How the Greek cellphone network was tapped.

[Bill Stewart]

At 10:59 PM 7/9/2007, Florian Weimer wrote:
>Uh-oh, no.  The protocol characteristics don't change depending on
>who is selling you the device.

Of course they do, at least in the US,
where the mobile phones are generally carrier-specific,
often locked, and generally don't have open designs.
In particular, they're not usually designed to let the
data applications get at the voice compression ASICs,
but they usually don't have enough CPU to compress voice in Java
if they can get at the voice stream at all.
Some of the PDA phones are more flexible, and I'd expect
OpenMoko to be much more flexible.

>Many telcos have an aversion to end-to-end protocols.

They're getting better about it, but the transmission characteristics
from most of the data protocols aren't designed for voice,
unless you're willing to do push-to-talk or equivalent.
So ironically, if you want to get good latency for 5.3kbps voice,
you'll want the fastest data protocols.
HSDPA's latency is 100-200ms, and upstream is 100+ kbps -
you could probably run uncompressed voice which is about 80kbps,
since latency's less of a problem.
(EDGE has upstream of 40-60kbps, but latency is 350+
so the more compressed protocols aren't going to behave.
I don't have the 1xRTT numbers handy, but I think they're similar.)




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