Scheduled IMP Software Releases
BBN's reminder that IMPs may be reloaded on Tuesday mornings, and how hosts get warned.
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 ]
AI ELI5
On this page
§1Scheduling Reminder
The note reminds readers that the procedures suggested in RFC 381 for scheduling IMP software maintenance had been in effect for about two months. Two points needed re-emphasis.
A friendly reminder of the rules that were set up two months earlier.
§2The Tuesday Window and Warnings
First, BBN reserves the hour from 7 to 8 a.m. eastern time every Tuesday for reloading IMPs. It will probably not use the period every Tuesday, but it reserves it every Tuesday. This is in addition to the hardware preventive maintenance scheduled at each site.
Second, an IMP-Going-Down message is sent to all hosts at the site, giving the time, expected duration and reason. BBN tries to send it an hour before software releases and five to ten minutes before scheduled preventive maintenance, and notifies hosts when possible before unscheduled stops. Thirty seconds before the IMP goes down, a second message says it is going down immediately.
Tuesday early morning is set aside for restarts. You get a warning an hour before, and another just before the switch-off.
§3The IMP-Going-Down Message
The message is 32 bits. Bits 1 to 4 are all zero, bits 5 to 8 are 0010 and bits 9 to 16 are all zero. Bits 17 to 32 carry the details.
- 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 to 22: how soon the IMP is going down, in 5 minute units.
- Bits 23 to 32: how long it will be down, in 5 minute units.
The warning is a tiny coded note. Part of it says why, part says how soon, and part says how long.
| 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, 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. |