3GPP在R5版本中首次提出了IP多媒体子系统(IMS)的概念,SIP协议被选择为呼叫会话控制协议.由于SIP是基于文本的协议,在会话过程中需要重传大量的数据,导致在会话建立过程中时延的增加.文中在分析现有的SIP信令压缩算法的基础上,提出了一种带有预处理的LZSS与算术编码相结合的改进算法.首先对消息进行预编码,然后进行LZSS压缩,压缩完后与算术编码相结合,这种改进后的算法减少了信令传输延迟.文中运用典型的SIP会话环境进行仿真实验,其结果验证了改进算法能够有效地提高性能,缩短消息长度和减小传输时延.%IMS was introduced into R5 core network by 3GPP. SIP was chosen as the call session control protocol. SIP is text-based and has a lot of retransmitted data, which causes more delay during the process of the create session. It proposes an improved compression algorithm which includes LZSS and arithmetic coding with pretreatment on basis of the existing compression algorithm of SIP. Firstly, the message is coded with pretreatment. Then, the message is compressed by LZSS. Finally, the message is combined with arithmetic coding. The simulation experiments are made based on typical SIP session scene. The results of experiment confirm that the improved algorithm can improve performance, shorten message size and reduce transmission delay.
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