3G中的编解码协商技术

由于在接入网和核心网传送的码流格式不一致，造成话音信号进行两次编码和解码，导致语音质量降低。因此必须采用编解码协商技术来统一全程的编解码。编解码协商技术主要有无码型变换器操作（TrFO）、无二次编解码操作（TFO）和审计网络质量优选编解码技术。TrFO是呼叫建立过程中优选的一种机制，它尝试去建立用户设备（UE）到UE的无需使用码形变换器（TC）的连接，如果成功，能够最有效地使用带觅；TFO作为TrFO的备用技术，是一种带内的编解码协商协议，因为用户面码流不再需要通过语音编解码器的压缩、解压缩处理，可以改善话音质量；审计网络质量优选编解码技术依据呼叫的接入数来灵活地选择采用G．711或G．729来编解码，作到既不过分加重网络的负担，同时又可以接入新的呼叫。

Negotiation Technologies for Encoding and Decoding in 3G System

The different formats of codec stream transported in the radio access network and the core network makes tandem operation necessary,which results in poor quality of voice. Accordingly,negotiation technology for encoding and decoding is necessary for unifying encoding and decoding in the whole process. Transcoder Free Operation (TrFO),Tandem Free Operation (TFO),and network-quantity deciding technology are leading negotiation technologies for encoding and decoding. TrFO is a mechanism for optimum selection during the establishment of a call. It tries to establish connection between User Equipment (UE) without Transcoder (TC). Its successful fulfillment enables the efficiency of bandwidth. TFO,a standby technology for TrFO,is an in-band negotiation technology for encoding and decoding. With it,the user codec stream is free from the compression and decompression by the voice codec,and the quality of voice can accordingly be improved. The network-quantity deciding technology adopts G.711 or G.729 flexibly according to the number of accessed calls. This allows access of new calls while won't increase the load of network too much.