Overall, this is an fairly well researched article, I would normally expect a lot less from a newspaper article. Unfortunately, the author bases much of his argument on a single nugget, that text messages are transmitted in a control channel, and does not fully investigate or explain what that precisely means. Because the author did not dig deeper, the article loses a lot of meaning and falls flat when you fully understand how GSM utilizes control channels. The lynchpin of the article:

Perhaps the costs for the wireless portion at either end are high — spectrum is finite, after all, and carriers pay dearly for the rights to use it. But text messages are not just tiny; they are also free riders, tucked into what’s called a control channel, space reserved for operation of the wireless network…

…Once one understands that a text message travels wirelessly as a stowaway within a control channel, one sees the carriers’ pricing plans in an entirely new light.

By their very definition, Control Channels are vital to the process of setting up any cellular voice calls—and, I think, data transfers. Thus, more text messages being transmitted at any given time, the less control channels are available for individuals who wish to make a phone call. If all control channels are unavailable, the base station cannot give your phone the frequency, encryption, and additional parameters to start a phone call. You’ll get the dreaded “call failed” error on your phone. The author is correct in that the utilization of these channels is brief, but with trillions of these things being sent, things can get hairy quick, especially in high-density settings.

So an increasing (especially exponentially) amount of text messages imposes a real cost on carriers in terms of ensuring that cell towers that process large volumes of text messages and traffic have enough control channels.

This could imply the requisition, installation, and maintenance of additional hardware radios. These are not cheap (several thousand dollars each). In addition, if traffic is at extremely high levels and the cabinets at that base station are full, then a carrier may even have to install a whole new tower (or colocate on an existing tower) in the area which can cost upward of $100,000.

In a small market, the costs of keeping up with traffic in this way can be millions of dollars a year. In large markets like Chicago, Houston, Atlanta, New York City, and LA it can be tens of millions and higher.

Now, with all that said, SMS’s are still a small bit of the pie when it comes to data transit costs but that’s not really the issue. Obviously data transfer and voice calls use up a lot more bandwidth. I would reckon, though, that the relative frequency of text messages vastly outnumbers each and imposes an unbalanced penalty on control channel contention at any given time.

Posted on: 2008 Dec 28