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