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Some changes to the IMP and the IMP/Host interface (RFC0660)

IP.com Disclosure Number: IPCOM000003719D
Original Publication Date: 1974-Oct-23
Included in the Prior Art Database: 2000-Sep-13
Document File: 2 page(s) / 5K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

D.C. Walden: AUTHOR

Abstract

In the next few weeks several changes will be made to the IMP software including changes to the IMP/Host software interface as specified in BBN Report No. 1822, Specifications for the Interconnection of a Host and an IMP. These changes come in four areas: a) decoupling of the message number sequences of Hosts; b) Host/Host access control; c) expansion of the message number window from four to eight; and d) provision for messages outside the normal message number mechanism. All changes are backward compatible with possible minor exceptions in timing.

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Network Working Group D. Walden (BBN-NET)

Request for Comments: 660 Oct 1974

NIC #31202

SOME CHANGES TO THE IMP AND THE IMP/HOST INTERFACE

In the next few weeks several changes will be made to the IMP

software including changes to the IMP/Host software interface

as specified in BBN Report No. 1822, Specifications for the

Interconnection of a Host and an IMP. These changes come in

four areas: a) decoupling of the message number sequences of

Hosts; b) Host/Host access control; c) expansion of the

message number window from four to eight; and d) provision for

messages outside the normal message number mechanism. All changes

are backward compatible with possible minor exceptions in timing.

a. Decoupling of the Host/Host message number sequences:

Since 1972 the IMP system has provided for exactly four

messages to be outstanding at a time between any pair of

IMPs, and thus, a total of only four messages between

all the possible pairs of Hosts on the two IMPs. Because

all the pairs of Hosts on the two IMPs have had to share

the four outstanding messages, it has been quite possible

for the various Hosts to interfere with each other. To

remove this possibility of interference, the IMP's

message number logic will soon be changed to allow a

separate message number sequence between each pair of Hosts.

To keep manageable the space required to maintain the

Host/Host message sequences above that presently are required

for the IMP/IMP message sequences, the Host/Host sequences

will be taken dynamically from a limited pool of possible

sequences. The pool will be sufficiently large to seldom

interfere with a pair of Hosts wishing to communicate. In

no case will Hosts be prevented from communicating. In

the event that the Hosts on an IMP desire to simultaneously

communicate with so many other Hosts that the pool would

be exhausted, the space in the pool is quickly multiplexed

in time among all the desired Host/Host conversations

so that none is stopped although all are possibly slowed.

b. Host/Host access control:

Upon instructions from ARPA, we will soon add a Host/Host

access control mechanism to the IMPs. Any pair of Hosts

wishing to communicate is checked (via bits in the IMP)

to verify that they have administrative permission to

communicate. This check normally is made whenever a pair

of Hosts attempts to communicate after not having

communicated for two minutes. If the pair of Hosts is

not allowed to communicate, a special type of Destination

Dead Message (sub-code 3) is returned to the source

Host. The default case initially will be to allow all

Hosts to communicate with each other.

-1-

c. Message number window.:

Once the message number sequences are on a Host/Host

rather than IMP/IMP basis, the number of messages that

will be permitted to be outstanding at a time between

a pair of H...