D.4 TFO in the RNC

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

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

The RNC does not differentiate between "Normal Tandem Operation", "Transcoder Free Operation" or "Tandem Free Operation". Therefore no TFO_RNC process is necessary.

The RNC is aware that Rate_Control_Req Commands may be sent from the CN that restrict the maximally allowed rate in uplink direction. It sends Rate_Control_Ack messages back for confirmation, including the Rate Control for downlink. For details see 3GPP TS 25.415. The Rate_Control_Ack is important for the TFO_Protocol to go into the KONNECT state.

Note 0: Iu User Plane Frame Protocol (see [17]) Release ’99 cannot be used for TFO, unless there’s only one mode in the ACS, since it does not support up-link rate control.