rfc2126.txt

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Network Working Group                                     Y. Pouffary
Request for Comments: 2126              Digital Equipment Corporation
Category: Standards Track                                    A. Young
                                                     ISODE Consortium
                                                           March 1997


               ISO Transport Service on top of TCP (ITOT)

Status of the Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document is a revision to STD35, RFC1006 written by Marshall T.
   Rose and Dwight E. Cass. Since the release of RFC1006 in May 1987,
   much experience has been gained in using ISO transport services on
   top of TCP. This document refines the protocol and will eventually
   supersede RFC1006.

   This document describes the mechanism to allow ISO Transport Services
   to run over TCP over IPv4 or IPv6. It also defines a number of new
   features, which are not provided in RFC1006.

   The goal of this version is to minimise the number of changes to
   RFC1006 and ISO 8073 transport protocol definitions, while maximising
   performance, extending its applicability and protecting the installed
   base of RFC1006 users.

Table of Contents

   1. Introduction, Motivation.....................................2
   2. The Model....................................................3
   2.1 ISO Transport Model.........................................3
   2.2 ISO Transport over TCP (ITOT) Model.........................4
   2.3 Overview of Protocol and Service............................5
   3 Service Definition............................................5
   3.1 Transport Service Definition................................5
   3.1.1 Transport Service Definition Primitives...................6
   3.2 Network Service Definition..................................7
   3.2.1 ISO 8348 CONS primitives..................................7
   3.2.2 TCP Service primitives....................................8
   3.2.3 Mapping TCP as a Network Service Provider.................8



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   3.2.3.1 Network Connection Establishment........................8
   3.2.3.2 Network Data Transfer...................................9
   3.2.3.3 Network Connection Release.............................10
   4. Transport Protocol Specification............................10
   4.1 Class 0 over TCP...........................................10
   4.1.1 Connection Establishment.................................11
   4.1.2 Data Transfer............................................11
   4.1.3 Connection Release.......................................11
   4.2 Class 2 over TCP...........................................12
   4.2.1 Connection Establishment.................................12
   4.2.2 Data Transfer............................................13
   4.2.3 Connection Release.......................................15
   4.3 TPKT Packet Format.........................................15
   5. Address representations.....................................16
   5.1 String representation of ITOT access point addresses.......17
   5.2 OSI Network Address encoding...............................17
   6. Notes to Implementors.......................................17
   6.1 TCP Connection Establishment...............................17
   6.2 TCP Data transfer..........................................17
   6.3 Class negotiation..........................................18
   6.4 Default maximum TPDU size..................................18
   6.5 Class 0 TPDU bit encoding..................................18
   6.6 Class 2 Options............................................19
   6.7 Class 2 Expedited Data Acknowledgement.....................21
   6.8 Class 2 Normal Data and Expedited Data handling............21
   6.9 Class 2 Forward Connection procedure.......................22
   6.10 TPKT......................................................22
   7. Rationale - Interoperability with RFC1006...................22
   8. Security Considerations.....................................23
   Acknowledgements...............................................23
   References.....................................................23
   Authors' Addresses.............................................25

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



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   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 [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 protocol and is aimed at preserving the RFC1006 installed
   base.  Transport Class 2 defines a number of new features which are
   not provided in RFC1006, 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 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.

2. The Model

   This section describes the differences between the model used by the
   ISO Transport and that described in this document.

2.1 ISO Transport Model

   The ISO 8072 standard describes the ISO Transport Service Definition
   (TS).  The ISO Transport Service Definition describes the services
   offered by the Transport Service Provider and the interfaces used to
   access these services.

   The ISO 8073 standard describes the ISO Transport Protocol
   Specification (TP).  The ISO Transport Protocol specifies common
   encoding rules and a number of classes of transport protocol
   procedure which can be used with different network Quality of
   Service.





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   The ISO 8348 standard describes the ISO Network Service Definition
   (NS).  The ISO Network Service Definition describes the services
   offered by the network service Provider and the interfaces used to
   access these services.

   The ISO Network Service specifies two type of service:

   - Connection Oriented Network Service (CONS)

   - ConnectionLess Network Service (CLNS)

   The ISO Transport Protocol specifies five classes of procedures when
   operating over CONS and one class of procedure when operating over
   CLNS.

   The relationship of these ISO standards is illustrated below:

            Transport Service User
              |
              |-ISO Transport Service Definition [ISO8072]
              |
         +--------------------------------------------------+
         |  Transport Service Provider                      |
         |  ISO Transport Protocol Specification [ISO8073]  |
         +--------------------------------------------------+
              |
              |-ISO Network Service Definition [ISO8348]
              |

2.2 ISO Transport over TCP (ITOT) Model

   This document defines a model which provides ISO Transport Service,
   with minor extensions, running over TCP.

   The ISO 8072 Transport Service is supported with minor modifications.
   See section 3.1.

   The ISO 8073 Transport Protocol with some modifications is used to
   provide the modified Transport Service.

   The Transmission Control Protocol is used in place of the ISO 8348 to
   provide a CONS like service. See section 4.

   This document specifies a simple encapsulation mechanism between the
   modified ISO 8073 Transport Protocol and the TCP.






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   ISO 8073 Transport Protocol specifies five classes when operating
   over ISO 8348 CONS. This document specifies how to operate class 0
   and 2 over TCP. This document does not prevent use of other classes
   from operating over TCP, but their specification is beyond the scope
   of this document.

   The relationship of these standards is illustrated below:

            Transport Service User
              |
              |-ISO Transport Service (modified)
              |
         +--------------------------------------------------+
         |  Transport Service Provider                      |
         |  ISO Transport Protocol (modified) Specification |
         +--------------------------------------------------+
              |
              |-TCP as a Connection Oriented Network Service
              |

2.3 Overview of Protocol and Service

   This document defines use of the ISO Transport Protocol (with some
   extensions) running over TCP. Two variants of the protocol are
   defined, "Class 0 over TCP" and "Class 2 over TCP", which are based
   closely on the ISO Transport Class 0 and 2 Protocol.

   Section 3 defines the Service offered to the Transport User by this
   protocol, and shows the differences from the ISO Transport Service.
   The mapping between the Service primitives in the ISO Network Service
   and TCP are defined. Section 4 defines the Transport Protocol.

3 Service Definition

   This section describes the Transport Service offered to the Transport
   User.  It also defines the mapping between the Network Service
   Definition and the TCP Service Definition.

3.1 Transport Service Definition

   ISO 8072 Transport Service is supported with the following
   extensions:

   - Use of Quality of Service parameter is not defined

   - Access to Non-disruptive Transport Disconnection





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3.1.1 Transport Service Definition Primitives

   Information is transferred to and from the TS-User in the Transport
   Service primitives listed below:

   Actions

      T-CONNECT.REQUEST
         - a TS-User indicates that it wants to establish transport
           connection

      T-CONNECT.RESPONSE
         - a TS-User indicates that it will honour the request

      T-DISCONNECT.REQUEST
         - a TS-User indicates that the transport connection is to
           be closed

      T-DATA.REQUEST
         - a TS-User sends data

      T-EXPEDITED DATA.REQUEST
         - a TS-User sends "expedited" data

   Events

      T-CONNECT.INDICATION
         - a TS-User is notified that a transport connection
           establishment is in progress

      T-CONNECT.CONFIRMATION
         - a TS-User is notified that the transport connection has been
           established

      T-DISCONNECT.INDICATION
         - a TS-User is notified that the transport connection is closed

      T-DATA.INDICATION
         - a TS-User is notified that data can be read from the transport
              connection

      T-EXPEDITED_DATA.INDICATION
         - a TS-User is notified that expedited data can be read from
           the transport connection







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3.2 Network Service Definition

   This section describes how TCP is used to provide ISO 8348 CONS.

3.2.1 ISO 8348 CONS primitives

   Information is transferred to and from the NS-provider in the Network
   Service Primitives listed below: