The Free On-line Dictionary of Computing (30 December 2018):

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.

   (2003-11-30)