Len's News, Notes, and Stuff

SMS in an Emergency is No Guarantee of Establishing Successful Communication">Using SMS in an Emergency is No Guarantee of Establishing Successful Communication

Some agen­cies are advis­ing the pub­lic to use text mes­sag­ing (SMS) in a large-scale emer­gency. The ratio­nale is that the voice lines will be over­loaded, but the lit­tle data pack­ets for text mes­sag­ing will get through. Con­cep­tu­ally this sounds nice. In fact, I used to advise this in the past, too. But based on my under­stand­ing of mobile stan­dards and the results of some unplanned tests, I’m not so sure it’s good advice anymore.

You’re likely using CDMA or GSM mobile net­works wher­ever you are in North Amer­ica. CDMA the­o­ret­i­cally has no capac­ity lim­its. How­ever, in prac­tice, capac­ity per cell is lim­ited by the com­puter power present at each base sta­tion. GSM has an upper capac­ity limit based on the chan­nels avail­able and the time slots avail­able per chan­nel. In other words, whichever net­work you’re on, there is a real and finite capac­ity cap.

From what I know, there is no ded­i­cated data chan­nel or ded­i­cated data capac­ity on either GSM or CDMA. Text mes­sage data pack­ets com­pete with voice calls to get through. True, it’s eas­ier to tap Send to try send­ing your SMS through than to redial and Send a voice call, but your chances of mak­ing a suc­cess­ful con­nec­tion remains the same each time.

Fol­low­ing a major emer­gency, every­one who has a cell phone jumps on the net­work and tries to call fam­ily or other loved ones. The net­work is jammed. Most peo­ple are unable to con­nect their calls. If, at this point, you try to send text mes­sages through, you are still com­pet­ing with all the other callers out there — and text messagers.

Now, if every­one sent text mes­sages rather than call­ing, every­one would prob­a­bly get through. One SMS mes­sage imposes a neg­lig­ble load on the sys­tem. Unfor­tu­nately, voice is a much richer, faster way to com­mu­ni­cate and you can’t blame peo­ple for try­ing to make voice calls after an emer­gency. So the real­ity is that the cell net­works will be jammed for voice and for data.

I’ve had two unplanned test expe­ri­ences with this. The first was dur­ing the ini­tial hours of the 2003 Black­out in NE North Amer­ica. The sec­ond was in the first few min­utes after mid­night New Year’s.

Right after the 2003 Black­out hit, the cell net­works were, pre­dictably, flooded and over­loaded. I worked for a cell car­rier at the time, so every­one had a Black­berry already. Some of us had the older Berries run­ning on the Mobi­tex net­work, and some of us had the newer Berries that ran on the GSM net­work. Mobi­tex was RIM’s pro­pri­etary net­work for Berry data. Guess what hap­pened? Nobody could make any voice calls suc­cess­fully with­out try­ing at least a dozen or more times. Those of us on Mobi­tex Berries could PIN-to-PIN mes­sage one another freely, but those of us on GSM Berries were out of luck.

There is no ded­i­cated data net­work like Mobi­tex any­more. All Black­berry data is now car­ried by the GSM & CDMA net­works, and data pack­ets are treated no dif­fer­ently than voice packets.

Right after New Year’s, every­one wants to wish their friends and fam­ily a Happy New Year. My friend and I, inde­pen­dently, fig­ured we’d send text mes­sage greet­ings out and out­smart all the peo­ple try­ing to make voice calls out. Unfor­tu­nately, we both found our phones say­ing the same thing: they were unable to send the messages.

When the cell net­works are jammed, it doesn’t mat­ter whether you’re try­ing to con­nect by voice or data. Capac­ity is shared, and capac­ity is lim­ited. You sim­ply can­not rely on text mes­sag­ing to enable timely, effi­cient mobile com­mu­ni­ca­tion fol­low­ing a major emer­gency. The agen­cies who advise you to do so either do not know any bet­ter, or fig­ure giv­ing you one extra option — no mat­ter how flawed it may be — is bet­ter than nothing.

If you find your­self in a pickle after a major emer­gency and can’t get a cel­lu­lar voice call through, by all means try text mes­sag­ing. You do have a higher chance of get­ting that one mes­sage through in a given time­frame and that is sim­ply because you can retry an SMS faster than you can retry mak­ing a voice con­nec­tion — but know that you are not guar­an­teed to be able to get through just because you’re try­ing to send data.

Con­trary to what some agen­cies are advis­ing, do not count on being able to estab­lish timely, effec­tive com­mu­ni­ca­tion using SMS.