This Recommendation defines a system for real-time video/audio transmission over an IP-based network. Three profiles are defined@ for video telephony@ SDTV video transmission@ and HDTV video transmission. The protocol of the system consists of session control and media transmission. Session control is based on the session initiation protocol (SIP)@ and for the use of SIP this Recommendation refers to [ITU-T J.366.4]. Several types of packet formats are defined for media transmission. With regard to codecs@ this Recommendation provides some mandatory codecs and some optional ones for each profile. The system equipped with the protocol specified here can be used for bidirectional applications such as video-enabled order wire as well as unidirectional applications such as electronic news gathering.