H.323
The ITU-T standard for sending voice (audio) and video using IP on a LAN without QoS.
H.323 includes Q.931 for call setup, H.225 for call signalling, H.245 for exchanging terminal capabilities, RTP/RTCP for packet streaming, G.711/G.712 for CODECs, and several other protcols, many of which need to be negotiated to setup a simple voice call.
The complexity of H.323 has lead to the IETF proposing the simpler alternatives SIP and MGCP/Megaco.