RFC 381 (rfc381) - Page 2 of 4

Three aids to improved network operation

RFC 381         Three Aids To Improved Network Operation    26 July 1972


2.  IMP-to-Host Communication

   There have long been complaints that the IMP-to-Host error messages
   were not precise enough or were just plain ambiguous.  In RFC #312 we
   proposed some additional error messages.  These and other IMP-to-Host
   message changes will be made on August 14, 1972 and we encourage
   Hosts to modify their NCP's as appropriate by then.  Unmodified NCPs
   will probably continue to work after this change, but each site
   should look into this question carefully.  The table below lists all
   the IMP-to-Host messages and clearly indicates the changes which will
   be made.

   Type      Old Meaning             New Meaning

    0        Regular Messages        Same

    1        Error without           Error in Leader of Host-to-
             identification          IMP Message
                                          Bits 31,32=00 - IMP's
                                          error flip-flop set on
                                          the first 32 bits of a
                                          Host-to-IMP message which
                                          the IMP therefore cannot
                                          identify
                                     Bits 31,32=01 - Host-to-IMP
                                          message too short (less
                                          than 32 bits)
                                     Bits 31,32=10 - illegal
                                          Host-to-IMP code

    2       IMP Going Down           IMP Going Down
                                          Bits 17-32 coded as follows:
                                          All bits zero - going down in
                                          30 sec.
                                     Bits 17,18=01 - scheduled
                                          hardware PM
                                     Bits 17,18=10 - scheduled
                                          software reload
                                     Bits 17,18=11 - emergency
                                          reload or restart
                                     Bits 19-22 - how soon the
                                          IMP is going down - in
                                          5 minute units
                                     Bits 23-32 - how long the IMP
                                          will be down - in 5
                                          minute units

    3       Blocked Link             Unassigned



Mc Quillan, et. al.