Jitter Definitions What is what ? Discussion Roman Krzanowski



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Jitter Definitions What is what ? Discussion

  • Roman Krzanowski

  • IETF Vancouver , CND

  • November 2005


What is the Problem ?

  • There are two operationalized definitions of jitter

    • IETF RFC based (RFC 3393)
      • Statistics on interpacket delay variation; usually implemented as the variation of the delay on consecutive packets
      • Also implemented by MEF
      • Used by most North American SP in SLAs definition
      • Used in RTP protocol
      • Used in Video buffer sizing
    • ITU definition (Y.1541, Y.1540)
      • Difference between the DV(99%)-DV(0%) over a sample set
        • This is one of the DV definitions but most strongly supported by the providers
    • Any other jitter metrics we should discuss ?
    • Note: several alternative definitions in IETF RFC and ITU Y.1450 exist; presented shorthand definitions are selected on the basis of operational implementations and they do not exhaust all the options specified in RFC and ITU documents


What is the Problem ?

  • European and Australasian providers support strongly ITU definition claiming that it is the only right one and the only needed one

  • My contention is that both are a bit different (see AT&T paper) telling us different things about network events; Thus, there is a place for both metrics with necessary understanding that both have specific applications, advantages and disadvantages



What I am proposing ?

  • Have a discussion on merits and limitations of two (maybe more) jitter metrics

    • Develop UC where specific metrics are applicable
    • Develop test cases/models demonstrating the uses and abuses of both metrics
  • Develop recommendations (best practices) on the use of both metrics for:

    • The monitoring of the network performance
      • Which metrics and why and how
        • For VoIP, Video, network buffer sizing
    • Measuring burstness of the network traffic for VoIP and Video applications
    • Sizing de-jitter buffers based on each measure
    • Diagnosing network events based on both jitter measures
  • Create a team to work with on this issue



Selected References

  • ITU SG-12. Analysis, measurement and modeling of Jitter. January 2003

  • ‘Standardized active measurements on Tier I active IP backbone’, IEEE Communications Magazine, June 2003

  • ITU Y.1540 (12/2002)

  • ITU- Y.1541 Oct, 2005. temp

  • ITU. Clarification to the IP packet delay variation definition in Y.1540 . Al. Morton

  • SAA Documentation. Cisco

  • Brix Documentation. Brix Networks

  • RFC 3393



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