Proposed experiment with a Message Switching Protocol
RFC 333

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Network Working Group                                       Bob Bressler
Request for Comments: 333                           MIT/Dynamic Modeling
NIC # 9926                                                    Dan Murphy
Category: C9 (experimentation)                                 BBN/TENEX
Obsoletes: 62                                                Dave Walden
Updates: none                                                    BBN/IMP
                                                             15 May 1972

        A PROPOSED EXPERIMENT WITH A MESSAGE SWITCHING PROTOCOL

CONTENTS

   Introduction ..................................................  1
   Some Background ...............................................  2
   References ....................................................  3
   MSP Specification .............................................  4
   Issue .........................................................  8
   Message Header ................................................ 10
   Examples ...................................................... 15
   TELNET ........................................................ 16
   The Information Operator ...................................... 16
   Unique Port Numbers ........................................... 20
   Flow Chart .................................................... 23
   MSP Variations ................................................ 25
   Appendix ...................................................... 26

INTRODUCTION

   A message switching protocol (MSP) is a system whose function is to
   switch messages among its ports.

   For example, there is an implementation of an MSP in each Interface
   Message Processor.  We believe that the effective utilization of
   communications networks by computer operating systems will require a
   better understanding of MSPs.  In particular, we feel that Network
   Control Programs (NCPs), as they have been implemented on the ARPA
   Computer Network (ARPANET), do not adequately emphasize the
   communications aspects of networking -- i.e., they reflect a certain
   reluctance on the part of systems people to move away from what we
   term "the stream orientation".  We propose, as an aside the network
   development using the current NCPs, to rethink the design of NCP-
   level software beginning with a consideration of MSPs.

   The thrust of this note is to sketch how one would organize the
   lowest level host-host protocol in the ARPANET around MSPs and how
   this organization would affect the implementation of host software.

Bressler, et al.            Experimentation                     [Page 1]
RFC 333          MESSAGE SWITCHING PROTOCOL EXPERIMENT          May 1972

SOME BACKGROUND

   Over the past several weeks there has been considerable informal
   discussion about the possibility of implementing, on an experimental
   basis, in several of the ARPA Network Host Computers, NCPs which
   follow a protocol based on the concept of message switching rather
   than the concept of line switching (see the parenthetical sentence in
   the first paragraph of page 6 of NIC document 8246, Host/Host
   Protocol for the ARPA Network).  Party to this discussion have been
   Bob Bressler (MIT/Dynamic Modeling) Steve Crocker (ARPA), Will
   Crowther (BBN/IMP), Tom Knight (MIT/AI), Alex McKenzie (BBN/IMP), Bob
   Metcalfe (MIT/Dynamic Modeling), Dan Murphy (BBN/TENEX), Jon Postel
   (UCLA/NMC), and Dave Walden (BBN/IMP).

   Several interesting points and conclusions have been made during this
   discussion:

      1. Bressler has implemented a message switched interprocess
         communication system for the Dynamic Modeling PDP-10 and has
         extended it so it could be used for interprocess communication
         between processes in the Dynamic Modeling PDP-10 and the AI
         PDP-10.  He reports that it is something like an order of
         magnitude smaller than his NCP.

      2. Murphy has noted that a Host/Host protocol based on message
         switching could be implemented experimentally and run in
         parallel with the real Host/Host protocol using some of the
         links set aside for experimentation.  Further, Murphy has noted
         that if this experimental message switching protocol were
         implemented in TENEX, a number of (TENEX) sites could easily
         participate in the experiment.

      3. It is the consensus of the discussants that Bressler should
         take a crack at specifying a message switching protocol* and
         that if this specification looked relatively easy to implement,
         a serious attempt should be made by Murphy and Bressler to find
         the resources to implement the experimental protocol on the two
         BBN TENEX and the MIT Dynamic Modeling and AI machines.

      4. MSP was chosen as the acronym for Message Switching Protocol,
         and links 192-195 were reserved for use in an MSP experiment.

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