D&C GLug - Home Page

[ Date Index ] [ Thread Index ] [ <= Previous by date / thread ] [ Next by date / thread => ]

Re: [LUG] OT - SIP providers?

 

On Wed, 7 Oct 2009, James Fidell wrote:

Rob Beard wrote:
Gordon Henderson wrote:

You can do direct SIP to SIP calls without using the PSTN - but like
Skype, the other end needs something compatible. (And NAT is going to
stop it working anyway)

So I guess if you have ADSL then you'd need a router which could do
bridging or something along those lines so the Asterisk box is
potentially getting the internet IP address?

Or an ISP that will provide you with a routed netblock over your ADSL
line, allowing you to have a router on the ADSL line and behind it a
DMZ for your asterisk box (and perhaps other stuff too) and a firewall
doing NAT and protecting the main office network.

That's ideal - as long as the phones are in the DMZ too. Some routers can run a parallel private network over the public one too, so you avoid using up public IPs for phones, or you put the phones behind the office firewall and use some sort of NAT traversal or STUN for the phones - which is the way it works in Drogon Towers - PBX is public (bell.drogon.net), phones are behind NAT and use STUN. The phones are not allowed to re-invite to external SIP sources, but the PBX is, so the audio data goes via the PBX.

Sadly, this isn't always possible to setup on an existing customers site, so 99% of the time you end up with the phones and the PBX being behind the NAT router. It's not hard to make it work though with port-forwarding and the right runes in the PBX... It's one reason my next revieion of PBX will act as a router - then it can have the real external IP address directly on it... That's not a solution for everyone, but it would satisfy the needs of the average SME who seems to take my kit.

However, don't try to call me by SIP dialling gordon@xxxxxxxxxxxxxxx - it simply won't work (Tom take note!) and the reason why it won't work is that I do not want to accept calls from un-authenticated sources. This is one reason e-num isn't taking off for now - I'm too afraid that spammers will start calling me!!!

Gordon

--
The Mailing List for the Devon & Cornwall LUG
http://mailman.dclug.org.uk/listinfo/list
FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html