D.6 Determination of the Optimal Codec Type and Optimal Configuration Parameters

28.0623GPPInband Tandem Free Operation (TFO) of speech codecsService descriptionStage 3TS

The determination of the Optimal Codec Type and Optimal Configuration Parameters for TFO is performed within the TC, based on the TFO Decision rules (see clauses 11 and 12). The Optimal Codec Type and Configuration is then reported to the MSC Server.

If a change of the Codec Type is not desired, then the MSC Server shall not provide more than one Codec Type within the Codec List.

If a change of the Codec Configuration is not desired, then the MSC Server shall not provide the Optimisation Mode with "Change".

But if Mismatch Resolution and Optimisation is allowed, then the MSC Server shall receive from the TC the optimal Codec Type and Optimal Configuration Parameters and the distant Codec List. The MSC Server shall accept the proposed Optimal Codec Type and its proposed optimal Configuration and perform Codec Modification. This ensures that both radio legs obtain the same result, as negotiated via the TFO protocol. If necessary TFO is disabled before and enabled after the modification.

Annex E (normative):
TFO Decision Algorithm in C-Code