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Comments on IMP/Host Protocol changes (RFCs 687 and 690) (RFC0692) Disclosure Number: IPCOM000003740D
Original Publication Date: 1975-Jun-01
Included in the Prior Art Database: 2019-Feb-14
Document File: 2 page(s) / 2K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

S.M. Wolfe: AUTHOR

Related Documents

10.17487/RFC0692: DOI


A proposed solution to the problem of combined length of IMP and Host leaders; see also RFCs 696, 690 and 687.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 65% of the total text.

Network Working Group Stephen Wolfe RFC # 692 UCLA CCN NIC # 32734 June 20, 1975


Basically, the proposed set of changes in RFC 687 seems reasonable, as are the comments in RFC 690.

The major problem, as pointed out by Postel, is the change in the combined length of the IMP and Host leaders to a total of 120 bits, which is not a multiple of both 8 and 36 bits.

The suggested solution is to increase the length of the host to host protocol leader by 24 bits, creating a total length of 144 bits. The problem, however, is that the only way of compatibly changing this length would be to have the IMP either insert or delete the extra 24 bits when converting to/from the old format leader. The problems with this solution are obvious.

The better solution is to change the length of the new proposed IMP leader. I suggest 104 bits instead of 80 bits. The complaint that 104 is not a multiple of an IMP word is valid, but it should not be that difficult if the following rules are observed.

1. The last 8 bits are never used to convey information.

2. The network is not required to pass them from source to destination, or to return them to the source.

3. When sending messages of types other than zero, (irregular messages), the IMP is allowed to send either 96, 104 or 112 bits of data, the choice being at the IMP’s convenience.

4. Also, if desired, either 96 or 112 could be used as the new leader length for irregular messages.

It must be f...