在传输控制模块中，我们应用rtsp来初始化传输，用RTP来传输音视频数据，用TFRC协议来避免拥塞发生。
In transmission control module, we make use of RTSP to initialize transmission, RTP to transmit data, TFRC to avoid congestion.
延时：初始化一个对数据的请求到数据真正开始传输的时间。
Latency: the time between initiating a request for data and the beginning of the actual data transfer.
文件传输按如下顺序执行：服务器调用PrepareSendFile(. .)函数初始化文件传输。
The file transfer is made in this order: the sever initializes the file transfer by calling the PrepareSendFile (..) function.
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