6.9 Mobile to Mobile TrFO Call Establishment for GERAN Iu-mode

23.1533GPPOut of band transcoder controlRelease 17Stage 2TS

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

Figure 6.9/1: Configuration during Call Setup of a Mobile to Mobile Call for GERAN Iu-mode

The description of Figure 6.1/1 (Configuration during Call Setup of a Mobile to Mobile Call) within clause 6.1 applies for the network and protocol entities involved in the Mobile to Mobile Call for GERAN Iu-mode scenario with following modifications:

BSC-T acts as a RNC-T.

BSC-O acts as a RNC-O.

Therefore Figures 6.1/2 to 6.1/4. (the respective message flows for mobile to mobile call setup) apply as well with the appropriate modifications outlined below:

Codec negotiation

Step 1. until 6., that give the codec negotiation phase in Figure 6.1/2, shall be applied with following modifications:

Before step 1 (BSC-O to MSC-S-O) and step 4 (BSC-T to MSC-S-T) the RANAP Initial UE message will be sent indicating the GERAN capabilities, which will be available at the RAB establishment procedure. The IE describing the GERAN capabilities contains a list of codec types as well as the supported codec modes (for an adaptive multi-rate codec type), which will be available at the RAB establishment procedure. With this information the MSC Server shall puncture out (i.e. delete) those codec types and codec modes (for an adaptive multi-rate codec type) from the supported codec list taking into account the GERAN classmark and the MS capabilities which are not supported by the GERAN. This possibly reduced list shall be used by the MSC Server during the negotiation procedure (step 2 and step 6). For definition of list of supported codec types see [15].

The MSC-Server performs codec negotiation according to clause 5.6 with the following modifications:

The value of the maximum number of supported codec modes shall be set to "four" (see [10]).

RAB Assignment

RAB Assignment shall be performed as described in clause 6.1 with following modifications:

Additionally, the MSC Server shall include the selected codec type within RAB Assignment.