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IMP/Host and Host/IMP Protocol change (RFC0704)

IP.com Disclosure Number: IPCOM000003750D
Original Publication Date: 1975-Sep-15
Included in the Prior Art Database: 2000-Sep-13
Document File: 3 page(s) / 7K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

P.J. Santos: AUTHOR

Abstract

This note is a revision of RFC 687 and sketches the design of an expansion to the IMP/host and host/IMP protocol which will include among other things the possibility of addressing hosts on more than 63 IMPs. Our intention in this expansion is to correct certain existing limits without fundamental changes in the philosophy of the IMP/host protocol; i.e., while many issues which would represent fundamental changes to the IMP/host protocol are presently under discussion in the world-wide packet-switching community, we are not able to undertake massive fundamental changes on a time scale compatible with the short term needs for network improvement (e.g., already there are 62 IMPs).

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 36% of the total text.

Network Working Group Paul J. Santos, Jr. (BBN)

Request for Comments 704 Sept 1975

NIC #33490

IMP/Host and Host/IMP Protocol Change

This note is a revision of RFC 687 and sketches the design

of an expansion to the IMP/host and host/IMP protocol which will

include among other things the possibility of addressing hosts on

more than 63 IMPs. Our intention in this expansion is to correct

certain existing limits without fundamental changes in the

philosophy of the IMP/host protocol; i.e., while many issues

which would represent fundamental changes to the IMP/host

protocol are presently under discussion in the world-wide

packet-switching community, we are not able to undertake massive

fundamental changes on a time scale compatible with the short

term needs for network improvement (e.g., already there are 62

IMPs).

The following paragraphs cover each of the major

characteristics of the expanded protocol. A knowledge of Section

3 of BBN Report 1822 is assumed. As is discussed below, the

expanded protocol is backwards compatible.

1. Expanded Leader Size. The leader will be expanded from two

to six 16-bit words. This will provide space for necessary field

expansions and additions. The expansion of the IMP/host

(host/IMP) leader to 96 bits from 32 causes word-boundary

problems for some hosts. To be able to deliver messages between

two hosts of which one is using the old protocol and the other

the new, without shifting the data in the IMP words, it is

necessary that the data (i.e. the first bit of the host/host

leader) start at an even multiple of 8-bit bytes from the

beginning of the entire message. On the other hand, each host

prefers (in fact requires, if no shifting is to be performed by

the host) that the combined host/IMP (IMP/host) and host/host

leaders occupy some integral number of machine words (defined as

the smallest sequence of bits that can be independently accessed

by the host/IMP interface). With a total host/IMP (IMP/host) and

host/host leader of 136 bits, only machines with 8-, 16-, 32-,

and 64-bit words will find the leader size suitable. To simplify

things for machines with other word lengths, a provision of the

protocol permits each host to tell its IMP a number of 16-bit

padding words to be inserted between the host/IMP (IMP/host) and

host/host leaders. This padding will be stripped off during

host-to-IMP processing by the IMP, and added in during

IMP-to-host processing. Thus, for instance, 24-bit machines can

specify one 16-bit word of padding, and 10- and 36-bit machines

can specify five 16-bit words.

2. Expanded Address field. The address fi...