5.3 Media Gateway Control for Codec Handling

23.1533GPPOut of band transcoder controlRelease 17Stage 2TS

The general handling of MGW control procedures are detailed in [8]. Specific handling related to the control of the speech encoding is detailed in Figure. 5.3/1. The terms context, termination, streams and stream properties are described in the ITU-T H.248 "Media Gateway Control Protocol" [13].

Figure 5.3/1. MGW control for speech codec

The handling of transcoding between one codec type (media stream property applied at one termination) and another codec type (media stream property at other termination) is a function of the MGW. The media stream property for Audio Codec Type is defined in Annex C of the ITU-T MGW control protocol, H.248.

If TFO-incompatible codec types are applied at different terminations of the same context, the MGW shall insert a transcoder. For the definition of TFO-compatibility between 3GPP codec types and codec configurations see [10], clauses 11 and 12.

Between codecs of the AMR type, the MGW need not insert a transcoder, if the codec types are TFO- compatible according to [10], table 11-1, and

– the codecs use the same ACS; or

– the ACSs are TFO-compatible and the use of codec modes is restricted to a common subset of the ACSs by means of maximum rate control. In this case the MGW shall coordinate the rate control request.

Between codecs of the AMR-WB type, the MGW need not insert a transcoder, if

– the codecs use the same ACS; or

– the use of codec modes is restricted to a common subset of the ACSs by means of maximum rate control. In this case the MGW shall coordinate the rate control request.

Between codecs of the EVS type, the MGW need not insert a transcoder, if

– the codecs use the same ACS; or

– the use of codec modes is restricted to a common subset of the ACSs by means of maximum rate control. In this case the MGW shall coordinate the rate control request.

Between codecs of the AMR-WB type and codecs of the EVS type, the MGW need not insert a transcoder, if

– the codecs of the EVS family are operating in AMR-WB IO mode; and

– the codecs use the same ACS or the use of codec modes is restricted to a common subset of the ACSs by means of maximum rate control. In the latter case the MGW shall coordinate the rate control request.