Patent ID: 6574469
Filing Date: 2003-06-03
Classification: G10L,H04L,H04M,H04W

Abstract:
A method of minimizing the number of transcodings of a speech signal during a conference call between a first mobile subscriber, a second subscriber, and a third subscriber, said call being transported over a packet-switched network in which Tandem Free Operation (TFO) is utilized to control transcoding of the speech signal, said method comprising the steps of:establishing a first call between the first mobile subscriber and the second subscriber using TFO; sending a message from a gateway connecting the second subscriber to the network (second gateway) to a gateway connecting the first subscriber to the network (first gateway), said message indicating a speech coding mode being utilized between the second subscriber and the second gateway; receiving an input in a Mobile Switching Center (MSC) serving the first subscriber indicating that the third subscriber should be joined in the call; establishing communications between the first gateway and a third gateway connecting the third subscriber to the network; sending a message from the third gateway to the first gateway indicating a speech coding mode being utilized between the third subscriber and the third gateway; establishing a three-way call bridge by a Conference Call Device (CCD) in the MSC serving the first subscriber, said call bridge providing a first call path to the first subscriber, a second call path to the second subscriber, and a third call path to the third subscriber, the second and third call paths going to the first gateway and using a speech coding mode supported by the CCD; encoding within the first gateway, the speech signal for the call leg to the second subscriber with the speech coding mode being utilized between the second subscriber and the second gateway; and encoding within the first gateway, the speech signal for the call leg to the third subscriber with the speech coding mode being utilized between the third subscriber and the third gateway.