GPRS - fairly off topic

Jeff LaCoursiere jeff at
Fri Sep 6 16:12:55 BST 2002

The operators DO assign an IP to your phone when you login to the
gateway.  Incidentally at least DT's operators (One2One, Vodaphone) use
PPP for GPRS AND WAP.  The IP you get assigned is out of a gigantic pool
of private addresses.  Your traffic travels through a web proxy if you are
doing CSD (WAP), and therefore the address seen in a remote WAP site will
be that of the gateway, not your phone.  If doing Java downloads or MMS
your traffic instead travels through a NAT firewall cluster, thus in the
remote site the firewall's external address will be seen rather than the
IP in the phone.

Depending on your operator you may or may not be able to make direct IP
connections on strange ports or with protocols other than TCP.


On Thu, 5 Sep 2002, Jon Schneider wrote:

> I may be shortly asked by a colleague to do something useful with a pair of GPRS 
> modules (Erickson GM47 and a Siemens MC35) and have a number of questions. 
> Posting here seems like my best bet to get some knowledgeable answers. (I don't want 
> to be told to click on "My Computer".)
> My colleague seems to think the modules talk PPP but has not managed to get 
> Vodafone's ConnectMe software (designed for phones) to talk to them. I don't know 
> whether this should work or not. I'm thinking about using Brian's ppp to experiment. 
> Ultimately we'll be lashing these modules to small micros along with GPS and other 
> stuff. Then I'll need to come up with some lean mean code which is just enough to do 
> the PPP and compose UDP packets.
> Does being connected through a typical (well Vodafone's or Orange's) GPRS service 
> give one an IP (v4) address ?  If so won't the operators rapidly run out of them ? Or are 
> they NATing or proxying ? Obviously IPv6 would be better. What exactly is the cost 
> based on (amount of TCP/UDP data or the whole PPP frame) ? What's to stop a third 
> party squirting junk data and running up a huge bill ?
> 	Jon
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