ISO/IEC 8073:1988

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

General Information

• Status: Withdrawn
• Publication Date: 28-Dec-1988
• Withdrawal Date: 28-Dec-1988
• ICS: 35.100.70 - Application layer
• Technical Committee: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
• Drafting Committee: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 17-Dec-1992
• Completion Date: 30-Oct-2025

Relations

• Amended By: ISO/IEC 8073:1988/Add 2:1989 - Information processing systems - Open Systems Interconnection - Connection oriented transport protocol specification - Addendum 2
• Effective Date: 06-Jun-2022
• Corrected By: ISO/IEC 8073:1988/Cor 3:1990 - Information processing systems - Open Systems Interconnection - Connection oriented transport protocol specification - Technical Corrigendum 3
• Effective Date: 06-Jun-2022
• Revised: ISO/IEC 8073:1992 - Information technology - Telecommunications and information exchange between systems - Open Systems Interconnection - Protocol for providing the connection-mode transport service
• Effective Date: 15-Apr-2008
• Revises: ISO 8073:1986 - Information processing systems - Open Systems Interconnection - Connection oriented transport protocol specification
• Effective Date: 15-Apr-2008
• Parent: ISO/IEC 8073:1988/Add 2:1989 - Information processing systems - Open Systems Interconnection - Connection oriented transport protocol specification - Addendum 2
• Effective Date: 18-Dec-2008
• Parent: ISO/IEC 8073:1988/Cor 3:1990 - Information processing systems - Open Systems Interconnection - Connection oriented transport protocol specification - Technical Corrigendum 3
• Effective Date: 15-Apr-2008

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)
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
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
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
a
O
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
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.
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.
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
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.
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.
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;
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
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.
Figure 2 - Model of the transport layer
ISO/IEC 8073 : 1988 (E)
Section two : Transport protocol specification
The non-owner (of the network connection) becomes aware of
6 Elements of procedure
the assignment when it receives
This clause contains elements of procedure which are used in
a) a CR TPDU during the connection establishment pro-
the specification of protocol classes in clauses 7 to 12. These
cedure (see 6.5); or
elements are not meaningful on their own.
b) an RJ TPDU or a retransmitted CR or DR TPDU during
The procedures define the transfer of TPDUs whose structure
the resynchronisation (see 6.14) and reassignment after
and coding is specified in clause 13. Transport entities shall
failure (see 6.12) procedures; or
accept and respond to any TPDU received in a valid NSDU and
may issue TPDUs initiating specific elements of procedure
c) any TPDU when splitting (see 6.23) is used.
specified in this clause.
NOTES
NOTE - Where network service primitives, TPDUs and parameters
used are not significant for a particular element of procedure, they
1 When a new network connection is created, the quality of service
in the specification.
have not been included
requested is a local matter, although it will normally be related to the
requirements of transport connection(s) expected to be assigned to it.
2 An existing network connection may also not be suitable if, for
6.1 Assignment to network connection
example, the quality of service requested for the transport connection
cannot be attained by using or enhancing the network connection.
6.1.1 Purpose
3 A network connection with no transport connection(s) assigned to
it, may be available after initial establishment, or because all of the
The procedure is used in all classes to assign transport connec- it have been released. It is
transRort connections previously assigned to
tions to network connections. recommended that only the owner of such a network connection
it. Furthermore, it is recommended that it not be releas-
should release
ed immediately after the transmission of the final TPDU of a transport
6.1.2 Network service primitives in response to CR TPDU or a DC TPDU
connection: either a DR TPDU
in response to DR TPDU. An appropriate delay will allow the TPDU
concerned to reach the other transport entity allowing the freeing of
The procedure uses the following network service primitives :
any resources associated with the transport connection concerned.
ai N-CONNECT; 4 After the failure of a network connection, transport connections
which were previously rnultiplexed together may be assigned to dif-
ferent network connections, and vice versa.
b) N-DISCONNECT.
6.1.3 Procedure 6.2 Transport protocol data unit (TPDU) transfer
Each transport connection shall be assigned to a network con-
6.2.1 Purpose
nection. The initiator may assign the transport connection to an
existing network connection of which it is the owner or to a
is used in all classes to convey
The TPDU transfer procedure
new network connection (see note 1) which it creates for this
transport protocol data units in user data fields of network ser-
purpose.
vice primitives.
The initiator shall not assign or reassign the transport connec-
6.2.2 Network service primitives
tion to an existing network connection if the protocol class(es1
proposed or the class in use for the transport connection are in-
The procedure uses the following network service primitives :
compatible with the current usage of the network connection
with respect to multiplexing (see note 21.
a) N-DATA;
During the resynchronization (see 6.14) and reassignment after
b) N-EXPEDITED DATA.
failure (see 6.12) procedures, a transport entity may reassign a
transport connection to another network connection joining
the same NSAPs, provided that it is the owner of the network
6.2.3 Procedure
connection and that the transport connection is assigned to
only one network connection at any given time.
The transport protocol data units (TPDUs) defined for the pro-
tocol are listed in 4.2.
During the splitting procedure (see 6-23], a transport entity may
assign a transport connection to any additional network con- When the network expedited variant has been selected for class
nection joining the same NSAPs, provided that it is the owner 1, the transport entities shall transmit and receive ED and EA
of the network connection and that multiplexing is possible on TPDUs as NS-user data parameters of N-EXPEDITED DATA
the network connection. primitives.
ISO/IEC 8073 : 1988 E)
A transport entity shall accept a valid set of concatenated
In all other cases, transport entities shall transmit and receive
TPDUs as NS-user data parameters of N-DATA primitives. TPDUs.
When a TPDU is put into an NS-user data parameter, the
NOTES
significance of the bits within an octet and the order of octets
1 The TPDUs within a concatenated set may be distinguished by
within a TPDU shall be as defined in 13.2.
means of the length indicator parameter.
2 The end of a TPDU containing data is indicated by the termination
NOTE - TPDUs may be concatenated (see 6.4).
of the NSDU.
The number of concatenated TPDUs referred to in 6.4.2.a) is
6.3 Segmenting and reassembling 3
bounded by the maximum number of transport connections which are
multiplexed together except during assignment or reassignment.
6.3.1 Purpose
The segmenting and reassembling procedure is used in all 6.5 Connection establishment
classes to map TSDUs onto TPDUs.
6.5.1 Purpose
6.3.2 TPDUs and parameter used
The procedure for connection establishment is used in all
The procedure makes use of the following TPDU and
classes to create a new transport connection.
parameter :
6.5.2 Network service primitives
DT TPDUs
- End of TSDU.
The procedure uses the following network service primitive :
N- DATA.
6.3.3 Procedure
A transport entity shall map a TSDU on to an ordered sequence
6.5.3 TPDUs and parameters used
of one or more DT TPDUs. This sequence shall not be inter-
rupted by other DT TPDUs on the same transport connection.
The procedure uses the following TPDUs and parameters :
All DT TPDUs except the last DT TPDU in a sequence greater
a) CRTPDU
than one shall have a length of data greater than zero.
- CDT;
NOTES
- DST-REF (set to zero);
1 The EOT parameter of a DT TPDU indicates whether or not there
- SRC-REF;
are subsequent DT TPDUs in the sequence.
- CLASS and OPTIONS (i.e. preferred class, use of
2 There is no requirement that the DT TPDUs shall be of the max-
extended format, non-use of explicit flow control in
imum length selected during connection establishment.
class 2);
- calling TSAP-ID;
6.4 Concatenation and separation
- called TSAP-ID;
6.4.1 Purpose
- TPDU size (proposed);
- version number;
The procedure for concatenation and separation is used in
- protection parameter;
classes 1, 2, 3 and 4 to convey multiple TPDUs in one NSDU.
- checksum;
6.4.2 Procedure
- additional option selection (i.e. use of network
expedited in class 1, use of receipt confirmation in
A transport entity may concatenate TPDUs from the same or
class 1, non-use of checksum in class 4, use of transport
different transport connections, while maintaining the order of
expedited data transfer service);
TPDUs for a given transport connection compatible with the
- alternative protocol class(es);
protocol operation.
- acknowledge time;
A valid set of concatenated TPDUs may contain
- throughput (proposed);
a) any number of TPDUs from the following list : AK, EA,
- residual error rate (proposed);
RJ, ER, DC TPDUs, provided that these TPDUs come from
- priority (proposed);
different transport connections;
- transit delay (proposed);
b) no more than one TPDU from the following list : CR,
- reassignment time;
DR, CC, DT, ED TPDUs; if this TPDU is present, it shall be
placed last in the set of concatenated TPDUs. - user data:
ISO/IEC 8073 : 1988 (E)
b) CCTPDU initiator shall acknowledge the CC TPDU as defined in table 5
(see 6.13)
CDT;
DST-REF;
When the network expedited variant of the expedited data
transfer (see 6.11) has been agreed (possible in class 1 only),
SRC-REF;
the responder shall not send an ED TPDU before the CC TPDU
CLASS and OPTIONS (selected);
is acknowledged.
calling TSAP-ID;
:
The following information is exchanged
called TSAP-ID;
TPDU size (selected);
a) references : Each transport entity chooses a reference
to be used by the peer entity which is 16 bits long and which
protection parameter;
is arbitrary under the following restrictions :
checksum;
additional option selection (selected); 1) it shall not already be in use nor frozen (see 6.181,
acknowledge time;
2) it shall not be zero.
throughput (selected);
This mechanism is symmetrical and provides identification
residual error rate (selected);
of the transport connection independent of the network
priority (selected);
e-
connection. The range of references used for transport con-
-
nections, in a given transport entity, is a local matter.
transit delay (selected);
user data.
b) calling and called TSAP-IDs (optional) : when either
network address unambiguously defines the transport
address this information may be omitted.
6.5.4 Procedure
initial credit : Only relevant for classes which include
c)
A transport connection is established by means of one
the explicit flow control function.
transport entity (the initiator) transmitting a CR TPDU to the
other transport entity (the responder), which replies with a CC
d) user data : Not available if class O is the preferred class
TPDU.
(see the note). Up to 32 octets in other classes.
Before sending the CR TPDU, the initiator assigns the transport
NOTE - If class O is a valid response according to table 3, inclusion
connection being created to one (or more if the splitting pro-
of user data in the CR TPDU may cause the responding entity to
cedure is being used) network connection(s). It is this set of
refuse the connection (for example if it only supports class O).
network connections over which the TPDUs are sent.
e) acknowledgement time : Only in class 4.
NOTE - Even if the initiator assigns the transport connection to more
than one network connection, all the CR TPDUs (if repeated) or DR
f) checksum parameter : Only in class 4.
TPDUis) with DST-REF set to zero which are sent prior to the receipt
of the CC TPDU shall be sent on the same network connection, unless
g) protection parameter. This parameter and its semantics
an N-DISCONNECT indication is received. (This is necessary because
are user defined.
the remote entity may not support class 4 and therefore may not
recognize splitting.) If the initiator has made other assignments, it will
The following negotiations take place :
use them only after receipt of a class 4 CC TPDU (see also the splitting
procedure 6.23).
h) protocol class : The initiator shall propose a preferred
class and may propose any number of alternative classes
During this exchange, all information and parameters needed
which permit a valid response as defined in table 3. The
for the transport entities to operate shall be exchanged or
initiator should assume when it sends the CR TPDU that its
negotiated.
preferred class will be agreed to, and commence the pro-
cedures associated with that class, except that if class O or
NOTE - Except in class 4, it is recommended that the initiator starts an
class 1 is an alternative class, multiplexing shall not com-
optional timer TS1 at the time the CR TPDU is sent. This timer should
mence until a CC TPDU selecting the use of classes 2,3 or 4
be stopped when the connection is considered as accepted or refused
or unsuccessful. If the timer expires, the initiator should reset or
has been received.
disconnect the network connection and, in classes 1 and 3, freeze the
reference (see 6.18). For all other transport connection(s) multiplexed
NOTE - This means, for example, that when the preferred class
on the same network connection the procedures for reset or discon-
includes resynchronization (see 6.14) the resynchronization will
nect as appropriate should be followed.
occur if a reset is signalled during connection establishment.
When an unexpected duplicated CR TPDU is received (with
The responder shall select one class defined in table 3 as a
class 4 as preferred class) it shall be ignored in classes O, 1, 2 valid response corresponding to the preferred class and to
and 3 and a CC TPDU shall be returned in class 4.
the class(es), if any, contained in the alternative class
parameter of the CR TPDU. It shall indicate the selected
After receiving the CC TPDU for a class which includes the pro- class in the CC TPDU and shall follow the procedures for
cedure for retention until acknowledgement of TPDUs the
the selected class.
ISO/IEC 8073 : 1988 (E)
Table 3 - Valid responses corresponding to the preferred class and any alternative class proposed in the CR TPDU
t) reassignment time parameter : This indicates the time
If the preferred class is not selected, then on receipt of the
CC TPDU the initiator shall adjust its operation according to for which the initiator will persist in following the reassign-
ment after failure procedure.
the procedures of the selected class.
NOTES
The negotiation rules for the options are such that the initiator
may propose either to use or not to use the option. The
1 The valid responses indicated in table 3 result from both explicit
negotiation, whereby each of the classes proposed is a valid responder may either accept the proposed choice or select an
response, and implicit negotiation whereby
alternative choice as defined in table 4.
a) if class 3 or 4 is proposed then class 2 is a valid response;
When a parameter [which is valid for the proposed class(es)l is
b) if class 1 is proposed then class O is a valid response.
absent and a default value is defined in this International Stan-
2 Negotiation from class 2 to class 1 and from any class to an
dard, this is equivalent to the presence of the parameter with
higher-numbered class is not valid.
the default value.
3 Redundant combinations are not a protocol error.
In class 2, whenever a transport entity requests or agrees to the
j) TPDU size : The initiator may propose a maximum size transport expedited data transfer service or to the use of
for TPDUs, and the responder may accept this value or re-
extended formats, it shall also request or agree (respectively) to
spond with any value between 128 and the proposed value
the use of explicit flow control.
in the set of values availabl
...