http
http ajax
http polling ajax
http long-polling ajax
html5 server sent events
html5 websocket
comet
reference:
0. http://stackoverflow.com/questions/11077857/what-are-long-polling-websockets-server-sent-events-sse-and-comet/12855533#12855533
1. websocket 实现对比: http://einaros.github.io/ws/clients/index.html
2.