This American Life (on NPR) ran a pretty good documentary on this subject a few weeks back. It's available in Realaudio format on the web. It's an hour long though.
The archive page is
Here.
Or go to the audio directly.
I have a little experience with CDMA. I assume that GSM & TDMA have the same issues.
The problem is that high speed analog modems use phase shift keying to encode the data over the analog phone line. If you make a normal voice call using a cell phone, the data is compressed by your phone and reconstructed in the cell tower using DSPs. This can result in jitter in the reconstructed signal. For voice this is acceptible. But for a data call, the jitter can cause the recontructed sine wave to be at the wrong phase, which would cause misinterpretion of the modem signal.
So when providers such as Sprint or AT&T offer data services, they use a different kind of modem, one that is cellular aware. This kind of modem doesn't send the data as a phase shifted sine wave. Instead it communicates directly with the cell tower in a digital form.
Having said that, I agree that the providers charge too much to make data calls. Basically the phone companies don't charge the true cost of a service. They charge what they think they can charge. It's all about making a buck.
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I heard Tiger Woods is pretty pissed too.
your current version only detects 3 viruses, however the new signature file finds and cleans 5 different viruses.
Wow, based on this data, it seems the number of Mac viruses has jumped by over 66%!
mutt is the best mail client ever.
All mail clients suck. Mutt just sucks less.
Now we are letting inanimate objects raise our kids!
/ 103-7935959-6326214
But you can buy one of these today:
http://www.amazon.com/exec/obidos/ASIN/B00008GYCZ
This American Life (on NPR) ran a pretty good documentary on this subject a few weeks back. It's available in Realaudio format on the web. It's an hour long though. The archive page is Here. Or go to the audio directly.
I have a little experience with CDMA. I assume that GSM & TDMA have the same issues.
The problem is that high speed analog modems use phase shift keying to encode the data over the analog phone line. If you make a normal voice call using a cell phone, the data is compressed by your phone and reconstructed in the cell tower using DSPs. This can result in jitter in the reconstructed signal. For voice this is acceptible. But for a data call, the jitter can cause the recontructed sine wave to be at the wrong phase, which would cause misinterpretion of the modem signal.
So when providers such as Sprint or AT&T offer data services, they use a different kind of modem, one that is cellular aware. This kind of modem doesn't send the data as a phase shifted sine wave. Instead it communicates directly with the cell tower in a digital form.
Having said that, I agree that the providers charge too much to make data calls. Basically the phone companies don't charge the true cost of a service. They charge what they think they can charge. It's all about making a buck.
I scanned in my copy of the first and last page of the letter I got from Deloitte & Touche. See them here: http://www.geocities.com/pancake_1968/main.html