6.2.  Handling an Incoming Call

This section discusses how the demo application handles incoming calls. It contains the following topics:

• 6.2.1.  Receiving a Call
• 6.2.2.  Handling a PSTN Call
• 6.2.3.  Handling an IP Call

6.2.1.  Receiving a Call

The demo can receive calls from either the PSTN or the IP network. The demo uses a configuration file (gateway_r4.cfg) to determine parameters that are associated with a particular call. The configuration file allows you to configure different channels with different properties. See Section 4.2.  Editing Configuration File for a more detailed description of the gateway_r4.cfg file, as well as a description of the different configuration properties.

6.2.2.  Handling a PSTN Call

A call that arrives from the PSTN needs to be routed to either a destination PSTN number (via another gateway) or to an H.323 terminal. The demo uses the gateway_r4.cfg file to determine the destination IP address as well as the (optional) destination PSTN number (remote phone number). The IP Gateway (Global Call) demo initiates an IP (H.323) call to the destination IP address. If the configuration file indicates a PSTN destination number then that number is passed to the destination gateway during the call establishment procedure.

Once the destination gateway has answered the H.323 call, the IP Gateway (Global Call) demo connects the PSTN call to the IP call. An audio path is now established between the PSTN call and the destination IP station. For more details see section 6.5.  Event Mechanism .

6.2.3.  Handling an IP Call

A call that arrives from the IP network needs to be routed to a PSTN number. That number may arrive as part of the call establishment procedure (if the call was originated by another IP Gateway for example). If the destination number arrived during call establishment, then the IP Gateway (Global Call) demo uses that number to call the PSTN. If no destination number was included in the call establishment procedure, then the IP Gateway (Global Call) demo uses the gateway_r4.cfg file to determine the destination number to call (local phone number). Once the IP Gateway (Global Call) demo answers and connects the call on the IP network, it initiates (dial out) a call on the PSTN line and connects the two calls. This allows the calling party to hear the call progress tones on the local PSTN. For more details see section 6.5.  Event Mechanism .

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