TANDBERG Border Controller User Manual
Figure 2: Alternate Border Controller configuration
3.5Call Control
When an endpoint wants to call another endpoint it presents the address it wants to call to the Border Controller using a protocol knows as RAS. The Border Controller tries to resolve this address and supplies the calling endpoint with information about the called endpoint. The destination address can take several forms: IP address, H.323 ID, E.164 alias or a full H.323 URI.
When an H.323 ID or E.164 alias is used, the Border Controller looks for a match between the dialed address and the aliases registered by its endpoints. If no match is found, it may query other Gatekeepers and Border Controllers.
When dialing by H.323 URI, the destination address resembles an email address. The Border Controller first follows the procedure for matching H.323 IDs. If that fails it looks for a Gatekeeper or Border Controller responsible for the domain (the part of the URI following the @ symbol) and queries that device.
Dialing by IP address is necessary when the destination endpoint is not registered with a Gatekeeper or Border Controller. If it is registered, then one of the other addressing schemes should be used instead as they are more flexible. From your registered endpoint, dial the IP address of the endpoint you wish to call. This requires that the Border Controller has xConfiguration Gatekeeper CallToUnknownIPAddresses correctly configured.
It is not possible to dial endpoints behind a Border Controller by IP address. Calls should be made using an E.164 or H.323 alias.
Figure 3 illustrates the process the Border Controller performs when receiving call requests:
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