There's a fascinating article over on Ars Technica suggesting that the problems faced by AT&T (NYSE:T, news, filings) by iPhone-induced congestion aren't actually due to insufficient bandwidth capacity at all. Rather, the issues may stem from the design of the iPhone itself. No, not the part that makes it easy and fun to burn bandwidth and thus leads to higher data usage rates, oddly enough they mean the part that saves battery life.
In simplified form, the iPhone and other smartphones don't leave open a data connection with the cell tower when users are browsing or reading email. Rather, they open and shut such a connection for each burst of data. So one 15 minute session of browsing could involve hundreds of new connections being set up. The problem is that to set up connections - whether voice, sms, data, or whatever - cell networks use the same signaling channel. If there are too many smartphones in one area, this signal channel can become overloaded by all the opening and shutting of data connections long before the full data capacity of the cell is reached - causing not only slow access but dropped calls and other issues. Hmm, that does sound familiar.
Now, if this is true and AT&T now knows it, it explains a great deal. For instance, if their network were bursting at the seams due to raw data volume, their recent actions to allow Skype and the Sling player might be like pouring gasoline on a fire. But while these applications might enable customers to gleefully burn more bandwidth, they probably don't burn any more signaling than other applications - perhaps less actually since they may keep connections open longer. If AT&T will soon have its network reconfigured to handle signaling the way most European carriers do, then they wouldn't be worried about being drowned in a flood VoIP and video bits.
Hmmm, I wonder how Sprint and Verizon Wireless configure this. We may never know, as they have time to learn from AT&T's iPhone travails before their own smartphone data usage reaches similar critical levels.
I also wonder just how much bandwidth iPhone users will burn if they aren't being held back by AT&T's network issues. We may find out soon.