Back-to-Back Gateway Signaling
This section explains how signaling takes place when the Oracle® Enterprise Session Border Controller functions as a B2BGW for H.323. The following diagram illustrates the Oracle® Enterprise Session Border Controller acting as a B2BGW.
When configured as a B2BGW, the Oracle® Enterprise Session Border Controller appears as multiple H.323 gateways to multiple networks. You can think of the Oracle® Enterprise Session Border Controller as having virtual gateways, that discovers and registers with a gatekeeper in its respective domain. In this configuration, you need to set the service mode (isgateway) parameter for the H.323 interface to enabled for two H.323 interfaces. These interfaces are related either through their outgoing interface (assoc-stack) parameters or through routing policies.
If you configure your Oracle® Enterprise Session Border Controller to operate in this mode, it does not issue or respond to LRQs by either confirming them or rejecting them.
In the diagram above, the Oracle® Enterprise Session Border Controller sends ARQs to the corresponding gatekeeper in its zone when a call is received on the associated interface. In this behavior, the Oracle® Enterprise Session Border Controller acts as a gateway, complying with the H.323 standard, and registers with the configured gatekeeper in its assigned zone. You set all parameters related to the gateway registrations, such as gateway prefix numbers, in the H.323 interface configuration.
In this mode, you can also configure the Oracle® Enterprise Session Border Controller to run like a gateway without a gatekeeper by turning off automatic discovery (auto-gk-discovery) for the remote gatekeeper. When the Oracle® Enterprise Session Border Controller receives a Setup message, it does not send an ARQ and there is no registration for admission requests. Without automatic gateway discovery, the Oracle® Enterprise Session Border Controller uses the local policy to find the appropriate destination for the call. This destination is normally the IPv4 address of the endpoint or gateway, using the well-known port 1720.
If you enable this capability, then the Oracle® Enterprise Session Border Controller finds a gatekeeper.