Windows Telephony Overview

Network Independence

For an ISV to be able to cover enough of a market to make a difference, all of the telephone network communication protocols had to be covered with a single API: POTS, PBX, ISDN, key systems, wireless, cellular and even the LAN (Local Area Network). TAPI provides a super-set API to functionality provided for all of these networks, abstracted in a way that isn't tied to a specific one. Telephony devices provide access to the various features of their networks without requiring the application to have specific knowledge related to each one.

Unfortunately, because TAPI has be a super-set of the functionality of every kind of telephone network, the API is rather large. All telephony devices can't support all of the functionality accessible via TAPI. Applications need to be aware of this and write applications that provide sub-sets of functionality based on the capabilities of the system's telephony devices. The good news is that TAPI allows an application to get a complete description of telephony device capabilities at runtime.

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