TAPI provides a number of functions for manipulating call handles, determining the relationship among lines, calls, and address, and so on. Most of this functionality is implemented strictly within tapi32.dll without reference to the service provider, except for TSPI_lineGetCallAddressID. This function retrieves the address identifier of an existing call within its line. Service providers that model a line as a group of address identifiers can choose an unpredictable address for a new inbound or outbound call. This function gives tapi32.dll sufficient information to implement the lineGetNewCalls operation when it is invoked with the LINECALLSELECT_ADDRESS option.