Introduction of transcoder free operation into core network

This paper provides technical discussion regarding the introduction of transcoder free operation (TrFO) into 2G and 3G core networks. In particular, it focuses on the opportunities for transmission savings balanced with the effect of speech quality, when using different speech compression and out-of-band transcoder control (OoBTC) for GSM, WCDMA (wideband code division multiple access) and external network accesses. Implementation is required according to 3GPP (3rd generation partnership project) standards. OoBTC and TrFO are part of 3GPP release 4. OoBTC is a mechanism to negotiate the codecs and codec modes on a call-by-call basis, using out-of-band signalling. Mechanisms for codec negotiation at call set up, and codec modification after call set up, are provided by the standard. OoBTC and TrFO are applicable only to ATM (asynchronous transfer mode) and IP (internet protocol) based core network, using BICC (bearer independent call control) call control protocol.