https://mp.weixin.qq.com/s?__biz=MzU5NjA0OTUzNg==&mid=2247484636&idx=1&sn=520e70a8f3aa13f4e56d9703de427855&scene=19#wechat_redirect
典型案例分析：P-CSCF restoration and discovery
原文：https://www.cnblogs.com/yz123/p/13214954.html
