Internet access through GPRS/UMTS

September 23, 2009 at 03:22:09
Specs: Linux
Hi All,

Can you please tell me if when we connect a mobile phone to ISP through GPRS/UMTS, do you get a new IP everytime you connect to internet? ISn't dial-up with modem having this by security policy to give a new IP whenever you dial in to ISP? Is this also true for mobile phones ovr cellular network? I know that broadband internet through say DSL would work on an alwas on policy that the IP address doesnt change everytime you reconnect.
If so, in a cellular network why would you have a new IP for every connection? By giving our username and password to ISP through moible, are we not making a PPP connection from our mobile phone to ISP? What is actually happening when you give username password details to ISP technically??? do please explain.

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September 23, 2009 at 05:10:27
You almost certainly do get a different IP address whenever you connect a mobile phone. You may occasionally get the same IP address back, it depends on how big the ISPs DHCP pool is.

Getting a different IP address every time you connect has absolutely nothing at all to do with security. It has a lot to do with sharing a limited number if IP addresses to the maximum number of users. If every registered user to an ISP tried to connect simultaneously the chances are they would run out if IP addresses and somebody would have to wait till one became available.

Slightly different with an always on connection like broadband but you are still likely to get a different IP address unless you have been allocated a static IP address which usually costs extra.

By the time you get round to entering the user name and password the PPP link is already established. The PPP link is established automatically as soon as you press connect. The user name and password is to allow you access to your ISPs network.


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September 23, 2009 at 05:31:50
Thank you Stuart.
Just a little curiosity. Don't the DHCP servers normally have lease time? Could it it be other way like a Radial server providing IP? I disconnected and connected my cell phone within 2 seconds and I still got a new IP. I wonder if the ISP doesnt have any history of such details in the case of GPRS

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