1. I - INTRODUCTION

   In this document the Network Working Group at MIT Project MAC suggest
   modifications and extensions to the protocol specified by Carr,
   Crocker, and Cerf in a preprint of their 1970 SJCC paper and extended
   by Crocker in NWG/RFC 36.  This document broadly outlines our
   proposal but does not attempt to be a complete specification.  It is
   intended to be an indication of the type and extent of the protocol
   we think should be initially implemented.

   We agree with the basic concept of simplex communication between
   sockets having unique identifiers.  We propose the implementation of
   a slightly modified subset of the network commands specified in
   NWG/RFC36 plus the ERR command as specified by Harslem and Heafner in
   NWG/RFC 40.

   Given the basic objective of getting all ARPA contractors onto the
   network and talking to each other at the earliest possible date, we
   think that it is important to implement an initial protocol that is
   reasonably simple yet extendable while providing for the major
   initial uses of the network.  It should be a simple protocol so as to
   elicit the broadest possible support and to be easily implementable
   at all installations with a minimum of added software.

   While the protocol will evolve, the fundamentals of a protocol
   accepted and implemented by all installations are likely to prove
   very resistant to change.  Thus it is very important to make the
   initial protocol open-ended and flexible.  A simple basic protocol is
   more likely to succeed in this respect than a complicated one.  This
   does not preclude the existence of additional layers of protocol
   between several installations so long as the basic protocol remains
   supported.

   We feel that three facilities must be provided for in the initial
   protocol:

   1. Multi-path communication between two existing processes which know
      how to connect to each other.

   2. A standard way for a process to connect to the logger (logging
      process at a HOST) at a foreign HOST and request the creation of a
      user process.  (The login ritual may or may not be standardized.)

   3. A standard way for a newly created process to initiate pseudo-
      typewriter communication with the foreign process which requested
      its creation.

   The major differences between the protocol as proposed by Carr,
   Crocker, and Cerf and this proposal are the following:

   1. The dynamic reconnection strategy specified in Crocker's
      NWG/RFC 36 is reserved for future implementation.  We feel that
      its inclusion would unduly complicate the initial implementation
      of the protocol.  We outline a strategy for foreign process
      creation that does not require dynamic reconnection.  Nothing in
      this proposal precludes the implementation of dynamic reconnection
      at a later date.

   2. We propose that an "instance tag" be added to the socket
      identifier so as to separate sockets belonging to different
      processes of the same user coexisting at one HOST.

   3. The following NCP commands have been added:

      a. The ERR command specified in NWG/RFC 40 is included.

      b. BLK and RSM commands are presented as possible alternatives to
         the "cease on link" IMP command and SPD and RSM commands set
         forth in NWG/RFC 36.  Because these commands operate on socket
         connections rather than link numbers, they do not impede the
         implementation of socket connection multiplexing over a single
         link number, should that later prove desirable.

      c. An INT command that interrupts a process is specified.  We feel
         that it is highly important to be able to interrupt a process
         that may be engaged in unwanted computation or output.  To
         implement the interrupt as a special format within a normal
         message raises severe difficulties: the connection may be
         blocked when the interrupt is needed, and the NCP must scan
         each incoming message for an interrupt signal.

      d. An ECO echoing command to test communications between NCPs is
         included.

   4. Sockets are conceptualized as having several states, and these are
      related to conditions under which network requests may be queued.
      This differs from the unlimited queuing feature, which presents
      certain implementation difficulties.

   5. The protocol regarding creation of a foreign process and
      communication with it is removed to a separate User Control and
      Communication (UCC) protocol level and is more fully specified.