[Asterisk-Users] Q about IAX (and IAXy)

[Nabeel Jafferali]

This is somewhat related to my other query on the list regarding NAT
traversal.

I have heard many times that IAX is "NAT-transperant". I am unsure how
it accomplishes this.

I do know that SIP works like this: your SIP device send a request to
the SIP server (usually on port 5060) with whatever command. The SIP
server respends to your device's "apparent" IP and port (this is decided
depending on how that NAT is set up, STUN, etc.). The voice is then sent
to the "apparent" RTP port on your device (deciding what that is, again,
would depend on the NAT set up).

How does IAX eliminate this problem of ports being "mapped" by your NAT
router and external IPs? Does it use one port for both commands and
voice packets? Does the remote server just use the "received from" IP
address and port to respond?

Finally, would an IAXy work seamlessly in a configuration where it is
plugged into a NAT router which is plugged into another NAT router  -
double NATted? The * server is on a public IP.

--
Nabeel Jafferali
tel: 647.722.8457 x201
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email/msn: nabeel<at>jafferali.net