Greg Rose wrote:
The three different digital standards in North America are TDMA, CDMA, and GSM (in NY and DC only AFAIK).
GSM is also a Time Division Multiple Access (TDMA) system. In it's original form it uses specrum around 900 MHz, which I believe not to be available in the US. Shame really, I can roam with my GSM phone over pretty much the rest of the planet ... except the US. Anyway, there are two higher frequency derivatives, PCS1800 & PCS1900, which have been deployed in the US. I'm not involved directly in the US market so I'm not sure where. I assume however that these are the systems to which Greg refers.
Newer analog phones use at least some of this, but I don't know much about them. I'll ignore GSM. ^^^^^^^^^^^^^^^ Aww shame ;)
The conclusion is that neither way of doing it is truly cryptographically strong, but both are a lot better than listening to Princess Di call Newt "Squidgy" on a Radio Shack scanner.
GSM uses the A5 algorithm which *is* cryptographically strong, but is unfortunately considered to be top secret stuff. If, however, you were to pick up a copy of "Applied Cryptography, 2nd Edition" by Bruce Schneier you may find something of interest. I hope that you'll work out from my .sig why I can't say much more. Hope this helps Andy M -- ___________________________________________________________________ Andrew Meredith Senior Systems Engineer Tel: +44(0) 1793 565377 Network Engineering Tools Grp Fax: +44(0) 1793 565161 GSM Products Division Page: +44(0) 839 421153 Motorola SMTP: meredith@ecid.cig.mot.com 16, Euroway, Blagrove X400: QSWI016@email.mot.com Swindon, SN5 8YQ, UK SMS: 44860608008@sms.telco.mot.com ___________________________________________________________________