我们选择UDP作为承载协议，因为在低带宽的视频传输，语音传输或者其他类似应用中，UDP仍然是一种很有效的协议。
We also chose UDP because it’s an efficient protocol for low-latency streaming video conversations, voice conversations or other similar solutions.
例如，在ip电话等语音应用程序连接中，在SIP消息中使用SDP协商的协议通常是实时协议(Real - Time Protocol, RTP)，而此协议在RFC 3550中定义。
For example, in voice connections of applications such as IP telephony, the protocol negotiated with SDP in a SIP message is often Real-Time protocol (RTP), which is defined in RFC 3550.
SIP是当前IP电话的会话建立和信令控制的基础协议，SIP应用也是实现基于IP网络的语音等多种多媒体应用的基本途径。
SIP is currently the basic signaling and call setup protocol for IP telephony, and SIP applications are the basic way to provide voice and other multimedia services over IP.
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