SIP相关

SIP呼叫流程典型流程图解及其详细解释

http://blog.csdn.net/xiangjai/article/details/8837828

【协议学习】SIP基本场景分析

http://www.cnblogs.com/gnuhpc/archive/2012/12/10/2812095.html

https://wk.baidu.com/view/63d1f9d36f1aff00bed51ece.html?ssid=0&from=2001a&uid=0&pu=usm@2,sz@1320_2003,ta@iphone_1_10.2_1_11.4&bd_page_type=1&baiduid=8F197F75035F9C518C7808FF07897326&tj=www_normal_4_0_10_title#3