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When my cellphone accesses a website via the tower and its GPRS gateway, NAT ensures that the sites receive a public IP. Would all phones using a single tower have the same IP?

  • If yes, then how can the mass of received HTTP data routed to the correct cellphone? And how can websites differentiate between cellphone visitors? Is there additional HTTP header data?
  • If no, then how are these unique IPs assigned? Based on availability or location? Would each tower have a fixed set of IPs?
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If you happen to have an Android phone, you can check your local IP in settings -> status, it's most likely 10.x.y.z. Then visit whatsmyip.org to see your public IP. Then compare it with a friend's phone who has the same provider. –  ott-- Sep 27 '13 at 18:06

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up vote 4 down vote accepted

To answer your first question mobile/cell-phone IP addresses are handed out using DHCP like any other client device. To answer your second questions, well yes, through NAT - that's what NAT does, it allows multiple 'inside' devices to get IP services through a NAT gateway - external IP services will not be able to identify individual internal devices like phones by IP but could via a session ID, cookie or similar.

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I'm a little confused, would all phones using a tower have the same public IP address? yes/no? –  Jarvis Aug 29 '09 at 19:23
3  
Provider dependent. There's no reason they have to though. –  Cian Aug 29 '09 at 19:26
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I thought most cell phones use PPP, and so they don't actually use DHCP but instead get their IP from the remote end of the ppp connection... –  chris Aug 29 '09 at 23:17
    
You're right, at least for all the providers in ie. –  Cian Aug 29 '09 at 23:53
    
Correct, the traffic only turns into IP in a one or only a few centralised locations - it isn't IP traffic at the tower. –  Chopper3 Aug 31 '09 at 10:09

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