本文首先介绍了IP电话的定义、业务类型、结构以及语音通信协议ITU - T的H。323系列和IETF的会话初始化协议(SIP)。

This paper firstly introduces the definition, operation type, instruction and voice communication protocol including H. 323 of ITU-T and Session Initiation protocol (SIP) of IETF.

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会话初始化协议(SIP)是IETF提出的IP电话呼叫信令协议，是一个基于文本的协议，用来创建、修改和终止多媒体呼叫与会话。

SIP is proposed by IETF as IP phone call order protocol which is totally a text modality that to be used to establish, modify and terminate multimedia calls and conversation.

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会话初始化协议（SIP）是近年来的研究热点。

SIP is one of the hot research topics in recent years.

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如何将会话初始化协议(SIP)与现有的通信网络有机结合，提供安全可靠的数据及通信服务已成为当今的热点问题。

How to combine Session Initiation Protocol (SIP) with current communication system well so as to provide secure telecommunication services has become a hot current issue.

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如何将会话初始化协议(SIP)与现有的通信网络有机结合，提供安全可靠的数据及通信服务已成为当今的热点问题。

How to combine Session Initiation Protocol (SIP) with current communication system well so as to provide secure telecommunication services has become a hot current issue.

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