26.2023GPPAdaptive Multi-Rate - Wideband (AMR-WB) speech codecInterface to Iu, Uu and NbRelease 17Speech codec speech processing functionsTS
The mapping of the AMR-WB Speech Codec parameters to the Iu interface specifies the frame structure of the speech data exchanged between the RNC and the TC in case of normal operation and Tandem Free Operation, respectively between RNC 1 and RNC 2 in case of Transcoder Free Operation. This mapping is independent from the radio interface in the sense that it has the same structure for both FDD and TDD modes of the UTRAN.
The mapping between the Speech Codec and the Radio Access Network within the UE is not an open interface and need not to be detailed.
The mapping on the Nb Interface is identical to the one on the Iu Interface in case of Transcoder Free Operation, with the MGW relaying the SDUs unaltered between Iu and Nb Interfaces.
In case of transcoding within the MGW the PCM coded speech is mapped onto the Nb Interface in packets of 40 octets.