2.3.7 Value added by Service Providers

The TAPI DLL value-added is specific to telephony, but independent of the low-level details of specific telephony devices. In contrast, Service Providers support the low-level device-specific aspects of telephony. This includes functions such as managing the states of calls, dialing, signal generation and detection, switchboard controlling, etc. The implementations of such functions differs greatly from one device to another. For example, a Service Provider providing direct management of analog phone lines would contain and control hardware for detecting on/off hook signals, generating and filtering tones, etc. A Service Provider that worked in conjunction with a PBX would send command streams over a digital network to request similar operations from a piece of remote hardware. Service Providers hide the device-specific details of how telephony operations are implemented.

To summarize: Service Providers provide the low-level device-specific mechanisms. The TAPI DLL provides the medium-level traffic management that interconnects these mechanisms with applications. Applications in turn provide the policy of how these traffic streams and device-specific operations are used to accomplish the functions desired by the user.