H.323 Recommendation published by ITU Ties together a number of protocols to allow multimedia transmission through an unreliable packet-based network 1996: approved by ITU 2003: Version 5 H.323 Architecture H.323 Terminal Gateway Gatekeeper Multipoint Control Units (MCU)

H.323 Protocol Stack for VOIP

H.323 and Associated Recommendations

H.323 Control Protocols H.225 (RAS)- protocol between terminal and gatekeeper (if present) allows terminals to join/leave zone, request/return bandwidth, provide status updates, … H.245 (Call Control) - Media Control Protocol Allows terminals to negotiate connection parameters (codec, bit rate,..) Q.931 (Call Signalling) - Manages call setup and termination

H.323 Adapted to IP

H.323 Terminals

Supported Protocols and Integration Options (Cont.) Analog Phones ATASkinny Analog H.323 FAX ATA

Supported Protocols and Integration Options (Cont.) H.323 Connections PSTN WAN CME Vmail CallManager Cluster H.323 Recommended

Supported Protocols and Integration Options (Cont.) Gatekeeper WAN Register Extension number and/or E.164 number Register H.323 Register Extension number and/or E.164 number Register Cisco CME can register to a H.323 gatekeeper thereby ensuring the WAN is not oversubscribed

Translation Between Signaling and Call Control

H.323 Gatekeepers

RAS Messages

H.323 Basic Call Setup

Finding and Registering with a Gatekeeper

Call Flow with a Gatekeeper

Gatekeeper-Routed Call Signaling

Call Flow with Multiple Gatekeepers