Inter-Entity Communication - an experiment
RFC 441

Document Type RFC - Unknown (January 1973; No errata)
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Network Working Group                                       Bob Bressler
Request for Comments: 441                                     Bob Thomas
NIC 13773                                               January 19, 1973

               Inter-Entity Communication - An Experiment

   This note is an attempt to be a status report concerning an
   experiment based on the desire of users, at their consoles, to
   converse with one another, and perhaps to get some debugging
   assistance.  The user might ask: "who can I talk to"; "can I show him
   what I have done", and "can I let him run my program?"  Many time
   sharing systems provide capabilities such as these, within the bounds
   of their system.  Almost all systems have a "WHO" or "SYSTAT", many
   have commands like "LINK" or "TALK", and some support more esoteric
   capabilities like controlling another user's program.  At the last
   formal meeting of the Network Working Group, in October of 1971 at
   MIT, a group got together to talk about these features for Inter
   Entity Communications (IEC), and how they might be extended to span
   across Host boundaries.

   Subsequent development has proceeded in an ad hoc manner.  The
   general design philosophy paralleled that of TELNET in terms of
   having both server and user programs.  The server program would
   handle commands like "connect to user FOO", "where is user BAR", or
   "who is on your system?"  An initial implementation of a server and
   user was brought up at MIT-DMCG, using a completely arbitrary
   protocol.  Soon after that, in an effort to increase its usefulness,
   the protocol was modified to be compatible with that being used by
   the Resource Sharing Executive being developed at BBN-TENEX.

   The MIT user program used the concept of "ports" to help identify
   character streams entering and leaving an object.  A pictorial
   diagram follows (FIGURE 1) showing a user teletype, his job and two
   consultants with whom he is conversing.

Bressler & Thomas                                               [Page 1]
RFC 441                Inter-Entity Communication           January 1973

              +------+
              | USER |
              | TTY  |
              +------+
                |   |
   -------------|---|--------------+
                |   |              |               +-------+
        +------------------+       |               | HOST  |
        |     COMMAND      |       |               |   A   |
        |   INTERPRETER    |       |               +-------+
        +---+-+-------+-+--+       |                   |
        TTY |_|       |_| TTY      |                   |
    OUT-PORT ^         | IN-PORT   |                   |
             |         |           |                   |
             |         V           | +--------------+  |
                                 +-|-+              |  |
                            <----| |IN-PORT         |--+
                                 +-|-+              |
                                   | |  CONSULTANT  |
                                   | |     #1       |
                                 +-|-+              |
               I.E.C.         ---->| |OUT-PORT      |
                                 +-|-+              |
                                   | +--------------+
                                   |
                                   | +--------------+
                                 +-|-+              |
                            <----| |IN-PORT         |--+
                                 +-|-+              |  |
                                   | |  CONSULTANT  |  |
                                   | |     #2       |  |
                                 +-|-+              |  |
           ^          |     ---->| |OUT-PORT        |  |
           |          |          +-|-+              |  |
   JOB     |          V  JOB       | +--------------+  |
   IN-PORT+--+       +--+OUT-PORT  |                   |
     -----|--|-------|--|----------+                   |
     +----+  +-------+  +---------+                    |
     |                            |                 +------+
     |      USER     JOB          |                 | HOST |
                                                    |  B   |
                                                    +------+

   The user now has the option of opening or closing any of the ports he
   wishes.  While in conversation mode, he might turn off the ports
   leading to the JOB.  If he wished consultant 1 to control the job, he
   might turn off the input ports from his own TTY and from consultant
   2.

Bressler & Thomas                                               [Page 2]
RFC 441                Inter-Entity Communication           January 1973

   Towards this goal, the user interface provides the following set of
   commands:

   WHO         user supplies which host, and given a list of [user,
               teletype, jobs].

   WHERE       user supplies identification of another user, and program
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