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I've been playing with VoIP IP PBX solutions for a few months, but I'm trying to find a solution that will allow for the following:

  • An IP PBX based in a data centre (where SIP trunks will terminate), idea being that the company has a single number for everything.
  • Several(~10) IP phones in several offices (4).
  • Each office has a standard SOHO router rendering most SIP-based IP handsets useless because of NAT.
  • Each user needs an extension that they can take with them (soft-phones) or log into a phone with ("hotdesking").

IPSec VPN linking the office to the PBX is not an option here.

Any advice greatly appreciated.

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3 Answers

What about any kind of VPN? I've done VOIP over OpenVPN before; it works fine - run it on something behind the SOHO router and map the openVPN port to the openVPN server. You can then run any number of SIP phones over this virtual link with no security risk.

Or you could portmap router ports on the SOHO routers to the SIP port on the handsets, though I'm not up on the state of VOIP encryption, which may be an issue for you.

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can you elaborate on your first point? would multiple handsets be able to use the same openvpn connection? I've avoided directly mapping the handsets because afaik SIP is a plain text protocol, not sure RTP would play nicely with that either –  BoyMars Oct 1 '10 at 10:30
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up vote 0 down vote accepted

I'd actually forgotten about this, I'm thinking of investigating Microsoft's Lync Server since it's new enterprise voice features cover a lot of what i'm looking for.

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yep it'll do all that, we do it now with OCS 2007 R2 in a colo away from HQ and moving to Lync –  Bret Fisher Mar 9 '11 at 3:24
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Ah? Crap?

I would except any SOHO router to work perfectly with a SIP client because VOIP is by now a standard protocol that a LOT of home users rely on. Look at all the public SIP services.

The whole NAT thing is actually handled perfectly in SIP with the use of a redirector.

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there's a number of SOHO routers that make use of SIP ALGs and their own voip services which interfere with SIP/RTP –  BoyMars Nov 8 '10 at 18:20
Yes, and you can turn that off normally. The inability to use an external SIP provider puts a SOHO router into crapspace. –  TomTom Nov 8 '10 at 18:43
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