A.0 Scope of Annex A and Annex B

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

Inband Signalling Messages (IS Messages) can be used to construct a specific IS Protocol for the communication between telecommunication entities for various purposes. The original purpose was to establish Tandem Free Operation of Mobile-to-Mobile calls in GSM networks. The IS Messages provide communication channels inside the speech signal paths between the speech transcoders.

In addition IS Messages allow the control of equipment within the speech signal paths between these telecommunication entities (e.g. speech transcoders). These equipments are termed "In Path Equipments" (IPEs).

Annex A defines the generic structure of these IS Messages and rules for the IS_Sender.

Annex B defines the generic rules with respect to these IS Messages for the IPEs.

Annex A is mandatory for TFO–capable Transcoder Equipment and informative for IPEs.

Annex B is informative for TFO–capable Transcoder Equipment.

Annex B shall be followed by IPEs, which want to be compatible to IS Messages.