RFC 381 (rfc381) - Page 1 of 4

Three aids to improved network operation

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Network Working Group                                       J. McQuillan
Request for Comments: 381                                      D. Walden
NIC: 11151                                  Bolt Beranek and Newman Inc.
                                                            26 July 1972


                Three Aids To Improved Network Operation

1.  Scheduled Software Maintenance

   As the ARPA Network has grown larger, we have found it difficult to
   find times when necessary new software can be slipped into the
   network without disrupting anyone.  For instance, there is always
   intrasite traffic between the machines at MIT, and there is almost
   always traffic between the AMES TIP and IMP--the sun never sets on
   the ARPA Network.  To minimize unscheduled disruptions and to
   simultaneously let us do what we have to do, we propose to schedule 7
   A.M. - 8 A.M. eastern time every Tuesday as a time when the IMPs can
   be reloaded.  We will probably not use this period every Tuesday, but
   we do reserve this period every Tuesday.  The above period is in
   addition to the several hours a month already scheduled at each site
   for hardware preventative maintenance.

   Because a network user may not know when his machine is scheduled for
   maintenance or because he may forget and work through the Tuesday
   morning software period, we propose to generalize the IMP-Going-Down
   IMP-to-Host control message so it may be used to remind the user.
   This message (described in detail below) will contain information
   that the IMP is going down in m times five minutes, for n times 5
   minutes, for a given reason.  Hosts (and the TIP) should use this
   information to remind all their Network users that the IMP will be
   going down after the stated interval.

   Occasionally there is an emergency reason for restarting or reloading
   an IMP.  For instance, while three Hosts at a site are functioning
   well, one Host cannot communicate with the IMP.  This sort of
   situation sometimes requires the IMP to be restarted.  Such a restart
   will be preceded by several minutes by an IMP-Going-Down Message to
   allow working users to save their work in such a way that they can
   restart once the IMP is back up.

   In both of these cases, as well as cases where an IMP is performing
   so poorly that is must be shut down quickly, a type 2 IMP-to-HOST
   message will be transmitted to the HOST about 30 seconds before the
   IMP goes down.  Finally, of course, there may be occasions when the
   IMP crashes so quickly that no warning is given, but the IMP will
   never be intentionally shut down in this way.




Mc Quillan, et. al.
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