Each TAPI line device enumerated by the WANTSP will not necessarily map to a physical line. Usually for an ISDN board each B channel is mapped to a TAPI line device. This means an ISDN board that has one physical line will have two line devices available to TAPI apps. Similarly, a board which has 2 physical lines would have 4 line devices enumerated by the WANTSP. It is the driver's responsibility to return a unique line device name for each line device it exposes to the WANTSP.