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Connecting M.I.T (RFC0032)

IP.com Disclosure Number: IPCOM000003516D
Original Publication Date: 1970-Feb-05
Included in the Prior Art Database: 2000-Sep-13
Document File: 1 page(s) / 2K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

Computers to the ARPA Computer-To-Computer Communication Network. D. Vedder: AUTHOR

Abstract

Re: NWG/RFC's #28 and 29.

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 100% of the total text.

Network Working Group Jerry Cole, UCLA

Request for Comments: 32 February 5, 1970

SOME THOUGHTS ON SRI'S PROPOSED REAL TIME CLOCK

Re: NWG/RFC's #28 and 29.

The addition of a clock in one or more of the network HOST's seems to be

very desireable since it (or they) would allow user-oriented message

delay measurements. Our present network measurement facilities do not

include any internal HOST delays, and these delays may be an appreciable

portion of the total delay encountered by a HOST-to-HOST message

transmission. We may find that an extension of our "Trace" capabilities

to include internal HOST delays would be an appropriate mechanism for

utilizing such a clock. Such usage would require a clock at both the

source and the destination of the message, although such clocks would

not have to be particularly accurate nor synchronized. Other tests,

such as the absolute overall message delay from HOST A to HOST B would

require synchronization of the two clocks.

A reasonable specification for the SRI real-time clock would seem to

include a resolution of about 1 msec., an accuracy of about 1 part in

10E7 (so that two such clocks could maintain reasonable relative

accuracies over periods of many hours), and a range of about 24 hours.

A crystal controlled clock should easily meet these requirements at a

moderate cost.

The choice of the mechanism by which the HOST can read the clock appears

to be of concern also. The 1 msec. resolution may require that the

clock be entirely hardware (as opposed to a core location which would be

incremented at each clock pulse), and therefore the clock may require

some rather compli- cated interface circuitry.

At UCLA, we presently have two clocks on the Sigma 7, and one of these

has a resolution of about 2 msec. which might be usable for some

internal HOST measurements. However, it does not have the long term

accuracy for the absolute measurements mentioned above.

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