6.12 Incoming data call from PSTN

23.1533GPPOut of band transcoder controlRelease 17Stage 2TS

For incoming calls from PSTN, the TMR may not allow to identify the requested service, since the same value may be used to identify both voice and data calls.

6.12.1 Identification of data call at Visited MSC

An incoming data call from the PSTN may be identified as data call using signalling interaction with the terminating UE at the Visited MSC. The following procdures are recommended in a network supporting TrFO to allow the Visited MSC to identify the data call using interactions with the terminating UE:

The GMSC includes a G.711(and possibly other codecs) in the BICC supported codec list.

If the Visited MSC determines that an incoming call is a data call, it shall select G.711 as codec.

Note: A 64 kbit/s bearer, as required for data calls, will be set up if G.711 is selected.

Figure 6.12.1/1.Identification of incoming data call at Visited MSC

6.12.2 Handling at transit exchange in inhomogenous networks

If a transit exchange connecting a packet backbone and a TDM backbone in an inhomogenous network is not able to determine if an incoming call from the packet backbone side is a data call or a speech call (e.g. TMR=3.1kHz is received), it may select G.711 as codec to enable possible data calls.

Note: A 64 kbit/s bearer, as required for data calls, will be set up if G.711 is selected.

Figure 6.12.2/1.Handling of possible data call at transit exchange between TDM and packet backbone

6.12.3 Identification of data call at G-MSC using multi-numbering

If the called mobile subscriber is configured with multinumbering service, the GMSC may use the GSM Bearer Capability that may be received from the HLR during the Send Routing Information procedure to identify the requested service and select directly a codec transparent for data call. It may also pass the bearer capability information to subsequent nodes to allow them to select a codec transparent for data call as well (see 3GPP TS 29.007 [19]). This may be particularly usefull in configurations where the terminating MSC does not participate to the codec negotiation procedure, as illustrated in figures 6.12/1 and 6.12/2.

Figure 6.12.3/1.Use of the GSM Bearer Capability by TDM GMSC for incoming data call from PSTN

Figure 6.12.3/2.Use of the GSM Bearer Capability by GMSC for incoming data call from PSTN