http://www.binarytides.com/linux-ss-command/　　

https://tools.ietf.org/html/rfc2068#section-8

https://tools.ietf.org/html/rfc7230#section-6.3

https://en.wikipedia.org/wiki/HTTP_persistent_connection

http://stackoverflow.com/questions/410616/increasing-the-maximum-number-of-tcp-ip-connections-in-linux

TCP连接复用（TCP Connection Reuse）                          

http://blog.csdn.net/chdhust/article/details/12171263

使用netlink的NETLINK_INET_DIAG协议获取所有套接字信息出错 

http://bbs.chinaunix.net/thread-3766684-1-1.html

connections