Client/Server Telephony

In a client/server environment, TAPI provides distributed access to shared telephony resources. For example, a LAN-based server might have multiple telephone-line connections to a local telephone switch or PBX. TAPI operations invoked at any associated client are forwarded over the LAN to the server. The server uses third-party call control between the server and the PBX to implement the client's call-control requests.

This model offers a lower cost per computer for call control if the LAN is already in use.

The server can be connected to the switch using a switch-to-host link. It is also possible for a PBX to be directly connected to the LAN on which the server and associated clients reside. Within these distributed configurations, different subconfigurations are possible:

• To provide personal telephony to each desktop, the service provider could model the PBX line associated with the computer (on a desktop) as a single line device with one channel. Each client computer would have one line device available.
• Each third-party station can be modeled as a separate line device to allow applications to control calls on other stations. (In a PBX, a station is anything to which a wire leads from the PBX.) This enables the application to control calls on other stations. This solution requires that the application open each line it wants to manipulate or monitor.
• The set of all third-party stations can be modeled as a single line device with one address (one phone number) assigned to it per station. Only a single device is to be opened, providing monitoring and control of all addresses (all stations) on the line.

A major advantage of such client/server implementations is a lowered cost of telephony services per client application.

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