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36 Dialogic
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Global Call IP Technology Guide — November 2007
Dialogic Corporation
IP Overview
Endpoint Registration
An endpoint uses a process called registration to join the zone associated with a gatekeeper. In the
registration process, the endpoint informs the gatekeeper of its transport, alias addresses, and
endpoint type. Endpoints register with the gatekeeper identified in the gatekeeper discovery process
described above. Registration can occur before any calls are made or periodically as necessary. An
endpoint sends an RRQ (registration request) message to perform registration and in return receives
an RCF (registration confirmation) or RRJ (registration reject) message.
Endpoint Deregistration
An endpoint may send an URQ (unregister request) in order to cancel registration. This enables an
endpoint to change the alias address associated with its transport address or vice versa. The
gatekeeper responds with an UCF (unregister confirm) or URJ (unregister reject) message.
The gatekeeper may also cancel an endpoint’s registration by sending a URQ (unregister request)
to the endpoint. The endpoint should respond with an UCF (unregister confirm) message. The
endpoint should then try to re-register with a gatekeeper, perhaps a new gatekeeper, prior to
initiating any calls.
Endpoint Location
An endpoint that has an alias address for another endpoint and would like to determine its contact
information may issue a LRQ (location request) message. The LRQ message may be sent to a
specific gatekeeper or multicast to the well-known discovery multicast address for gatekeepers.
The gatekeeper to which the endpoint to be located is registered will respond with an LCF (location
confirm) message. A gatekeeper that is not familiar with the requested endpoint will respond with
LRJ (location reject).
Admission, Bandwidth Change and Disengage
The endpoint and gatekeeper exchange messages to provide admission control and bandwidth
management functions. The ARQ (admission request) message specifies the requested call
bandwidth. The gatekeeper may reduce the requested call bandwidth in the ACF (admission
confirm) message. The ARQ message is also used for billing purposes, for example, a gatekeeper
may respond with an ACF message just in case the endpoint has an account so the call can be
charged. An endpoint or the gatekeeper may attempt to modify the call bandwidth during a call
using a BRQ (bandwidth change request) message. An endpoint will send a DRQ (disengage
request) message to the gatekeeper at the end of a call.
1.2.6 H.323 Call Scenario via a Gateway
While the call scenario described in Section 1.2.4, “Basic H.323 Call Scenario”, on page 32 is
useful for explaining the fundamentals of an H.323 call, it is not a realistic call scenario. Most
significantly, the IP addresses of both endpoints were defined to be known in the example, while
most Internet Service Providers (ISPs) allocate IP addresses to subscribers dynamically. This
section describes the fundamentals of a more realistic example that involves a gateway.