|
Network Working Group Request for Comments: 32 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. 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. to include internal HOST delays would be an appropriate mechanism for utilizing such a clock. source and the destination of the message, although such clocks would not have to be particularly accurate nor synchronized. 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. 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. accuracy for the absolute measurements mentioned above. |
Jerry Cole, UCLA February 5, 1970 Our present network measurement facilities do not We may find that an extension of our "Trace" capabilities Such usage would require a clock at both the Other tests, The 1 msec. resolution may require that the However, it does not have the long term |
[Page 1]