The purpose of the document is to examine whether accuracies achievable by currently available synchronization methods in IP networks are adequate to ensure end user's quality of service expectation for a particular multimedia service. This TSB will discuss the issues related to interstream synchronization when all the concerned media are offered using:

• IP networks from end-to-end;

•A combination of TDM and IP networks.

Services that will be covered, but not limited to:

• Video conferencing: uses video and voice;

• White boarding: uses data and voice.

When a multimedia service is offered in an IP-based network, the play-out mechanism involves demultiplexing of different media in end node and subsequent play-out of the media based on the timing information carried over by the media. Depending on this timing information, one media may precede the other resulting in user dissatisfaction. For each media, the timing relationship between different packets (intra-stream synchronization) is preserved by proper presentation at the end user in which play-out buffer management plays a crucial part. Size of the play-out buffer can be a fixed value or can be adaptively set based on one way delay measurement using timestamps.

This document gives an overview of synchronization methods by time stamping and the other means that are available to IP-based real-time applications and the effect of these methods on service performance as experienced by end user. However, actual implementation of time stamping is outside the scope of this TSB. The reference point at which inter-stream synchronization will be examined is considered to be at the interface of the end device involved, where the play-out buffers are normally located.