1.4.2. Requesting Permission to Call

After registering with the gatekeeper, endpoint A must request permission from the gatekeeper to initiate the call. To do this, endpoint A sends an Admission Request (ARQ) message to the gatekeeper. This message includes information such as:

• A sequence number
• A gatekeeper assigned identifier
• The type of call, in this example, point-to-point
• The call model to use, either direct or gatekeeper-routed
• The destination address, in this case, the phone number of endpoint B
• An estimation of the amount of bandwidth required. This parameter can be adjusted later by a Bandwidth Request (BRQ) message to the gatekeeper.

If the gatekeeper allows the call to proceed, it sends an Admission Confirm (ACF) message to endpoint A. The ACF message includes the following information:

• The call model used
• The transport address and port to use for call signaling (in this example, the IP address of the gateway)
• The allowed bandwidth

All setup has now been completed and the next phase of the scenario, Call Signaling, can begin.

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