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28 series - Tandem-free operation of speech codecs

Up to the UMTS specifications 28.062 - Inband Tandem Free Operation (TFO) of speech codecs; Service description; Stage 3


In theory, the 28 series covers the Iu interface between the radio access network and the core network. In practice, most of these issues are handled by the 25 series, and the only thing left is the specification of tandem-free operation of speech codecs.

In most voice calls, the speech frames are only compressed over the radio interface, and the fixed networks contain transcoders that carry out compression and decompression. In tandem-free operation, the transcoding functions are by-passed, and the compressed speech frames travel all the way from one mobile to the other. This reduces the data rate in the fixed network, and improves the quality of the voice call.


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