GPRS - fairly off topic

Roger Hardiman roger at
Thu Sep 5 22:05:03 BST 2002

(well this is not off topic for me :-)

I'll speak for Orange as I work closely with them.

> Does being connected through a typical (well Vodafone's or Orange's) GPRS
> give one an IP (v4) address ?
> Or are they NATing or proxying ?

GPRS gives you a 172.x.x.x IP address which is behind NAT.

> What exactly is the cost
> based on (amount of TCP/UDP data or the whole PPP frame) ?

The PPP only runs as far as the handset / GSM device. The billing is the
data which goes over
GPRS which would just be the actual data.
Although I've never checked a GPRS bill to confirm this.

>What's to stop a third
> party squirting junk data and running up a huge bill ?

On orange, everything is firewalled to prevent this
GPRS users cannot send any traffic to other GPRS users
even when they are on the same 172.x.x.x subnet.
And due to NAT, no one can get to you from the outside world.

So, the only way data can get to you is when you open a TCP socket and data
can flow along
that socket.

There no UDP support either.

For FreeBSD and GPRS, I've got the PCMCIA GlobeTrotter card from Option
I can borrow a Sierra Wireless 750 card too to test.


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