Each line has one or more channels. The channels are identical and therefore interchangeable. The service provider can pool channels for use as shared resources. The service provider can also combine two or more channels for use in a single call to provide a wider bandwidth for exchange of information. This technique is often called inverse multiplexing.
The service provider allocates one or more channels in a line in response to a request to make or answer a call. Because a line's resources have identical capabilities and are interchangeable, there is no need for TAPI to explicitly identify the channels to be used. The service provider owns and completely manages the channels of each line.