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Aswath Rao On Why Trapezoidal VoIP Is Evil!

alt_vvx1500_2_1This week’s VUC call sure is timely for me! VoIP pioneer Aswath Rao will be walking us through the evil that is “trapezoidal VoIP.” His words, not mine.

Why is this extra timely for me? Well, I spent considerable time today dealing with the very trapezoid in question. My forthcoming review of the Polycom VVX-1500 Business Media Phone has gone to the publisher for a final polish. With the text in their hands my task turned to producing the supporting images, sound files, etc that they might want to run. This time around they want to run a recorded video clip example of the what you see on the VVX LCD screen. It’s a good idea, but as it happens, not so easily done.

The VVX has call recording capability compliments of the Polycom Productivity Suite, which is standard on this device. But at present it doesn’t record video…just the call audio.

So I thought that I’d contact one of the ITSPs that support the VVX-1500, thinking that I could leverage their video voicemail feature to record a clip. How hard could it be? I call them by SIP URI…they don’t answer…I leave a scripted video message. They send me the resulting clip.

It turns out the video voicemail is not really a solution. I’d have to be properly signed up as a customer, pay them, etc for the VM thing to be available. It’s worth noting that these VVX phones are really only supported by ITSPs using the BroadSoft platform, so the matter is not entirely in-house for them. They don’t know me at all & I’m asking them a favor in return for a mention in the review.

They suggest that I use Wireshark to capture the traffic, from which they can give me a video clip in a useful file format. That sounds like a plan. But to use Wireshark to capture the traffic I need either an old hub hub or a managed switch, where I could set two ports to mirror each others traffic. No got, in either case. Foiled at every turn, or so it seems.

Finally we decide that if I can place a call to them they can capture the traffic at their end and do the file conversion. Great! However, at their end there is an issue with NAT/firewall traversal. It could probably be overcome, but I can’t exactly demand that they drop everything and do this thing for me. I don’t even have any funds to pay for their time.

Finally, I decide to issue them SIP credentials on my OnSIP account. That way we both register with an out-of-house SIP registrar and all is well. We have an initial call with video, and I am a happy guy. We’ll record a short, more scripted conversation Friday afternoon and editor Tim will doubtless be happy. I am so accommodating. I never meet deadlines, but that’s another matter.

Trapezoidal VoIP is all about the apparent necessity of an out-of-house registrar in the matter of firewall and NAT traversal. It’s closely connected to matters of security and identity.

Aswath Rao is one of the early VoIP bloggers, his site having launched in December of 2003. He was also involved in the creation of what we now know as Session Border Controllers (aka SBCs.) His current project, EnThinnai is a kind of social network site that includes, amongst other things, voice chat between users without needing any intermediaries. It has a dynamically downloaded VoIP client that leverages SPEEX to deliver wideband calling without even a SIP registrar.

It should make for an interesting call. I hope that you’ll join us at at noon EDT on Friday.

Incidentally, one of the questions that kept recurring back at Pulver’s HDComms event in May was, “How do I setup my firewall to allow SIP traffic from any host?”  It’s a simple question, but there are no simple answers.

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