Service Levels

The Telephony Service Provider Interface defines three levels of service:

• Basic Telephony The lowest level of service, which provides a guaranteed set of functions that are equivalent to POTS functions (make and receive calls). All service providers must support Basic Telephony functions.
• Supplementary Telephony Provides advanced switch features such as hold, transfer, and so on. All Supplementary services are optional; that is, the service provider is not required to support them.
• Extended Telephony Provides well-defined API extension mechanisms that enable application developers to access service-provider specific functions not directly defined by the Telephony API.

The set of TAPI functions do not map one to one onto the set of TSPI functions. In particular, functions related to privilege, phone number translation, and interapplication communication are handled by TAPI and have no corresponding function in TSPI. Other functions, such as those used for service-provider configuration and initialization, have no corresponding functions in TAPI.