RFC209 - Host/IMP interface documentation

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　　Network Working Group B. Cosell
Request for Comments: 209 Bolt Beranek and Newman
NIC: 7187 13 August 1971

HOST/IMP Interface Documentation

On 25 June 1971 we put a new version of the IMP system, Version 2500,

up in the.network. Among other changes, the new system corrected the
problem of Hosts receiving spurious "Destination Dead" [Type 7]
messages. The correction involved making the IMP refuse to accept
any messages from its Host for about 30 seconds after the Host
indicated its intention to come alive. This delay has caused trouble
to a number of NCPs because they had imposed an upper limit on the
time an IMP may take to accept a message, and when that time was
exceeded the IMP was declared inoperative and the NCP shut itself
down, leaving the site personnel annoyed and perplexed.

We're sorry to have caused so much trouble, but we thought that the
new version modified no advertised property of the system. To
prevent misunderstandings of this type in the future, the IMP/Host
interface should be well documented, well understood and invariant.
The only way to set up and maintain such an interface is to presume
that BBN Report No. 1822 is complete and correct. We understand that
it is neither, but operating on the basis of this assumption is the
best way to force 1822 to improve. In our view, the Hosts should
proceed under the constraint that anything not specifically
guaranteed by 1822 does not exist and should not be used. If there
are problems using this approach, please don't "code around" the
problem or treat your IMP as a "black box" and extrapolate its
characteristics from a series of experiments. Instead, send your
comments and problems to the NCC at BBN, and we will fix the IMP
system, or 1822, whichever is necessary.

We are, at the moment, working n an update to 1822. It will reflect
the deletion of the "cease" mechanism [as per RFC#107].

We are also considering augmenting the IMP/Host protocol with a
mechanism to allow a Host to detect a change in the "version" of the
IMP system, and to provide the Hosts with status information as to
who is alive in the net.

[ This RFCwas put into machine readable form for entry ]
[ into the online RFCarchives by Ryan Kato 6/01]

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