| In the current trend of all IP based network evolution,core network and wireless access network have began to achieve IP-based.After the A-interface IP-based,it has the ability to carry compressed codec,so it is possible to carry the same codec from end to end to avoid codec transforming,saving devices and improving voice quality.In the available codec negotiation techniques,only the TrFO requires no transcoders.But,after the core network IP-based,the number of codec increased,and the choice of codec was more flexible.As equipment manufacturers' policies for codec choosing are not compatible,and the configuration of network nodes for codec negotiation process are not compatible,so TrFO is difficult to achieve.The failure of codec negotiation will result in the failure of call establishment.For the above problems,the network has not used TrFO technology,core network side is still required Transcoders.Therefore,in the A-interface over IP environment,achieving TrFO to save devices,and to enhance the speech quality is urgent.International standard only defined the TrFO for 3G network,TrFO has never been used in AoIP 2G network.To achieve TrFO,there still needs to consider many factors,such as:AMR rate set configuration is not unified,and which is difficult to negotiate;Assignment process and the codec negotiation process are not compatible,so there still unable to achieve TrFO.This paper proposed the solution for end to end speech codec negotiation.According to the calling,handover and other processes,designed a specific codec negotiation policy,and modified the codec configurations of the network nodes and interfaces to achieve this solution.The testing in laboratory and current network environment has verified the feasibility and implementation effect of this solution.The results show that TrFO can be successfully achieved in various scenes in the network after using this solution,and the transcoders were saved,voice quality is enhanced obviously. |
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