Network Working Group                        John M. McQuillan
Request for Comments # 406                   Bolt Beranek and Newman
NIC # 12111                                  10 October 1972
Categories B.1
Updates RFC # 381

                    Scheduled IMP Software Releases
                    -------------------------------

     This note is a reminder that the procedures suggested in
RFC # 381 for scheduling IMP software maintenance have now
been in effect for a period of about two months.  Two points
apparently require re-emphasis:

     1)   We reserve the hour from 7 to 8 a.m. eastern time
every Tuesday as the time when IMPs can be reloaded.  We will
probably not use this period every Tuesday, but we do reserve
this period every Tuesday.  The software maintenance time period
is in addition to the hardware preventive maintenance scheduled
at each site.

     2)   We now send an IMP - Going - Down message to all
the Hosts at the site which contains information on the time
that the IMP is going down, the expected duration, and the
reason.  We try to send out this message an hour before soft-
ware releases, and five to ten minutes before scheduled pre-
ventive maintenance.  Further, we will also notify the Hosts
at a site, whenever possible, when it is necessary to stop the
IMP on an unscheduled basis.  Finally, 30 seconds before the

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IMP goes down, a second IMP - Going - Down message will be
sent to the Hosts informing them that the IMP is going down
immediately.  The format of the IMP - Going - Down message
is as follows:

bits 1 - 4  -  all zero

bits 5 - 8  -  0010

bits 9 - 16 -  all zero

bits 17 - 32 -  coded as follows:

          All bits zero - going down in 30 seconds

          Bits 17, 18 = 01 - scheduled hardware PM

          Bits 17, 18 = 10 - scheduled software reload

          Bits 17, 18 = 11 - emergency reload on 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.

    [ This RFC was put into machine readable form for entry ]
    [ into the online RFC archives by BBN Corp. under the   ]
    [ direction of Alex McKenzie.                      1/97 ]

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