C.7 The Dialogue between TFO_BTS and TFO_BSC

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

This clause is valid for all Codec Types of the AMR-NB and AMR-WB families. If BTS and TRAU exchange Configuration information, then they shall use the meachnism defined here. From REL-5 onwards the generic configuration frames may also be used for all other codec types.

The BSC and the BTS exchange messages through Layer 3 signalling as specified in 3GPP TS 48.058 [12].

First, the BSC sends local configuration information to the BTS.

The BTS is also in contact with the TRAU and relays information received from the BSC toward the TRAU within the AMR Configuration frames (REL-4) or in generic configuration frames (REL-5 and onwards).

The BTS also extracts the configuration information sent downlink by the TRAU or the distant BTS in the AMR Configuration frames (REL-4) or in generic configuration frames (REL-5 and onwards).

Finally, the BTS relays this received configuration information back to the BSC.

C.7.1 BSC to BTS messages

The BSC at Channel activation informs the BTS of the local codec configuration. It enables or disable TFO too. It can also delegate the ACS modification to the BTS (MultiRate Control by RATSCCH).

The BSC can enable or disable TFO at any moment during a call whether TFO is ongoing or not (TFO MODIFICATION REQUEST).

The BSC informs the BTS of any change of the local configuration, if the Codec Type Mismatch resolution and/or AMR optimization is supported (MultiRate Codec Mode Req).

The BSC should notify to the BTS when an handover procedure is about to be launched (PRE-HANDOVer NOTIFication). It should also notify the BTS is the handover procedure has failed (PRE-HANDOVer NOTIFication).

C.7.2 BTS to BSC messages

The BTS should report to the BSC the status of the TFO, i.e. when TFO starts and stops (TFO REPort).

The BTS should report the Round trip delay it has estimated (Round Trip Delay REPort). It should report it every time a significant change (e.g. 60 ms) is detected in the round trip delay (see clause 8.2.4).

The BTS should report to the BSC the distant codec configuration (REMOTE CODEC CONFiguration REPort). It should also report any modification of this configuration. It should report the optimal TFO configuration, if the Optimal or Distant Configuration (OD) tells so (MultiRate Codec Mode Req).