IAX2协议简介

IAX2协议与SIP协议一样, 属于VOIP协议;

1 .是一个私有的协议（SIP是IETF定义的标准化协议）.   

2. 使用1个UDP端口同时用于信令和音频数据的传输.  

3. 目前只用于音频传输.

4. 不提供p2p服务, 所有数据均通过server转发.

至于网上说的, 

Signaling and data travel togheter in IAX avoiding the problems of NAT that usually appear in SIP. Signaling and data in SIP travel using different protocols and that is why NAT problems appears. Audio stream have to pass through routers and firewalls. SIP usually needs a STUN server to avoid these problems.

这句话很容易让人误解,  我一直理解为IAX不需要NAT穿越, 能够直接P2P(这不现实, 它不可能只凭一个中转server就能打通所有类型的p2p. ); 实际上是:

- Audio flow when using a server

If SIP is using a server signaling messages always pass through the server but audio messages (RTP flow) can travel end to end without passing through the server. In IAX, signaling and data must pass always through IAX server. This increases the bandwidth need by the IAX servers when there are many simultaneous calls.

IAX 的所有数据(IAX只传输音频, 所以数据量不大) 均通过server中转, 根本没有p2p. 

没有p2p连接, 为什么老提NAT，容易让人误解.

以上也是来自网络, 并没有看IAX2源码.