In order to improve voice quality for mobile to mobile call (MT-MT call) in GSM Phase 2+ network, Tandem Free Operation (TFO) using in-band signalling has been specified. The equivalent function in Japan's PDC (Personal Digital Cellular) network is known as Transcoder Bypass, which has been specified to make use of out-of-band signalling control (i.e. by the PDC-MAP protocol).
Besides, there might be other advantage avoiding the transcoders. Since the voice coding rate used by mobile is relatively lower then 64kbps coding rate that is used in the fixed network, The transcoder avoiding connection could be used to reduce inter-Mobile services Switching Centre (MSC) transmission bandwidth.
These advantages should be applied not only for speech calls but also for data communications such as Facsimile, Modem, PPP/PIAFS and so on.
The purpose of the present document is to study:
The feasibility of out-of-band transcoder control in UMTS/IMT-2000 networks.
The impact of out-of-band transcoder control on the UMTS/IMT-2000 specifications.
This TR introduces one enhanced in-band transcoder control procedure and four out-of-band transcoder control procedures that might be adaptable for transcoder control in UMTS/IMT-2000 networks. Then compare each procedure from various point of views to seek the most feasible procedure.
full Table of Contents for TR 23.911 Word version: 4.0.0