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Collaboration, Voice & AV · Intermediate

H.323

An ITU-T umbrella standard for multimedia communication over packet networks, comprising H.225, H.245, RAS and codecs.

Definition

H.323 predates widespread SIP and defines terminals, gateways, gatekeepers and MCUs. Call setup uses H.225.0 (based on Q.931) on TCP 1720, capability negotiation and media channel opening use H.245, and gatekeeper registration and admission use RAS on UDP 1719. It remains in use for legacy video endpoints and some voice gateways but has largely been replaced by SIP.

Example

A legacy H.323 video endpoint registers with an Expressway acting as gatekeeper and is interworked to SIP for Webex meetings.

Exam tip

Know the components and ports: H.225 TCP 1720, RAS UDP 1719, H.245 dynamic TCP; and that it is peer-to-peer with optional gatekeeper.

Don't confuse it with

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