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Aggressive IM App Took Down T-Mobile Wireless

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October 26, 2010

Aggressive IM App Took Down T-Mobile Wireless

By George Ou, Policy Director, Digital Society

Mike Dano has an interesting story on an Instant Messaging (IM) application that brought T-Mobile’s wireless network to its knees.  Based on this FCC filingby Grant Castle, director of T-Mobile’s national planning and performance engineering, Castle explained how an Android (News - Alert) based IM application’s aggressive signaling behavior caused a massive amount of congestion affecting all users on a node.

What was interesting to me was the fact that the developer of that application tested on a WiFi (News - Alert) network with no problems, but it was too much for the mobile network.  WiFi networks also have severe packet rate limitations were only four Voice over IP (VoIP) users or three Apple (News - Alert) Facetime calls will fill the packet rate limit.  But because there’s generally a few users on WiFi (especially home networks), it’s not a big problem.  But on a wireless node that serves hundreds of users, a single aggressive application with a frequent packet rate can cause severe problems even if it doesn’t use a lot of bandwidth.

Of course the problem is even worse if the packet rate and the bandwidth rate is high such a P2P application.  There are people concerned about the fact that wireless networks ban applications like BitTorrent, and others in the Net Neutrality movement that wants to see the practice abolished.  But if networks can’t support them without being brought to their knees, do we force the networks to support these applications anyways?

If signaling problems from a single IM app is bad, try running BitTorrent on a wireless network with 50 concurrent TCP or UDP (News - Alert) connections going full throttle.  If BitTorrent brought my WiFi network and broadband network to its knees adding hundreds to thousands of milliseconds of jitter, how would all the customers being served by a cell tower feel if I ran BitTorrent (News - Alert)?  This is why I keep saying that we can’t pretend that wireless networks are the same as wired networks.  We simply can’t regulate our way out of technological limits.

Even as bandwidth increases on wireless networks, the packet rate limit will still be a major constraining factor.  Those networks will still have to be managed and that will include precluding certain applications.  We might get to the point where the wireless network are eventually intelligent enough to actively communicate with the clients to limit their packet rates and bandwidth based on equitable distribution of bandwidth and packet transmission opportunities. Then it won’t be necessary to have blunt application ban policies, but wireless networks haven’t gotten to that level of intelligent management yet.  Until then, the application bans must remain in place.

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