Chapter 4 – Gatekeeper Protocols
Multi-Tech Systems, Inc. MultiVOIP Gatekeeper User Guide
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Chapter 4 - Gatekeeper Protocols
H.323 is an umbrella standard that consists of many subordinate protocols. Three protocols, Q.931, H.225, and
H.245, are particularly relevant to Gatekeepers.
The Q.931 protocol pertains to the setup and teardown of call connections between network endpoints.
The H.225 Call Signaling Protocol pertains to Registration, Admission, and Status (RAS). (Note that RAS in
H.323 has nothing to do with the Remote Access Service that is used in ordinary TCP/IP networks.) H.323 RAS
messages are concerned with general participation on the network (registration), specific involvement in particular
calls between endpoints within and perhaps outside of the network zone (admission), and the status of endpoints
(e.g., are they still “alive” or participating?).
H.245 is the conference control protocol. It pertains to negotiation between endpoints to establish a compatible
set of media capabilities.
Because many user-settable parameters of the MultiTech Gatekeeper software refer directly or indirectly to the
H.225 protocol, we present a summary of common H.225 messages below.
Summary of
H.323 RAS* Messages (Registration, Admission, & Status)
of the H.225 Call Signaling Protocol
In a Gatekeeper-controlled H.323 network, when call is made, the RAS channel
between Gatekeeper and endpoint is the first logical channel opened.
Admission Control
Messages
With an ARQ, an endpoint asks to participate in a phone
call. The Gatekeeper can either grant the request (by
sending an ACF message) or deny the request
(by sending an ARJ message). When admission is granted,
the endpoints participating in the call can exchange (H.225)
call signaling messages directly between themselves.
When the call is done, each endpoint, in turn, requests
disengagement (DRQ) and is granted disengagement (DCF)
by the Gatekeeper.
ARQ
Admission Request.
ACF
Admission Confirmation.
ARJ
Admission Rejection.
DRQ
Disengagement Request.
DCF
Disengagement Confirmation.
Bandwidth Control
Messages
With a BRQ, an endpoint requests a certain amount of digital
bandwidth for a call.
If the Gatekeeper grants the request,
it returns a BCF message.
If the Gatekeeper denies the request,
it returns a BRJ message, typically because all allocated data
channels are in use.
If a bandwidth request is rejected, it is possible for a call to be
conducted
* RAS in H.323 has nothing to do with the Remote Access Service that is used in
ordinary TCP/IP networks.
Summary of Contents for MultiVOIP MVP100GK Gatekeeper
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