23.0533GPPRelease 17Service descriptionStage 2Tandem Free Operation (TFO)TS
In-band TFO aims to remove the speech coding and decoding done in the BSS in MS-to-MS calls in order to improve the perceived speech quality. In-band TFO is established after call set-up using in-band signalling. This signalling is therefore controlled by the TRAU.
Using in-band signalling implies that the link between the TRAUs is transparent in the sense that the digital content of what is emitted by a TRAU is not modified. The so-called In Path Equipments must therefore be disabled or configured in such a way that the information (signalling and coded speech) required for Tandem Free is not altered.