1、H323,SIP等VOIP协议规范说明
http://www.protocols.com/
Protocols.com offers a comprehensive listing of data communications protocols, their functions in respect to the OSI model, the structure of the protocol and various errors and parameters.
2、H323等协议介绍
http://www.packetizer.com/ipmc/h323/standards.html
Welcome to Packetizer, a leading resource of information related to emerging information technologies, includingcloud computing, web development, and packet-switched conversational protocols (e.g.,VoIP andvideoconferencing).
3、ITU H323
http://www.itu.int/rec/T-REC-H.323/