📄 rfc905.txt
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13.3.4 Variable Part (Octets 8 to p).................. 122
13.3.5 User Data (Octets p+1 to the end).............. 127
13.4 Connection Confirm (CC) TPDU..................... 128
13.4.1 Structure...................................... 128
13.4.2 LI............................................. 128
13.4.3 Fixed Part (Octets 2 to 7)..................... 128
13.4.4 Variable Part (Octet 8 to p)................... 129
13.4.5 User Data (Octets p+1 to the end).............. 129
13.5 Disonnect Request (DR) TPDU...................... 129
13.5.1 Structure...................................... 129
vii
13.5.2 LI............................................. 129
13.5.3 Fixed Part (Octets 2 to 7...................... 130
13.5.4 Variable Part (Octets 8 to p).................. 131
13.5.5 User Data (Octets p+1 to the end).............. 131
13.6 Disconnect Confirm (DC) TPDU..................... 132
13.6.1 Structure...................................... 132
13.6.2 LI............................................. 132
13.6.3 Fixed Part (Octets 2 to 6)..................... 132
13.6.4 Variable Part.................................. 133
13.7 Data (DT) TPDU................................... 133
13.7.1 Structure...................................... 133
13.7.2 LI............................................. 134
13.7.3 Fixed Part..................................... 134
13.7.4 Variable Part.................................. 135
13.7.5 User Data Field................................ 135
13.8 Expedited Data (ED) TPDU......................... 135
13.8.1 Structure...................................... 135
13.8.2 LI............................................. 136
13.8.3 Fixed Part..................................... 136
13.8.4 Variable Part.................................. 137
13.8.5 User Data Field................................ 137
13.9 Data Acknowledgement (AK) TPDU................... 137
13.9.1 Structure...................................... 137
13.9.2 LI............................................. 138
13.9.3 Fixed Part..................................... 138
13.9.4 Variable Part.................................. 139
13.10 Expedited Data Acknowledgement (EA) TPDU........ 140
13.10.1 Structure..................................... 140
13.10.2 LI............................................ 141
13.10.3 Fixed Part.................................... 141
13.10.4 Variable Part................................. 141
13.11 Reject (RJ) TPDU................................ 141
13.11.1 Structure..................................... 142
13.11.2 LI............................................ 142
13.11.3 Fixed Part.................................... 142
13.11.4 Variable Part................................. 143
13.12 TPDU Error (ER) TPDU............................ 143
13.12.1 Structure..................................... 143
13.12.2 LI............................................ 143
13.12.3 Fixed Part.................................... 144
13.12.4 Variable Part................................. 144
14 CONFORMANCE........................................ 145
14.1 ................................................. 145
viii
14.2 ................................................. 145
14.3 ................................................. 145
14.4 ................................................. 145
14.5 ................................................. 146
14.6 Claims of Conformance Shall State................ 146
ix
INTRODUCTION
The Transport Protocol Standard is one of a set of International
Standards produced to facilitate the interconnection of computer
systems. The set of standards covers the services and protocols
required to achieve such interconnection.
The Transport Protocol Standard is positioned with respect to
other related standards by the layers defined in the Reference
Model for Open Systems Interconnection (ISO 7498). It is most
closely related to, and lies within the field of application of
the Transport Service Standard (DP 8072). It also uses and makes
reference to the Network Service Standard (DP 8348), whose
provisions it assumes in order to accomplish the transport
protocol's aims. The interelationship of these standards is
depicted in figure 1.
-------------------------TRANSPORT SERVICE DEFINITION------------
Transport | --- Reference to aims --------------
Protocol |
Specification | --- Reference to assumptions -------
-------------------------NETWORK SERVICE DEFINITION--------------
Relationaship between Transport Protocol and adjacent services
Figure 1 .
The International Standard specifies a common encoding and a
number of classes of transport protocol procedures to be used
with different network qualities of service.
It is intended that the Transport Protocol should be simple but
general enough to cater for the total range of Network Service
qualities possible, without restricting future extensions.
The protocol is structured to give rise to classes of protocol
which are designed to minimize possible incompatibilities and
implementation costs.
1
The classes are selectable with respect to the Transport and
Network Services in providing the required quality of service for
the interconnection of two session entities (note that each class
provides a different set of functions for enhancement of service
qualities).
This protocol standard defines mechanisms that can be used to
optimize network tariffs and enhance the following qualities of
service:
a) different throughput rates;
b) different error rates;
c) integrity of data requirements;
d) reliability requirements.
It does not require an implementation to use all of these
mechanisms, nor does it define methods for measuring achieved
quality of service or criteria for deciding when to release
transport connections following quality of service degradation.
The primary aim of this International Standard is to provide a
set of rules for communication expressed in terms of the
procedures to be carried out by peer entities at the time of
communication. These rules for communication are intended to
provide a sound basis for development in order to serve a variety
of purposes:
a) as a guide for implementors and designers;
b) for use in the testing and procurement of equipment;
c) as part of an agreement for the admittance of systems into
the open systems environment;
d) as a refinement of the understanding of OSI.
It is expected that the initial users of the International
Standard will be designers and implementors of equipment and the
International Standard contains, in notes or in annexes, guidance
on the implementation of the procedures defined in the standard.
2
It should be noted that, as the number of valid protocol
sequences is very large, it is not possible with current
technology to verify that an implementation will operate the
protocol defined in this International Standard correctly under
all circumstances. It is possible by means of testing to
establish confidence that an implementation correctly operates
the protocol in a representative sample of circumstances. It is,
however, intended that this International Standard can be used in
circumstances where two implementations fail to communicate in
order to determine whether one or both have failed to operate the
protocol correctly.
This International Standard contains a section on conformance of
equipment claiming to implement the procedures in this
International Standard. Attention is drawn to the fact that the
standard does not contain any tests to demonstrate this
conformance.
The variations and options available within this International
Standard are essential to enable a Transport Service to be
provided for a wide variety of applications over a variety of
network qualities. Thus, a minimally conforming implementation
will not be suitable for use in all possible circumstances. It
is important, therefore, to qualify all references to this
International Standard with statements of the options provided or
required or with statements of the intended purpose of provision
or use.
1 SCOPE AND FIELD OF APPLICATION
1.1 This International Standard specifies:
a) five classes of procedures:
1) Class 0. Simple class;
2) Class 1. Basic error recovery class;
3) Class 2. Multiplexing class;
4) Class 3. Error recovery and multiplexing class;
5) Class 4. Error detection and recovery class,
3
for the connection oriented transfer of data and control
information from one transport entity to a peer transport
entity;
b) the means of negotiating the class of procedures to be
used by the transport entities;
c) the structure and encoding of the transport protocol data
units used for the transfer of data and control
information;
1.2 The procedures are defined in terms of:
a) the interactions between peer transport entities through
the exchange of transport protocol data units;
b) the interactions between a transport entity and the
transport service user in the same system through the
exchange of transport service primitives;
c) the interactions between a transport entity and the
network service provider through the exchange of network
service primitives.
These procedures are defined in the main text of the standard
supplemented by state tables in annex A.
1.3
These procedures are applicable to instances of communication
between systems which support the Transport Layer of the OSI
Reference Model and which wish to interconnect in an open systems
environment.
4
1.4
This International Standard also specifies conformance
requirements for systems implementing these procedures. It does
not contain tests which can be used to demonstrate this
conformance.
2 REFERENCES
ISO 7498 Information processing systems - Open systems
interconnection - Basic Reference Model
DP 8072 Information processing systems - Open systems
interconnection - Transport service definition
DP 8348 Information processing systems - Open systems
interconnection - Connection-oriented network service
definition.
5
SECTION ONE. GENERAL
3 DEFINITIONS
NOTE - The definitions contained in this clause make use of
abbreviations defined in clause 4.
3.1
This International Standard is based on the concepts developed in
the Reference Model for Open Systems Interconnection (DIS 7498)
and makes use of the following terms defined in that standard:
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