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H.323. Chapter 10. H.323. H.323 is a standard to allow telephones on the public telephone network to talk to computers (terminals) connected to the Internet. Gateway – connects the Internet to the telephone network Gatekeeper – Server on the local area network. Like the SIP registrar server.
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H.323 Chapter 10
H.323 • H.323 is a standard to allow telephones on the public telephone network to talk to computers (terminals) connected to the Internet. • Gateway – connects the Internet to the telephone network • Gatekeeper – Server on the local area network. Like the SIP registrar server
Gateway • Connects the Internet to the telephone network • Gateway is a multi layer device that translates one protocol to another • In this case, it translates the telephone protocol to the Internet protocol
Scope of H.323 • Diagram p 231 • Codec
Gateway • H.323 gateway reflects the characteristics of a Switched Circuit Network endpoint and H.323 endpoint • Translates between audio, video and data transmission formats • Includes call setup and teardown on both IP network and Switched Circuit Network • Only required if interconnecting with the Switched Circuit Network
Gatekeeper • Provides pre-call and call-level control services to H.323 endpoints • Gatekeepers are logically separated from other network elements in H.323 environments • Address translation • Bandwidth control • Admissions control
H.323 Protocols • Control and Signaling – Q.931 – used for establishing and terminating connections • H.225 – registration with the gatekeeper • Media Control and Transport – Provides a reliable H.245 channel that carries media control messages
Registration, Discovery, Endpoint Location • Gatekeeper Discovery- manual or automatic process endpoints use to identify which gatekeeper to register with • Registration –Process that enables gateways, endpoints to join a zone and inform the gatekeeper of their IP and alias addresses • Endpoint Location – obtain contact information when only alias info is available
Call Control Signaling H.225 • Uses Q.931 Signaling messages • Reliable call control channel is created across the IP network on TCP port 1720 • This port initiates Q.931 call control messages for the purpose of connecting, maintaining and disconnecting calls
Media Control and Transport • H.245 – Handles end to end control messages. Establishes logical channels for transmission of audio, video, data, and control channel information • Opening and closing of logical channels, preference modes, and message control take place over this control channel
Media Transport • RTP – enables real-time, end-to-end delivery of interactive, audio, video and data over unicast or multicast networks. • RTCP – monitors data delivery as well as controls and identifies services • Media channel is created using UDP where RTP streams operate on an even port number and corresponding RCTP stream on the next higher odd port
H.3232 Call Flows • Speech calls between endpoints • P244, 246