8 Interactions with Other Services

23.0533GPPRelease 17Service descriptionStage 2Tandem Free Operation (TFO)TS

8.1 General

The identified interactions are with the supplementary and basic services that modify the configuration of a communication.

One example of Supplementary Service is Explicit Call Transfer, where a MS to MS communication can result in a MS to non-MS communication. Similarly, in a communication where user A is a Mobile user and User B is not a Mobile user become a communication between user A and user C where both are Mobile users.

One example of Basic Service is Alternate speech and data, where TFO should not degrade the transitions between speech and data.

More generally, the identified interactions are all related to the transitions between a configuration where TFO is possible (and potentially used) and a configuration where TFO is not possible.

The consequence of a Multiparty Call is that TFO operation is not possible.

The interactions between TFO and Lawful Intercept will depend on the capability of the devices used in such a case to not alter the in-band information (signalling and coded speech) required by the in-band TFO system. These devices can either use the 6- or 7- bit PCM available on the A-interface.

The SS that modifies the digital content of what is emitted by a TRAU will interrupt TFO. Nevertheless as soon as the transparency is re-established the TRAUs will attempt re-establishing TFO.

8.2 Support of DTMF

The existing DTMF could be applied independently of TFO. It should be noted that DTMF in TFO operation means Mobile Terminated DTMF which is currently excluded from the standard.

The DTMF when inserted by the MSC will interrupt the TFO since the TFO speech frames are modified when crossing the MSC.

The TFO must be re-established as soon as possible when the DTMF insertion stops.