H.323 Gatekeeper

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. 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 H323 Gatekeeper call flow for a successful call may look like:
| |
Endpoint A Endpoint B 1234 1123

# Endpoint A dials 1123 from the system.
# Endpoint A sends ARQ (Admission Request) to the Gatekeeper.
# Gatekeeper returns ACF (Admission Confirmation) with IP address of endpoint B.
# Endpoint A sends Q.931 call setup messages to endpoint B.
# Endpoint B sends the Gatekeeper an ARQ, asking if it can answer call.
# Gatekeeper returns an ACF with IP address of endpoint A.
# Endpoint B answers and sends Q.931 call setup messages to endpoint A.
# IRR sent to Gatekeeper from both endpoints.
# Either endpoint disconnects the call by sending a DRQ (Disconnect Request) to the Gatekeeper.
# Gatekeeper sends a DCF (Disconnect Confirmation) to both endpoints.

ee also

* GnuGK
* Cisco IOS release version 11.3(2)NA and 12.0(3)T
* Cisco Multimedia Conference Manager (MCM)