This document defines the functional characteristics and the requirements of the packet-switched Video Telephony (VT) services, sometimes also referred to as Multimedia Conversational Services (MCS). Video Telephony is defined as one-to-one video/speech communication capability. VT (MCS) should be used as a basis for multiparty multimedia conferencing, but this is out of scope for the initial document revision.

This initial effort is to be mindful of the continued development in subsequent phases of the following enhancements (without implying any relative priority):

• Interoperability support to other video telephony systems;

• Capability of multipoint communication.

Hence the following two phases in the development of video telephony are defined:

Phase 1: Development of basic one-on-one video telephony functionality (Subject to Stage 1 Revision 0)

Phase 2: Enhancement for support of other video telephony systems and multipoint communication (Subject to Stage 1 Revision A or later)