ISO Transport Protocol specification
RFC 892

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Network Working Group                                   ISO
Request for Comments:  892                              December 1983

                     ISO Transport Protocol Specification

This document is distributed as an RFC for information only.
It does not specify a standard for the ARPA Internet.

Note:  This document appeared in:

ISO/TC97/SC16/WG6.  Information Processing Systems - Open Systems
    Interconnection - Transport Protocol Specification.  Computer
    Communication Review 12, 3-4 (July/October 1982), pp.  24-67.

and differs from it only in format.

Table of Contents

0.   Introduction
1.   Scope and Field of Application
2.   References

Section One - General

3.   Definitions
4.   Symbols and Abbreviations
5.   Overview

     5.1  Service provided by the transport layer
     5.2  Service assumed from the network layer
     5.3  Functions of the transport layer
     5.4  Model of the transport layer

Section Two - Transport Protocol Specification

6.   Protocol Mechanisms
     
     6.1  Assignment to network connection
     6.2  Transport protocol data unit (TPDU) transfer
     6.3  Data TPDU length and segmenting
     6.4  Concatenation and separation
     6.5  Connection establishment
     6.6  Connection refusal
     6.7  Release
     6.8  Implicit termination
     6.9  Spurious disconnect
     6.10 Data TPDU numbering
     6.11 Expedited data transfer
     6.12 Reassignment
     6.13 Reassignment after failure


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     6.14 Retention until acknowledgement of TPDUs
     6.15 Resynchronization
     6.16 Multiplexing and demultiplexing
     6.17 Explicit flow control
     6.18 Checksum
     6.19 Frozen references
     6.20 Retransmission on timeout
     6.21 Resequencing
     6.22 Inactivity control
     6.23 Treatment of protocol errors
     6.24 Splitting and recombining

7.   Protocol Classes
     7.0  Protocol description of class 0:  simple class
     7.1  Protocol description of class 1:  basic error recovery class
     7.2  Protocol description of class 2:  multiplexing class
     7.3  Protocol description of class 3:  error recovery and multiplexing
                                            class
     7.4  Protocol description of class 4:  error detection and recovery class

8.   Encoding

     8.1  Summary
     8.2  Structure
     8.3  Connection Request (CR)
     8.4  Connection Confirm (CC)
     8.5  Disconnect Request (DR)
     8.6  Disconnect Confirm (DC)
     8.7  Data (DT
     8.8  Expedited Data (ED)
     8.9  Data Acknowledgement (AK)
     8.10 Expedited Data Acknowledgement (EA)
     8.11 Reject (RJ)
     8.12 TPDU Error (ERR)

Section Three  -  Conformance

9.   Conformance

0.   Introduction

        The Transport Protocol Standard is one of a set of International
Standards produced to facilitate the interconection 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


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Service Standard (DP aaaa).  It also uses and makes reference to the
Network Service Standard (DP bbbb), whose provisions it assumes in
order to accomplish the transport protocol's aims.  The
interrelationship of these standards is depicted in Figure 1.

-----------------------------------TRANSPORT SERVICE DEFINITION-----

 Transport                --Reference to aims---------------
 Protocol
 Specification            --Reference to assumptions--------

------------------------------------NETWORK SERVICE DEFINITION------

Figure 1  -  Relationship between the transport protocol and adjacent
             services

        The 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.

        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 is concerned with optimisation of network
tariffs and the following qualities of service:

     a)  different throughput rates;