Dan York, Director of Emerging Communication Technology at Voxeo, but also on the Board of the Voice over IP Security Alliance (VOIPSA) has written two excellent pieces in another of his blogs, Voice of VoIPSA, discussing the blocking of VoIP calls by Aircell. The first explains how they can block Skype calls, even though they are encrypted while the second goes on to explain why Andy Abramson could make a VoIP call using Phweet.

1. How Aircell is (probably) blocking VoIP phone calls on planes (hint… VoIP Whack-A-Mole)

There it is… all in UDP… and coming in at about 100 packets per second. And if I look at the actual Wireshark traces, I can see that these 100 packets per second are all very tiny sizes. Many of them are between 37 and 50 bytes.

And this is an encrypted Skype call!

No need to decrypt it. Just see that it’s a steady stream of 100 very small packets per second (50 packets per second each way) all over UDP.

Kill the stream. Block it. Conversation dead. No more VoIP on the plane.

It’s basically the network security version of Whack-A-Mole. See a VoIP stream start up… block it. See another one… block it. See yet another… block it. Whenever anything pops up that meets the profile, stomp on it.

This explains, too, why people could talk for a few seconds and then had their conversations terminated. The pattern has to appear in the network monitoring software. The software has to be sure it’s a VoIP stream and not something else… and then the software can block it.

Now I don’t know for a fact that this is how Aircell is blocking VoIP, but it would be easy enough to do it this way.

2. The reason why (probably) you can use Phweet on a plane when Skype is blocked

And there you go… one very possible reason why Phweet may work and Skype, Sightspeed and others were blocked is simply this:

The Tringme Flash-based softphone is sending audio over TCP and Aircell is not recognizing and blocking VoIP calls over TCP.

Or at least Aircell wasn’t blocking TCP. (They probably are by now or will be soon.)

Now to be fair, if Aircell isn’t blocking TCP, this was probably a decent assumption to make. I mean, the typical mindset to date has been… who in their right mind would send audio streams over TCP?

In all the VoIP systems I’ve worked with, I can’t think offhand of any other systems that send audio over TCP. As part of its range of tricks to get through firewalls, I understand that Skype can use TCP if it is unable to send over UDP, but I’ve never captured it doing so. The IP-PBXs I’m familiar with, both commercial and open source, all send RTP over UDP.

Read the entire posts for the details of Dan’s assumptions and explanations. One of Dan’s writing strengths is his ability to make technology understandable to the lay person.

As for not wanting to have voice calls available in flight I would soften my stand if human nature would change. Over the weekend I was reading a book on the history of one of our rural independent telephone companies where they were providing anecdotes about early usage of the operator-serviced telephones:

Mrs. Alice Cooley’s brother, Billy Huang, Tiverton, used the phone for the first time to call his chum a few houses down the street. Alice and some others were out in the garden and they heard Billy shouting loudly on the phone. He thought he had to shout to be heard. Some people never did get over the idea that they had to shout on the phone.

From “Bruce Municipal Telephone System – A Long Line of History 1910 – 1994″ by Anne Duke Judd.

Enough said. Thanks, Dan for taking time to put up these explanations.

Tags: Dan York, Aircell, Skype, GoGo, Andy Abramson, TringMe, Phweet

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I’m constantly amazed at how some mobile phone users insist on having their cell phone conversation take priority over social niceties such as paying attention to the cashier at a store checkout, yakking out loud in an airport (or doctor’s) waiting room, or worse still, due to the implicit safety issue, holding the phone on the shoulder while trying to drive with your head sideways. Dan York got to listen to one side of a few conversations during his train trip home from New York yesterday. Basically I consider these people to be inconsiderate and rude.

I also find that over 85% of my Skype activity involves chat; it’s unobtrusive, relatively private with respect to people around you and provides a simple, effective and much less annoying means of communicating with remote work colleagues and friends.

So it’s no surprise that AirCell, who is installing Internet access on several U.S. airlines’ aircraft, is allowing passengers to chat but not talk during flight. I have to go along with their excuse for not allowing voice: “the consideration for passengers who want peace and quiet”. My hope is that we never see in-flight (cellular or VoIP) phone use allowed.

However, Andy reports on an experience where Phweet may provide a path for voice conversations using a Flash player. American Airlines passenger and Laptop Magazine reporter Joanna Stern, with whom Andy completed the “in-flight” Phweet call, also comments in her very detailed log of her AirCell in-flight Internet experience:

I couldn’t agree more. I was getting stares right and left in the 5 minutes I was talking to Andy and I don’t blame the passengers of American Airlines at all. Granted I was talking really loudly without a headset, but loud talkers on a plane (and in general) are annoying. The poor girl next to me was trying to sleep. Other than the call, I haven’t bothered her once. Though, she thinks I am a total geek.

On the other hand she was chatting with Aircell CEO Jack Blumenstein via Skype throughout the flight.

As for the the restriction on VoIP he says, “Fundamentally it is a reaction to widespread passenger aversion to the idea of many people talking loudly on flights (as we’ve all often experienced before take-off or while landing).”

So will AirCell figure out a way to avoid VoIP over Flash without cutting off all otherwise acceptable Flash traffic?

(And, as for those “Skyphones” that we used to see on aircraft – at some exorbitant cost of several dollars per minute – they got little use and calls were quite short. In the year I flew over 150,000 kilometers on Air Canada I used them once due to a rerouted landing caused by last minute weather conditions at the destination airport.)

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When I received this Twitter message earlier this afternoon:

clicked on the embedded URL and immediately was listening in on a conversation involving not only Stuart Henshall but also David Beckemeyer of Televolution (producer of PhoneGnome – now known as the PhweetGeek), I found I was in for a most interesting conversation experience. Within minutes we had a multi-party call involving as many as eight participants from India, Italy, Ireland (actually, Pat was calling in while on vacation in Spain) as well as others in the U.S. They had all joined “spontaneously” from a Twitter message (in my case initially seen via Twitter4Skype) as Stuart and David launched an Alpha version of Phweet this afternoon.

First thoughts and comments:

• The immediacy – send the URL via Twitter and any of your Twitter Followers can join with three clicks – the URL, the TringMe VoIP Flash Player widget and the “Allow” button within the Flash Player. At that point the call host needs to “accept” your request to join and you’re into the conversation.
• You monitor the call participants and participate in a chat session via a web page with a URL dedicated to the specific call (www.phweet.com/[four character call code]). When the host ends the session, the URL dies also; however, tweets are the only traces left of the call.

• It’s a mashup of Twitter, TringMe, and SIP-based services all hosted on a Televolution server.
• While, if you just send out a general Tweet all your Followers can join; you can Direct Message an individual, or individuals, if you want a totally private call.
• You can join from a browser or a SIP ID; for instance Pat Phelan (of MaxRoam fame) called in from a Nokia N95 via his Truphone SIP ID (Truphone number@truphone.com) but you can also join in from Gizmo 5 and other SIP-based services.
• It’s Alpha: TringMe would periodically drop the call connection but a web page refresh would bring back the Widget button and you could instantly be in the conversation again.
• It’s Alpha: when I attempted to host my own call with Stuart as the invitee, we could “see” each other on the related web page but the audio connection did not work.
• Joining a conversation actually involves a call out from the Televolution server; as a result they are only working with connections that do not involve termination charges. Eventually they would like to have a way to join from, say, a mobile phone while letting another party worry about the back office transactions.
• Call quality was quite good; David needs to up his mic volume but other parties were very clear. On the other hand there is no echo cancellation capability, so headsets are a requirement unless you have echo cancellation hardware embedded into your mic.
• This is totally an Internet based service: effectively your Twitter followers are the directory; there is no other form of intermediation, such as a softphone client, involved in setting up, and participating in, the call. It does require you have the Adobe Flash Player installed.
• It’s Alpha: Stuart and David are still going through the discipline of defining a basic feature set.

Stuart and David are inviting Twitter members to give it a try; they want user feedback before even calling it Beta, to ensure it at least has all the basics of a service that provides reliable connections, total host control (for instance, they need to add the ability for a host to remove a participant) and meets basic call support needs. Overall it looks to be a promising concept and a unique “click-to-call” service that supports ad hoc social networking.

Other posts:

• Stuart Henshall: Why Phweet?
• Stuart Henshall: Who created the Phweetman?
• Pat Phelan: Phweet.com Talking on Twitter
• Phil Wolff: Phweet public alpha – from tweet to talk in one click
• TechCrunch: Call your Twitter pals with Phweet
• All public Phweet sessions

Tags: Phweet, Stuart Henshall, David Beckemeyer, Twitter, Televolution, TringMe, Pat Phelan, Truphone, Nokia N95