This section explains how signaling takes place when the SBC functions as a B2BGW for H.323. The following diagram illustrates the SBC acting as a B2BGW.

When configured as a B2BGW, the SBC appears as multiple H.323 gateways to multiple networks. You can think of the SBC 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 SBC 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 SBC sends ARQs to the corresponding gatekeeper in its zone when a call is received on the associated interface. In this behavior, the SBC 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 SBC to run like a gateway without a gatekeeper by turning off automatic discovery (auto-gk-discovery) for the remote gatekeeper. When the SBC receives a Setup message, it does not send an ARQ and there is no registration for admission requests. Without automatic gateway discovery, the SBC 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 SBC finds a gatekeeper.

This section explains how signaling takes place when the SBC functions as a back-to-back gatekeeper proxy and gateway for H.323. The following diagram illustrates theSBC acting as a B2B gatekeeper proxy and gateway.

In this application, with the service mode (isgateway) parameter set to disabled, the SBC responds to LRQs and issues LCFs and LRJs. It sends LRQs and LCFs/LRJs to the local IPv4 address for the H.323 interface. The SBC responds to the LRQs by providing a signaling address that performs gateway functions.

When you use it as a back-to-back gatekeeper proxy and gateway, the SBC does not issue ARQs. In addition, all parameters related to registration, such as gateway prefix numbers, are ignored.

When you do not configure a gatekeeper, the SBC uses the local policy to find the appropriate destination for the call. If there is a matching local policy, the SBC returns an LCF to the originating gateway. If no local policy matches, the SBC rejects the call by sending an LRJ.

This section explains how signaling takes place when the SBC functions as an interworking gatekeeper-gateway for H.323. The following diagram shows the SBC acting as an interworking gatekeeper-gateway.