Matt Mossholder on 13 May 2011 18:37:02 -0700

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Re: [PLUG] Future of Skype on Linux?

On Fri, May 13, 2011 at 5:58 PM, Edmond Rodriguez <> wrote:
There are various techniques that are used, right pluggers? ÂA Stun
(or is it STUN) server comes to mind, though Skype may have their own
way of doing things. Â In some cases it is not always successful, but
often is. Â When not, a relay is needed, but often a P2P connection
can be accomplished. ÂIt just has to be negotiated via a middle
server, which then can get out of the way. Â Any big network people
out there to embellish? Â

I am answering cautiously, so someone else, do please jump in and
acknowledge, Âadd, or correct what I am saying.

STUN is used for outbound NAT traversal, so that the node can determine what IP is valid on the internet side of things. If you want people to be able to make SIP calls to you, without having a registrar (true peer-to-peer), then you have to start forwarding ports in from your firewall, or have a SIP proxy on your gateway. Additionally, typically STUN only works for one system behind the firewall at a time.Â

If you are using a registrar (a SIP service provider, so to speak), then your node will periodically update the registration with the registrar, with usually is enough to keep UDP NAT working for inbound calls to one node.

If you have multiple systems that need to use SIP, you pretty much need a proxy for inbound calls, although you can typically make outbound calls.

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