Speech coding in a telecommunication system

摘要

An arrangement for setting up a call between first and second mobile telecommunication networks in which the speech codec to be used is negotiated between the two networks. At least one of the networks comprises a tandem free operation (TFO) device outside the radio access network and the negotiation occurs between the TFO devices of the first and second networks. The radio access network is notified of the determined speech codec by sending a call control message from the associated TFO device. The two mobile telecommunications networks may be interconnected by the PSTN. The arrangement helps prevent a degradation in speech quality by allowing the coded speech to be passed between the two networks without further coding and decoding operations.