Proposal for Technical Assessment of Synchronization Methods in IP Networks from Quality of Experience Perspective Author: Radha Telikepalli Presented by: Roger Britt Organization: Nortel Networks Date: 4 th May, 2004

TR Where is Synchronization required in IP world? Real time media and/or interacting with TDM –Time stamps determine buffer play-out delays in the end device Single media –Setting of adaptive jitter buffer in the end devices Multiple Media where inter stream synchronziation is important –Example: lip syncing between audio and video, audio can be TDM based Operations, administration and management –Call processing and billing

TR IP based Services TDMoIP or Circuit Emulation over IP –Connects existing TDM islands using IP network –Synchronization requirements are the same as in TDM world Currently defined at ITU-T and ANSI T1 standard bodies VoIP –TR uses this acronym to represent voice and multimedia services offered over IP and/or TDM networks –Uses time stamp based synchronization methods

TR RTP based Media RTP header carries timestamps –Represents sampling instant of a data packet Generated by a sampling clock at the sender Used by the receiver to remove packet jitter –Multiple media have random offsets and use different sampling clocks RTP uses RTCP to get feedback on data distribution quality –RTP generates RTCP sender report for each RTP stream Number of packets sent in the stream Number of bytes sent Timestamp pairs of RTP and a real time clock/absolute time Real time clock –Based on time stamps –Gives absolute time with reference to UTC Buffer play-out delays depends on time stamp pairs in RTCP Sender reports

TR Buffer Play-out used in Multimedia service Incoming packets DeMUXDeMUX Depacketizer Synchronization agent Playout Delay adaptation in required format Depacketizer in required format Quality of Experience of an end user depends on play-out delays

TR Typical Network Scenarios used for Multimedia Services IP TDM  Synchronization is based on time stamps  Media synchronization depends on the accuracy of time stamps  IP network uses synchronization based on time stamps  TDM uses traditional hierarchical synchronization  Media synchronization depends on reference clocks used and relative accuracies of the methods followed in IP and TDM networks

TR Proposal A TSB should be developed to report accuracy of available synchronization methods in IP and requirements for inter-stream synchronization at the end user. The purpose of the document would be to assess current synchronization methods to support multimedia services.