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Network Time Synchronization Measurement and Accuracy

This article discusses the measurement and accuracy of network time synchronization. It covers the setup of the measurement, the synchronization of clocks, and the calculation of one-way delay. The article also explores the options for evaluating the accuracy of the synchronization method.

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Network Time Synchronization Measurement and Accuracy

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  1. One-way DelayMeasurement and Accuracy of the Network Time Synchronization Vladimir Smotlacha vs@cesnet.cz TF-NGN, April 2002

  2. Measurement of the Accuracy • local clock of workstation is synchronized to (far) time server by a method, which is tested • workstation is provided by PPS (Pulse Per Second) signal • timestamp of each PPS is evaluated • sub-second part of timestamp is actual offset of local clock

  3. Setup of the Measurement Time Synchronized server -------- network --------- box <--- PPS

  4. Current Results

  5. accuracy of NTP client client: Cesnet server: Heanet Current Results II

  6. OWD Measurement • two workstation: traffic generator and receiver • clock synchronization • time • frequency • clock synchronization accuracy - limiting factor for one-way measurement

  7. Organization of Measurement • boxes A and B synchronized to NTP server(s) • OWD = the difference between both timestamps • option: calculation of exact OWD if both A and B are supplied by PPS • option: comparison with RIPE TTM results, if RIPE box is available

  8. OWD Measurement Setup I + II NTP_ A NTP_B | | Box_A ----- network ----- Box_B NTP_A | Box_A ----- network ----- Box_B ( <-- PPS )

  9. OWD Measurement Setup III NTP_A ----- network ----- NTP_B | | institute A netw. institute B netw. | | NTP_A_sec NTP_B_sec | | (PPS --> ) Box_A Box_B ( <-- PPS)

  10. Box Specification • at least Pentium 120, Pentium II preferred • Linux kernel 2.4.16 with nanokernel patch • NTP package (4.1.71) • Rude/Crude 5.0 or 6.0 • PPS available at DCD pin of serial port

  11. Plans • setup boxes for OWD measurement • test commercial systems - NetIQ, IPANEMA • compare our method with others available (NetIQ, IPANEMA, RIPE TTM)

  12. Participants • HEAnet (Ireland) • GARR (Italy) • FOKUS (Gremany) • CESNET (Czech Republic) • cooperation with RIPE TTM

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