1. Introduction, Motivation

There are two basic approaches which can be taken when "porting" ISO applications to TCP/IP ([RFC793],[RFC791]) and IPv6 [IPV6] environments. One approach is to port each individual application separately, developing local protocols on top of TCP. A second approach is based on the notion of layering the ISO Transport Service over TCP/IP. This approach solves the problem for all applications which use the ISO Transport Service. This document describes the second approach.

The protocol described in this memo is based on the observation that both the Internet Protocol Suite and the ISO Protocol Suite are layered systems. A key aspect of the layering principle is that of layer-independence. The concept of layer-independence means that if one preserves the services offered by a particular layer (the Service-Provider) then the Service-User at that layer is completely unaffected by changes in the underlying layers or by the protocol used within the layer.

This document defines a Transport Service which appears to be identical to the Services and Interfaces offered by the ISO Transport Service Definition [ISO8072], but which will in fact implement the ISO Transport Protocol [ISO8073] on top of TCP/IP (IPv4 or IPv6), rather than the ISO Network Service [ISO8348].

The basis of this document is STD35, RFC1006^std35 [RFC1006] written by Marshall T. Rose and Dwight E. Cass and it defines two transport classes of service. Transport Class 0 refines and supersedes the RFC1006^std35 protocol and is aimed at preserving the RFC1006^std35 installed base. Transport Class 2 defines a number of new features which are not provided in RFC1006^std35, such as independence of Normal and Expedited Data channels and Explicit Transport Disconnection. These new features are largely based on RFC1859 [RFC1859] and extend the applicability of RFC1006^std35 to new groups of applications.

This document specifies changes to the standards mentioned above and must be read in the context of the above mentioned standards. It will not be meaningful on its own.

The 'well known' TCP port 102 is reserved for hosts which implement the Protocol described in this document. Note that the Protocol does not mandate the use of TCP port 102 for all connections.