On 01/14/2012 12:36 AM, Chris Tilt wrote:
> Hello.
> Please forgive my ignorance on the subject of SIP, but I am looking
> for a solution to the SIP + NAT problem with a slightly twisted use
> case that involves establishing connections based not on phone
> numbers, but rather on unique ids of computer hosts. I am an
> experienced Erlang programmer, which is what drew me to Yxa in the
> first place, so making the extensions myself should not be a problem.
> However, I would like your opinion on the feasibility before I start
> work.
> I'd like to use UDIDs or a hash of them in place of phone numbers
> because these computers do not have phone numbers. Next, in order to
> short-circuit the not-so-rare case that the two computers are behind
> the same firewall, I'd like to include the local/private IP addresses
> in the INVITE message so that the invitee can notice a peer on an
> internal network and avoid routing packets through the firewall
> needlessly. Perhaps this is better done once the "call" is established
> via a secondary protocol message, but it seems like adding headers is
> straight forward in SIP. Am I crazy to think this?
If you want to set up a direct connection between the peers I think you
should use SDP as usual in SIP INVITEs.

> The application is remote login from a client to a host where both
> systems sit behind firewalls and know only some agreed-upon public
> name such as u...@well-known-domain.net. The incoming proxy and SIP
> router are good candidates for connection establishment through the
> NATs, with public domain at incomingproxy.well-known-domain.net. One
> more question... I noticed that STUN was added to Yxa. Do the STUN
> packets and SIP packets come out through the same port of the NAT
> (with respect to the internal side of the NAT)? If so, then it seems
> this would be a good thing to assist with NAT traversal. If not, then
> how do SIP routed messages pass into the NAT of the invitee (from
> internet side to private network side) since there would not be an
> open port? Or does this require opening of the SIP port (5060?) on the
> NAT/firewall of the peer networks?

The NATed peers will need to keep the hair pin opened in the NAT router
by regularly sending traffic to the Yxa proxy. There are several
solutions to the NAT problem. One is to put a SBC in front of the Yxa
server, another is to use ICE.


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