H.323 is recommendation from the ITU telecommunication standardization sector.

H.323 standard addresses call signaling and control multimedia transport control and bandwidth control for point to point.

H.323 call signaling is based on the ITU – TRecommendation Q.931 protocol.

IP telephony into existing networks of ISDN based PBX system.

Within the content of H.323 an IP based PBX might be gatekeeper or other call control element.

It support Real time transfer of audio and video data over packet network like IP.

Most voice over (VOIP) application utilize H.323

H.323 supports call setup tear down and forwarding/transfer.

Architecture element of H.323 based system are terminals, multipoint control units (MCU) Gateway.

Different function of H.323 run over either TCP or UDP.

H.323 completes with the newer session initialization protocol (SIP)

Key feature of H.323 quality of service. (QoS). QoS technology allows real time prioritization and traffic management.

Traffic management constraints to be placed on best effort packet delievery system.

Real time protocol (RTP) and Real time control protocol (RTCP) with addition protocols for call signaling and data.