Scheduled IMP Software Releases
A reminder of the IMP maintenance window and host warning messages.
McQuillan, J.M., "Scheduled IMP Software Releases", RFC 406, DOI 10.17487/RFC0406, October 1972, <https://www.rfc-editor.org/info/rfc406>.
@misc{rfc406,
series = {Request for Comments},
number = 406,
howpublished = {RFC 406},
publisher = {RFC Editor},
doi = {10.17487/RFC0406},
url = {https://www.rfc-editor.org/info/rfc406},
author = {J.M. McQuillan},
title = {{Scheduled IMP Software Releases}},
pagetotal = 2,
year = 1972,
month = oct,
} RFC text
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
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 ]
ISO Plain Language
On this page
§1The Scheduled Window
The note says the scheduling procedures proposed in RFC 381 had been in effect for about two months. BBN reserves 7 to 8 a.m. Eastern time every Tuesday for possible IMP software reloads, although the period may not be used every week.
This software maintenance time is separate from hardware preventive maintenance scheduled at each site.
One hour every Tuesday is reserved for IMP software reloads. BBN may not use the hour each week, and hardware maintenance is scheduled separately.
§2Advance and Final Notices
BBN sends an IMP-Going-Down message to all Hosts at a site with the time, expected duration and reason. BBN tries to send the notice an hour before software releases and five to ten minutes before scheduled preventive maintenance.
When possible, Hosts are also notified before an unscheduled stop. Thirty seconds before the IMP goes down, a second message says that the shutdown is immediate.
Hosts receive a notice with the expected timing, duration and reason. A second message arrives 30 seconds before shutdown.
§3Message Fields
The IMP-Going-Down message has 32 bits. Bits 1 through 4 are zero, bits 5 through 8 are 0010, and bits 9 through 16 are zero.
Bits 17 and 18 identify scheduled hardware maintenance, scheduled software reload or emergency reload on restart. Bits 19 through 22 say how soon the IMP will go down in 5-minute units; bits 23 through 32 give the expected downtime in 5-minute units. All bits zero means going down in 30 seconds.
The message uses fields for the reason, how soon the IMP will stop and how long it will be down. The time values use five-minute units, except for the all-zero signal that means 30 seconds.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
ZERO-A | Zero | 4 bits | Bits 1 to 4, all zero. | |
TYPE | Type | 4 bits | 0010 | Bits 5 to 8. |
ZERO-B | Zero | 1 byte | Bits 9 to 16, all zero. | |
REASON | Reason | 2 bits | Bits 17 and 18: 01 hardware PM, 10 software reload, 11 emergency reload. | |
SOON | How soon | 4 bits | Bits 19 to 22, in 5-minute units. | |
DURATION | Duration | 10 bits | Bits 23 to 32, in 5-minute units. |