IMP System Change Notification
Planning a major upgrade to the ARPANET's packet routers
McQuillan, J.M., "IMP System Change Notification", RFC 331, DOI 10.17487/RFC0331, April 1972, <https://www.rfc-editor.org/info/rfc331>.
@misc{rfc331,
series = {Request for Comments},
number = 331,
howpublished = {RFC 331},
publisher = {RFC Editor},
doi = {10.17487/RFC0331},
url = {https://www.rfc-editor.org/info/rfc331},
author = {J.M. McQuillan},
title = {{IMP System Change Notification}},
pagetotal = 1,
year = 1972,
month = apr,
} RFC text
Network Working Group J. McQuillan
RFC #331 BBN-NET
NIC #9924 19 April 1972
Category: B.1
IMP System Change Notification
We are planning to release IMPSYS 2600 on May 15, 1972, be- tween
12 noon and 3 p.m. E.D.T. As discussed at the March 16 seminar held
at BBN, this release constitutes a major change to the IMP program.
Because of the magnitude of the change, the system will be released on
an experimental basis. If problems develop, then the current system,
IMPSYS 2514, will be reloaded and the cutover for IMPSYS 2600 will be
rescheduled for some later time.
The actual transfer over to IMPSYS 2600 will require assis- tance
from site personnel, and we hereby request this assistance. A new
tape of IMPLOD 2600 will be mailed to all sites shortly, and the staff
at BBN will request each site in turn on May 15 to load the new IMPLOD
tape and will detail other procedures to follow thereafter. We prefer
that each site have someone who is familiar with IMP system operation
on hand at this time. At some sites, we may request additional
assistance from the computer operations staffs or programmers in the
case of any problems. We also advise site personnel to refrain from
scheduling produc- tion over the Network during the hours of
switchover, since unforeseen difficulties may arise.
It is anticipated that the Hosts will not see any first- order
effects from the switchover. Leader formats and message types are not
changed. On the other hand, the statistics package has been
extensively modified, and the NMC has been notified of these changes.
The Very Distant Host option will also be included in this new system
release, and it is expected to be activated for use about June 1. The
detailed changes to the IMP system will be described in a forthcoming
revision to BBN Report 1822.
Finally, your patience is requested if the new system causes
unforeseen problems.
JMcQ/jm
[ This RFC was put into machine readable form for entry ]
[ into the online RFC archives by BBN Corp. under the ]
[ direction of Alex McKenzie. 12/96 ]
AI ELI5
On this page
§1The IMPSYS 2600 Release
On April 19, 1972, Jim McQuillan of BBN announced that IMPSYS 2600, a major upgrade to the IMP (Interface Message Processor) software, would be released on May 15, 1972, between noon and 3 p.m. EDT. This constituted a major change to the core routing software of every IMP on the ARPANET. Because of the magnitude of the change, the system would be released on an experimental basis: if problems appeared, the current system (IMPSYS 2514) would be reloaded and the cutover would be rescheduled for a later time.
BBN said it would swap the software in the network's traffic routers on a specific day. If things went wrong, they could switch back.
§2What Sites Had to Do
The switchover required assistance from personnel at each ARPANET site. BBN would mail a new IMPLOD 2600 tape to each site and call them on May 15 to load it and follow detailed procedures. BBN preferred to have on-site personnel familiar with IMP operations present. In case of serious problems, BBN might request assistance from site computer operations staff or programmers. All sites were advised to refrain from scheduling production network traffic during the switchover window due to the risk of unforeseen difficulties.
Each site got a new tape in the mail and had to put it in their machine when BBN called. People were told not to plan important work that day.
§3What Would Change and What Wouldn't
The announcement emphasized that hosts would not see first-order effects from the switchover because leader formats and message types were not changed. However, the statistics package had been extensively modified, and the Network Measurement Center was notified of these changes. Additionally, the Very Distant Host option would be included in IMPSYS 2600 and was expected to be activated for use around June 1, 1972. Detailed technical changes would be described in a forthcoming revision to BBN Report 1822, the standard reference for IMP behavior.
The way computers talked to the routers didn't change, so they didn't need new code. But the routers would keep track of their work differently, and could soon talk to computers very far away.