RFC 1 (rfc1) - Page 2 of 11

Host Software

RFC 1                        Host Software                 7 April 1969


 IV. Initial Experiments

     Experiment One

     Experiment Two

Introduction

   The software for the ARPA Network exists partly in the IMPs and
   partly in the respective HOSTs.  BB&N has specified the software of
   the IMPs and it is the responsibility of the HOST groups to agree on
   HOST software.

   During the summer of 1968, representatives from the initial four
   sites met several times to discuss the HOST software and initial
   experiments on the network.  There emerged from these meetings a
   working group of three, Steve Carr from Utah, Jeff Rulifson from SRI,
   and Steve Crocker of UCLA, who met during the fall and winter.  The
   most recent meeting was in the last week of March in Utah.  Also
   present was Bill Duvall of SRI who has recently started working with
   Jeff Rulifson.

   Somewhat independently, Gerard DeLoche of UCLA has been working on
   the HOST-IMP interface.

   I present here some of the tentative agreements reached and some of
   the open questions encountered.  Very little of what is here is firm
   and reactions are expected.

I.   A Summary of the IMP Software

Messages

   Information is transmitted from HOST to HOST in bundles called
   messages.  A message is any stream of not more than 8080 bits,
   together with its header.  The header is 16 bits and contains the
   following information:

           Destination     5 bits
           Link            8 bits
           Trace           1 bit
           Spare           2 bits

   The destination is the numerical code for the HOST to which the
   message should be sent.  The trace bit signals the IMPs to record
   status information about the message and send the information back to
   the NMC (Network Measurement Center, i.e., UCLA).  The spare bits are
   unused.



Crocker