Voice Over IP

johnw's picture

Some notes from the mailing list about VoIP, need tidying up and extending:

On 13 Nov 2005, Paul S wrote:

Does anybody here have any experience of SIP VoIP telephony please? I'm in work and have a challenge:

 *I'm behind a corporate firewall 
 *The only way out is via the HTTP or FTP proxy 
 *Chances of getting an SIP proxy installed are very low 
 *Skype does work here but their Linux support is pretty poor 

In a perfect world I'd like to:

 *install some form of gateway at home that will let me access my home phonelines. 
 *be able to make and answer calls (preferably with caller ID) on those lines. 
 *be able to join a commercial SIP service (either direct or via my home gateway.) 
 *have a hardware SIP phone like a Cisco I can take to the office and put on my desk. 
 *be able to use the travel phone(s) on standard broadband as well as at the office. 
 *have voicemail and be able to transfer calls between the home and travel phones. 

I'm not sure if HTTP or HTTPS tunneling is possible through our HTTP proxy. It would be really great if somebody would devise a test and help me find out.

If there is a non-SIP (e.g. Cisco proprietary) system that would do the job with the home phone lines (preferably with soem bolt-on that would let me access commercial SIP) then that would be acceptable as long as the price wasn't too painful.

What do you think? Can it be done?

Nicholas B replied:

If you are behind a restrictive corporate firewall you might as well forget SIP - it needs a number of ports - 5060, and a range from 10000 upwards at the very least. Your best bet might be to set up an asterisk box at home (or wherever) and then experiment with using the IAX (an Asterisk native protocol) to contact soft phones - there a few available, including Linux, Win and Mac. As usual, though, there are more options to setting up what you want than you can shake a stick at! You may have luck tunnelling this as, effectively, an extension from the private network, as IAX normally uses only one port 4569 for everything.

As far as Asterisk goes, Asterisk@Home ( http://asteriskathome.sourceforge.net ) is a great way to start. If you have an old PC you can dedicate use the CD Distro itself - IT WILL PARTITION AND FORMAT the hard disk - so take some care!!!!!!!! This builds a Centos based Linux server, and adds A@H. Otherwise you can get a tgz file with it all in and load the tgz into a reasonable fedora or other RH derived distro. It's not really dependent on the RH style, and there are plenty of Debians etc out there, as well as OSX. Whatever, even with A@H you'll need to get under the hood and fix and configure by hand sometimes. Helpful documentation from http://www.voip-info.org - look for the Asterisk and A@H sections. The forum at http://www.voxilla.com is a handy source as well.

Sipgate are "OK" as a service provider. http://www.sipgate.co.uk, and have the advantage of very low cost when starting. Even lower cost is http://www.voipuser.org, where you can even make free outward calls to some PSTN numbers (and a good forum as well). It's very much a community run affair. If it's business critical, then use neither of these - start talking to http://www.gradwell.com - very much on the ball and modestly priced even for home use. Will also support IAX well, so you may never need SIP!!!

You can do a complete Asterisk entirely without special hardware - but if you want POTS integration you have a number of options - from cheap cards on e-bay (which work reasonably well sometimes) to Sipura 3000s which are a b**** to set up but very versatile. PC hardware anything up from an EPIA 800 mini-itx up (needs special treatment when compiling, though) will do for small installations.

Finally, test, test, test, test and test - and if you have a swmbo, test, test, test even more. VOIP is relatively immature., compared with the services from POTS companies and will quickly test the patience of users who expect 100% service levels.