Why "carnivore" type systems can't be (entirely) open source

[Roland Perry]

 In message <006701c095f2$b3169600$3e0a989e@eloka>, Owen Lewis 
 <oml@eloka.demon.co.uk> writes
>
>----- Original Message -----
>From: "Roland Perry" <roland@linx.net>
>To: <ukcrypto@chiark.greenend.org.uk>
>Sent: 12 February 2001 20:23
>Subject: Re: Why "carnivore" type systems can't be (entirely) open source
>
>>  Analogue cellphones used normal modems, albeit in the rather unusual
>>  format for then - a PCMCIA card. The best data rate to choose was 4,800,
>>  which actually worked better than some of the slower rates. 9600 was out
>>  of the question.
>
>I never was much of a TACS/ETACs user but I did use one in the period 89-92.
>I was not aware that that any could take direct electical input from a
>modem - though there would seem to be no reason why it should not have been
>possible. Why the specification of PCMCIA?

 All the implementations I saw were a cable from a connector on the 
 bottom of the phone (just like GSM) to a PCMCIA card. They were trendy 
 at the time (ie early adopter kit used them, these days some has moved 
 on to USB) but the main reason was that they needed intelligence so they 
 could emulate a Hayes modem. Phone manufacturers didn't build that into 
 the phone itself (when such a small percentage would ever use it) and so 
 it had to be external. A PCMCIA card is more convenient than a "soap on 
 a rope" and serial, to house such a thing.

>Was the feed to the phone not
>from the line side? Acoustic couplers couplers were certainly commercially
>available then and ISTR remained so through the early '90's. One used to see
>them advertised for 'road warriors'.

 I still have such an acoustic coupler, but the ones I saw were more for 
 use on wired-in hotel phones, than mobiles.
>>
>> >Even now, datacom via GSM
>> >is less than ideal. 9600 suks OK.
>>
>>  Yes, it's not that good, which is why I use a 28.8K GSM card these days
>>  (Nokia Data Card with airtime from Orange).
>
>My goodness. You have a 28.8 card or get (near to) 28.8 throughput? If the
>latter I'd welcome details and so might others. How many user sub-channels
>do you have to occupy?

 Yes, I'm using it now. It's called a Nokia Card Phone and uses a 
 proprietary Orange high speed data system. You need three channels for 
 28.8k, but Orange only charge you for one [at the moment; I suspect they 
 may later]. Theres a fiver a month "data supplement" but otherwise the 
 calls fit the normal airtime packages (ie try and use a Geographic 
 number to count as bundled minutes).

 The system does fall back to 19.2K quite frequently, but almost never to 
 9.6K; the card emulates ISDN, so you get very fast connection times, and 
 most ISP PoPs support it. I reckon this technology is about a year ahead 
 of GPRS (aka 2.5G) in terns of rollout. Buy from your Orange Shop. I've 
 added mine to an existing contract as the second user, and am 
 investigating getting it unlocked so I can use a Vodafone SIMM (which 
 would only give 9.6k) for those times when the Orange network isn't 
 available.
-- 
             Roland Perry | tel: +44 1733 207705 | roland@linx.org
              Interim CEO | fax: +44 1733 207729 | http://www.linx.net
London Internet Exchange | mbl: +44 7050 604080 |       /contact/roland