长连接与心跳包 Persistent connection and HearBeats
http://stackoverflow.com/questions/1480236/does-a-tcp-socket-connection-have-a-keep-alive
http://stackoverflow.com/questions/2735883/relation-between-http-keep-alive-duration-and-tcp-timeout-duration?rq=1
http://stackoverflow.com/questions/1480236/does-a-tcp-socket-connection-have-a-keep-alive
http://stackoverflow.com/questions/2735883/relation-between-http-keep-alive-duration-and-tcp-timeout-duration?rq=1
