this International Standard correctly under b) the means of negotiating the class of procedures to be
all circumstances. It is possible by means of testing to establish used by the transport entities;
confidence that an implementation correctly operates the pro-
tocol in a representative sample of circumstances. It is,
c) the structure and encoding of the transport protocol
however, intended that this International Standard can be used
data units used for the transfer of data and control infor-
in circumstances where two implementations fail to com-
mation.
municate in order to determine whether one or both have failed
to operate the protocol correctly. The procedures are defined in terms of
This International Standard contains a section on conformance the interactions between peer transport entities through
a)
of equipment claiming to implement the procedures in this
the exchange of transport protocol data units;
International Standard. Attention is drawn to the fact that this
International Standard does not contain any tests to
b) the interactions between a transport entity and the
demonstrate this conformance. transport service user in the same system through the
exchange of transport service primitives;
The variations and options available within this International
Standard are essential as they enable a transport service to be c) the interactions between a transport entity and the net-
provided for a wide variety of applications over a variety of net-
work service provider through the exchange of network ser-
work qualities. Thus, a minimally conforming implementation vice primitives.
will not be suitable for use in all possible circumstances. It is im-
portant, therefore, to qualify all references to this International These procedures are defined in the main text of this Inter-
Standard with statements of the options provided or required
national Standard supplemented by state tables in annex A.
or with statements of the intended purpose of provision or use.
These procedures are applicable to instances of communication
between systems which support the Transport Layer of the OS1
1 Scope and field of application
Reference Model and which wish to interconnect in an open
systems environment.
This International Standard specifies
This International Standard specifies, in clause 14, confor-
a) five classes of procedures :
mance requirements for systems implementing these pro-
cedures. It does not contain tests which can be used to
1) class O : simple class; demonstrate this conformance.
2) class 1 : basic error recovery class;
2 References
3) class 2 : multiplexing class;
IS0 7498, Information processing systems - Open Systems
4) class 3 : error recovery and multiplexing class;
Interconnection - Basic Reference Model.
5) class 4 : error detection and recovery class;
IS0 8072, Information processing systems - Open Systems
Interconnection - Transport service definition.
for the connection oriented transfer of data and control
information from one transport entity to a peer transport
IS0 8348, Information processing systems - Data com-
entity;
munications - Network service definition.
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SO/IEC 8073 : 1988 (E)
Section one : General
3 Definitions 3.2.10 alternative class : A protocol class that the initiator
indicates in a CR TPDU as an alternative choice for use over the
NOTE - The definitions contained in this clause make use of abbrevi- transport connection.
ations defined in clause 4.
3.2.11 proposed class : A preferred class or an alternative
3.1 This International Standard is based on the concepts
class.
developed in IS0 7498 and makes use of the following terms
defined in it :
3.2.12 selected class : The protocol class that the responder
indicates in a CC TPDU that it has chosen for use over the
ai concatenation and separation;
transport connection.
b) segmenting and reassembling;
3.2.13 proposed parameter : The value for a parameter that
the initiator indicates in a CR TPDU that it wishes to use over
c) multiplexing and demultiplexing;
the transport connection.
0 di splitting and recombining;
3.2.14 selected parameter : The value for a parameter that
e) flow control.
the responder indicates in a CC TPDU that it has chosen for use
over the transport connection.
3.2 For the purposes of this International Standard, the
following definitions apply :
3.2.15 error indication : An N-RESET indication, or an
N-DISCONNECT indication with a reason code indicating an
error, that a transport entity receives from the NS-provider.
3.2.1 equipment : Hardware or software or a combination of
both; it need not be physically distinct within a computer
system.
3.2.16 invalid TPDU : A TPDU that does not comply with
the requirements of this International Standard for structure
3.2.2 transport service user : An abstract representation of and encoding.
the totality of those entities within a single system that make
use of the transport service.
3.2.17 protocol error : A TPDU whose use does not comply
with the procedures for the class.
3.2.3 network service provider : An abstract machine that
models the totality of the entities providing the network
3.2.18 sequence number :
service, as viewed by a transport entity.
a) the number in the TPDU-NR field of a DT TPDU that in-
dicates the order in which the DT TPDU was transmitted by
3.2.4 local matter : A decision made by a system concerning
its behaviour in the Transport Layer that is not subject to the a transport entity;
requirements of this protocol.
b) the number in the YR-TU-NR field of an AK or RJ
TPDU that indicates the sequence number of the next DT
3.2.5 initiator : A transport entity that initiates a CR TPDU.
TPDU expected to be received by a transport entity.
3.2.6 responder : A transport entity with whom an initiator
3.2.19 transmit window : The set of consecutive sequence
wishes to establish a transport connection.
numbers which a transport entity has been authorised by its
at a given time on a given transport connec-
peer entity to send
NOTE - Initiator and responder are defined with respect to a single
tion.
transport connection. A transport entity can be both an initiator and
responder simultaneously.
3.2.20 lower window edge : The lowest sequence number
in a transmit window.
3.2.7 sending transport entity : A transport entity that
sends a given TPDU.
3.2.21 upper window edge : The sequence number which
3.2.8 receiving transport entity : A transport entity that is one greater than the highest sequence number in the
transmit window.
receives a given TPDU.
3.2.9 preferred class : The protocol class that the initiator
3.2.22 upper window edge allocated to the peer entity :
indicates in a CR TPDU as its first choice for use over the
The value that a transport entity communicates to its peer enti-
transport connection. ty to be interpreted as its new upper window edge.
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ISO/IEC 8073 : 1988 (E)
3.2.23 closed window : A transmit window that contains no 4.4 Times and associated variables
sequence number.
T1 Local retransmission time
N The maximum number of transmissions
3.2.24 window information : Information contained in a
L Time bound on reference and sequence number
TPDU relating to the upper and the lower window edges.
I Inactivity time
W Window time
3.2.25 frozen reference : A reference that is not available
reassignment/resynchronization
TTR Time to try
for assignment to a connection because of the requirements
TWR Time to wait for reassignment/resynchronization
of 6.18.
TS 1 Supervisory timer 1
TS2 Supervisory timer 2
NSDU lifetime local-to-remote
3.2.26 unassigned reference : A reference that is neither
MLR
NSDU lifetime remote-to-local
currently in use for identifying a transport connection nor MRL
Expected maximum transit delay local-to-remote
which is in a frozen state.
ELR
Expected maximum transit delay remote-to-local
ERL
R Persistence time
3.2.n transparent (data) : TS-user data that is transferred
AL Local acknowledgement time
intact between transport entities and which is unavailable for
AR Remote acknowledgement time
use by the transport entities.
4.5 Miscellaneous
3.2.28 owner (of a network connection) : The transport
entity that issued the N-CONNECT request leading to the cre-
TS-user Transport-service user
ation of that network connection.
TSAP Transport-service-access-point
NS-provider Network service provider
3.2.29 retained TPDU : A TPDU that is subject to the
AP Network-service-access-point
retransmission procedure or retention until acknowledgement 00s Quality of service
procedure and is available for possible retransmission.
5 Overview of the Transport Protocol
4 Symbols and abbreviations
NOTE - This overview is not exhaustive and has been provided for
guidance.
4.1 Data units
TPDU Transport-protocol-data-unit
5.1 Service provided by the Transport Layer
TSDU Transport-service-data-unit
NSDU Network-service-data-unit
The protocol specified in this International Standard supports
the Transport Service defined in IS0 8072.
4.2 Types of Transport Protocol data units
Information is transferred to and from the TS-user in the
transport service primitives listed in table 1.
CR TPDU Connection request TPDU
CC TPDU Connection confirm TPDU
0
Disconnect request TPDU
DR TPDU
5.2 Service assumed from the Network Layer
DC TPDU Disconnect confirm TPDU
DT TPDU Data TPDU
The protocol specified in this International Standard assumes
ED TPDU Expedited data TPDU
the use of the Network Service defined in IS0 8348.
AK TPDU Data acknowledge TPDU
EA TPDU
Expedited acknowledge TPDU Information is transferred to and from the NS-provider in the
RJ TPDU Reject TPDU
network service primitives listed in table 2.
ER TPDU Error TPDU
NOTES
4-3 TPDU fields
1 The parameters listed in table 2 are those in the current network
service (see IS0 8348).
LI Length indicator (field)
2 The way the parameters are exchanged between the transport en-
CDT Credit (field)
tity and the NS-provider is a local matter.
TSAP-ID Transport-service-access-point identifier
(field)
5.3 Functions of the Transport Layer
DST-REF Destination reference (field)
SRC-REF Source reference (field)
EOT End of TSDU mark
5.3.1 Overview of functions
TPDU-NR DT TPDU number (field)
ED-TPDU-NR ED TPDU number (field)
The functions in the Transport Layer are those necessary to
YR-TU-NR Sequence number response (field)
bridge the gap between the services available from the Network
YR-EDTU-NR ED TPDU number response (field)
Layer and those to be offered to the TS-users.
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ISO/IEC 8073 : 1988 (E)
Table 1 - Transport service primitives
Parameters
Primitives
Called Address
T-CONNECT request
Calling Address
indication
Expedited data option
Quality of service
TS-user-data
T-CONNECT response Responding address
Quality of service
confirm Expedited data option
TS-user-data
T-DATA request TS-user-data
indication
T-EXPEDITED DATA request TS-user-data
indication
T-DISCONNECT request TS-user-data
T-DISCONNECT indication Disconnect reason
TS-user-data
Table 2 - Network service primitives
Parameters XIYIZ
XIY
Primitives
~~ ~
Called Address X
request X
N-CONNECT
Calling Address X
Receipt confirmation selection Y
indication X
Expedited data selection Y
QOS parameter set X
N S-user-data Z
X
N-CONNECT response Responding Address
Receipt confirmation selection
confirmation X
Expedited data selection
QOS parameter set
N-user-data
N-user-data X
N-DATA request X
Confirmation request Y
indication X
a
N-DATA ACKNOWLEDGE request
indication
NS-user-data Y
N-EXPEDITED DATA request
indication
Z
Reason
request
z
Originator
indication
Z
Reason
N-RESET response
confirm
X Reason
N-DISCONNECT request
NS-user-data
Responding address
Originator
indication X
Reason
NS-user-data
Responding address
Key :
X : The Transport Protocol assumes that this facility is provided in all networks.
Y : The Transport Protocol assumes that this facility is provided in some networks and a mechanism is provided to optionally use the facility.
Z : The Transport Protocol does not use this parameter and will ignore it when received in the network service primitive.
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ISO/IEC 8073 : 1988 (E)
provide a means to distinguish between two different
f)
The functions in the Transport Layer are concerned with the
transport connections (see 6.5);
enhancement of quality of service, including aspects of cost
optimization.
g) transport of TS-user data (see 6.5).
These functions are grouped below into those used at all times
during a transport connection and those concerned with con- 5.3.1.3 Data transfer
nection establishment, data transfer and release.
The purpose of data transfer is to permit duplex transmission of
NOTE - This International Standard does not include the following
TSDUs between the two TS-users connected by the transport
functions which are under consideration for inclusion in future editions
is achieved by means of two-way
connection. This purpose
of this International Standard :
simultaneous communication and by the following functions,
some of which are used or not used in accordance with the
a) encryption;
result of the selection performed in connection establishment :
b) accounting mechanisms;
ci status exchanges and monitoring of QOS;
a) concatenation and separation (see 6.4) : a function
used to collect several TPDUs into a single NSDU at the
di blocking:
sending transport entity and to separate the TPDUs at the
e) temporary release of network connections;
receiving transport entity;
fi alternative checksum algorithm.
b) segmenting and reassembling (see 6.3) : a function
at
used to segment a single data TSDU into multiple TPDUs
5.3.1.1 Functions used at all times
the sending transport entity and to reassemble them into
their original format at the receiving transport entity;
The following functions, depending upon the selected class
and options, are used at all times during a transport connec-
c) splitting and recombining (see 6.23) : a function allow-
tion :
ing the simultaneous use of two or more network connec-
tions to support the same transport connection;
transmission of TPDUs (see 6.2 and 6.9);
a)
d) flow control (see 6.16) : a function used to regulate the
flow of TPDUs between two transport entities on one
b) multiplexing and demultiplexing (see 6.15) : a function
transport connection;
used to share a single network connection between two or
more transport connections;
e) transport connection identification : a means to unique-
ly identify a transport connection between the pair of
c) error detection (see 6.10, 6.13 and 6.17) : a function
transport entities supporting the connection during the
used to detect the loss, corruption, duplication, misordering
lifetime of the transport connection;
or misdelivery of TPDUs;
f) expedited data (see 6.11) : a function used to bypass
d) errorrecovery(see6.12, 6.14, 6.18,6.19, 6.20,6.21 and
the flow control of normal data TPDU. Expedited data
6.22) : a function used to recover from detected and sig-
TPDU flow is controlled by separate flow control;
nalled errors.
g) TSDU delimiting (see 6.3) : a function used to deter-
mine the beginning and ending of a TSDU.
5.3.1.2 Connection Establishment
The purpose of connection establishment is to establish a
5.3.1.4 Release
transport connection between two TS-users. The following
functions of the transport layer during this phase match the TS-
The purpose of release (see 6.7 and 6.8) is to provide discon-
users’ requested quality of service with the services offered by nection of the transport connection, regardless of the current
the network layer : activity.
a) select the network service which best matches the
5.4 Classes and options
requirement of the TS-user taking into account charges for
various services (see 6.5);
5.4.1 General
decide whether to multiplex multiple transport connec-
b)
The functions of the Transport Layer have been organized into
tions onto a single network connection (see 6.5);
classes and options.
establish the optimum TPDU size (see 6.5);
c)
A class defines a set of functions. Options define those func-
tions within a class which may or may not be used.
d) select the functions that will be operational upon enter-
ing the data transfer phase (see 6.5);
This International Standard defines five classes of protocol :
a) class O : simple class;
e) map transport addresses onto network addresses;
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ISO/IEC 8073 : 1988 (E)
The main purpose of the class is to recover from network
class 1 : basic error recovery class;
b)
disconnect or reset.
c) class 2 : multiplexing class;
Selection of this class is usually based on reliability criteria.
Class 1 has been designed to be used with type B network con-
class 3 : error recovery and multiplexing class;
d)
nections.
e) class 4 : error detection and recovery class.
5.4.6 Characteristics of class 2
NOTES
1 Transport connections of classes 2,3 and 4 may be multiplexed
5.4.6.1 General
together onto the same network connection.
2 Classes O to 3 do not specify mechanisms to detect unsignalled net-
Class 2 provides a way to multiplex several transport connec-
work transmission failures.
tions onto a single network connection. This class has been
designed to be used with type A network connections.
5.4.2 Negotiation
5.4.6.2 Use of explicit flow control
The use of classes and options is negotiated during connection
establishment. The choice made by the transport entities will
The objective is to provide flow control to help avoid conges-
tion at transport-connection-end-points and on the network
a depend
-
connection. Typical use is when traffic is heavy and con-
a) the TS-users’ requirements expressed via T-CONNECT
tinuous, or when there is intensive multiplexing. Use of flow
service primitives;
control can optimize response times and resource utilization.
b) the quality of the available network services:
Non-use of explicit flow control
5.4.6.3
c) the user required service versus cost ratio acceptable to
the TS-user.
The objective is to provide a basic transport connection with
minimal overheads suitable when explicit disconnection of the
5.4.3 Choice of network connection
transport connection is desirable. The option would typically be
used for unsophisticated terminals, and when no multiplexing
The following list classifies network services in terms of quality
onto network connections is required. Expedited data is never
with respect to error behaviour in relation to user requirements; available.
its main purpose is to provide a basis for the decision regarding
which class of transport protocol should be used in conjunction
5.4.7 Characteristics of class 3
with given network connection :
Class 3 provides the characteristics of class 2 plus the ability to
ai Type A : Network connection with acceptable residual
recover from network disconnect or reset. Selection of this
error rate (for example not signalled by disconnect or reset)
class is usually based upon reliability criteria. Class 3 has been
and acceptable rate of signalled errors.
designed to be used with type B network connections.
b) Type B : Network connections with acceptable residual
error rate (for example not signalled by disconnect or reset)
5.4.8 Characteristics of class 4
but unacceptable rate of signalled errors.
Class 4 provides the characteristics of class 3, plus the capabil-
c) Type C : Network connections with unacceptable ity to detect and recover from errors which occur as a result of
residual error rate.
the low grade of service available from the NS-provider. The
kind of errors to be detected include : TPDU loss, TPDU
It is assumed that each transport entity is aware of the quality of sequence, TPDU duplication and TPDU corrup-
delivery out
of service provided by particular network connections. tion. These errors may affect control TPDUs as well as data
TPDUs.
5.4.4 Characteristics of class O
This class also provides for increased throughput capability and
additional resilience against network failure.
Class O provides the simplest type of transport connection and
is fully compatible with the CCITT Recommendation T.70 for
Class 4 has been designed to be used with type C network con-
teletex terminals.
nections.
Class O has been designed to be used with type A network con-
nections.
5.5 Model of the transport layer
5.4.5 Characteristics of class 1 A transport entity communicates with its TS-users through one
or more TSAPs by means of the service primitives as defined by
the transport service definition (see IS0 8072). Service
Class 1 provides a basic transport connection with minimal
overheads. primitives will cause or be the result of transport protocol data
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unit exchanges between the peer transport entities supporting Transport connection endpoints are identified in end systems
a transport connection. These protocol exchanges are effected so that
by an internal, implementation dependent, mechanism
using the services of the Network Layer as defined by the net- the TS-user and the transport entity can refer to each transport
work service definition (see IS0 8348) through one or more connection.
NSAPs.
TSAP
I I .
Transport entity Transport entity
-
-
NSAP NSAP
NOTE - For the purposes of illustration, figure 2 shows only one TSAP and one NSAP for each transport entity. In certain instances, more than one
TSAP and/or more than one NSAP may be associated with a particular transport entity.
...
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