Patent ID: 8391280

Claim:
A method for implementing lossless transmission of a media stream after switching from a plain-call to a cipher-call, applied in a system comprising a base station, a media gateway and a communication terminal, the method comprising the following steps of: A. after the base station receives a plain-call to cipher-call switch message for switching from a plain-call to a cipher-call from the communication terminal, inserting a special media frame indicating that the plain-call to cipher-call switch has been performed into the media stream and then sending the media stream to the media gateway; B. the media gateway determining whether to detect the special media frame or not according to incoming and outgoing media bearing modes of the media stream, or according to incoming and outgoing media bearing modes and media encoding-decoding formats; and C. the media gateway passing through the media stream from the incoming to the outgoing regardless of whether the special media frame is detected or not to be detected; wherein, in the step B, if the special media frame is detected by the media gateway, adapting code packets of the media stream to a 64 kbps/56 kbps Pulse Code Modulation (PCM) code stream and then transmitting the PCM code stream to the outgoing media stream.