Friday, January 16, 2009

SIP and NAT Finally? So much for SIP over 3G to Trixbox and Asterisk - OK with IAX though.

With my unlocked new iPhone 3G, I have to tell you, it's been great using SIPHON around the office. The iPhone work like a cordless VOIP phone for me now in wifi mode at the office. There are still some bugs with the auto registration, so you have to call the extension first before people can call you back which is really annoying. That being said, I also tried out SIAX (using IAX protocol instead of SIP). 

So last week, I had actually tested SIAX, but the quality and the software was flaky. However I was able to make VOIP calls through my PBX but there is definitely a lot of work on this piece of software before people actually pay for it. I would have bought it for sure since you can make VOIP calls over 3G but it was just too flaky. 

So I figured this week, I would tackle one of the tasks that I had never bothered getting around to last week, which is doing the dread SIP to SIP calls behind NATed firewalls. It was a good test anyway since I really want to be able to put SIP based handsets at remote locations without necessarily setting up a Cisco VPN Tunnel all the time because of the added overhead and cost of equipment. So after reviewing a few sites, I was able to finally get SIP to work over NAT without install SER (Sip Express Router) which is a SIP proxy server. So the good news is that over any WiFi network, I am able to connect to my Asterisk / Trixbox and make phone calls of the iPhone.  Sadly though I think Rogers somehow blocks RTP over the 3G network. I was able to establish a connection to my PBX and Call back and forth but no can do with the Audio. This thread probably explains it all.

These were the 2 Sites I used.

For Configuring Trixbox -

For Configuring Your Cisco Routers - I had no idea that the IOS was so flaky when configuring access lists, you can't do port ranges and have to do fancy work arounds:

I still need to test this with something like a Polycom Set, the iPhone seems to not like the SIP -> NAT -> NAT -> iPhone incoming and after about 60 seconds, the registration disappears (using SIPHON). So I need to confirm if this is a NAT problem or iPhone problem. I am guessing it's probably NAT, but the SIPHON software is still buggy so more on that later.

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