Sources
- Cisco Technotes: Understanding H.323 Gatekeepers
- Microsoft TechNet: H.323 Gatekeeper
- Packetizer: A Primer on the H.323 Series Standard
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An H.323 Gatekeeper serves the purpose of Call Admission Control and translation services from E.164 IDs (commonly a phone number) to IP addresses in an H.323 telephony network. Gatekeepers can be combined with a gateway function to proxy H.323 calls and are sometimes referred to as session border controllers (SBC). A gatekeeper can also deny access or limit the number of simultaneous connections to prevent network congestion.
H.323 endpoints are not required to register with a gatekeeper to be able to place point to point calls, but they are essential for any serious H.323 network to control call prefix routing and link capacities among other functions.
A typical H.323 Gatekeeper call flow for a successful call may look like:-
| | | | Endpoint A Endpoint B 1234 1123
The gatekeeper allows calls to be placed either: Directly between endpoints (Direct Endpoint Model), or Route the call signaling through itself (Gatekeeper Routed Model).
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