[asterisk-users] Understanding NAT Traversal

[Mojo with Horan & Company, LLC]

H,

hugolivude wrote:
>> For various reasons, I'm not too partial to UPnP, but maybe there needs
>> to be a SIP UA that uses UPnP to configure a NAT router for it, when an
>> RTP stream is begun?
> 
> Not following this part...
While I could probably never bring myself to enjoy (Microsoft's?) 
Universal Plug-n-Play features, they would be helpful for the rtp 
streams, although not the signalling.

Conceivably, if only one SIP UA were in use behind a NAT router, then 
when it constructed a call and needed to receive RTP streams, it would 
configure port mappings in the router via the UPnP protocol, so external 
port 10xxx is forwarded to the internal IP of the SIP UA.  It could 
remove this port mapping when the call was deconstructed.

The problem of course happens when two SIP UAs need to work behind a NAT 
router, because, as Cullin mentioned, "It is very difficult to track
a a many-to-one NAT (technically port address translation (PAT)) when 
you can't change the source or destination ports. "

Thanks Cullin!

Moj