On 2015-11-14 23:59, Yucong Sun wrote: > This is what roaming data means, Your data packet is simply trunked to > your original operator to process. So you will be having a US ip on > the web.
Based on my understanding, the phone establishes a local IP aconnection with equipment associated with an antenna and gets an IP a from it. It then establishes a tunnel to the APN operated by your carrier and the tunnel gets the IP address that your apps see/use. The IP address your apps see/use is given by your home carrier and all packlets flow through your home carrier's APN before going to the internet and you use your home carrier's DNS. Where I am unclear is what happens when you move from tower to tower. Whether your local IP changes and the tunnel is transparently moved to the new local IP, of whether the local IP address moves with you and routing tables are changed. Some phones have "debug" modes that will show both the local (local antenna) and the public IP address (from APN) in use. As your traffic flows out of China, it passes through the "great wall of routers" as traffic between you and your carrier's APN, not between you and some banned site you are trying to access. They'd have to do DPI and possibly decrypt tunnel traffic to catch where you are trying to connect and block those.
