4.4 Document Content

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

In the following, clause 5 defines the structure of the TFO Frames exchanged between the Transcoder Units. The TFO Frames carry the compressed speech (payload) and some control bits for the inter-transcoder in-band signalling. Clause 6 introduces the elementary procedures used for the establishment and maintenance of Tandem Free Operation. Clause 7 defines the detailed content of the TFO messages associated with the TFO procedures. The TFO Message Structure follows the generic format defined in Annex A. Clause 8 defines how the TFO messages are mapped onto the TFO Frames. Clause 9 defines the TFO State Machine. Clause 10 contains the detailed TFO protocol. Clause 11 and 12 specify the TFO Decision algorithm and the optional Codec Mismatch Resolution.

Annex B is an informative annex defining the expected behaviour of In-Path Equipment (IPE) for compatibility with Tandem Free Operation.

Annex C and Annex D define specific TFO processes for GSM and 3G systems.

Annex E contains a reference implementation for the TFO decision algorithm (C-code) described in clause 11 and 12.

Annex F is an informative Implementer’s Guide containing recommendations in the implementation and introduction of AMR TFO.

Annex G provides basic Message Flow sequences for the TFO protocol.