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+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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+                                                                [Page 1]
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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:
+
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+          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.
+
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+
+    [ 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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+                                                                [Page 2]
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