Telephone interexchange signaling protocol

Abstract

Disclosed are schemes for selecting an interexchange telephone call carrier, selecting a route to the selected carrier, and establishing a call path on the selected route to the selected carrier in a multicarrier environment. Call path establishment from an end office at which a call is originating to the carrier's office is accomplished via a multifrequency signaling scheme. If the call is an international call or the route is an indirect route to a carrier via an access tandem, following seizure of a trunk the end office outpulses thereon a first sequence of information that characterizes the subsequent route that the call should take, including identity of the interexchange or international carrier. After receiving a wink responsive to the first sequence, the end office outpulses a second sequence. If the call is a domestic call routed directly to a carrier, following seizure of the trunk the end office begins outpulsing with the second sequence. The second sequence generally contains information characterizing the source of the call, such as information on the class of service of the calling terminal and possibly Automatic Number Identification (ANI) code. Following the second sequence, the end office outpulses a third sequence of information characterizing the destination of the call, i.e., the called number, if such information is available. The end office then awaits receipt of an acknowledgment wink indicative of receipt by the interchange carrier of the second and selectively the third sequences. Upon receiving the acknowledgment wink, the end office cuts-through the call path to the trunk.