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It works because cellular roaming traffic travels over a tunnel to your carrier's source country. This greatly simplifies data billing calculations, since they
by tristanj 9y ago
It works because cellular roaming traffic travels over a tunnel to your carrier's source country. This greatly simplifies data billing calculations, since they only have to keep track of the usage of one connection.
The traffic is already tunneled when it passes through the GFW.
- schuke 9y agoSo I guess the reverse is true also, which explains why my mainland SIM card wouldn't have unfiltered access roaming in HK.
- tristanj 9y agoI believe so. When I was in China, my mainland SIM didn't work at all in HK. I assume many people get prepaid SIMs when traveling out of China so they wouldn't be subject to filtering anyway.
- em3rgent0rdr 9y agoIsn't this effectively a VPN? Or is the traffic not encrypted?
- tristanj 9y agoYes, effectively a VPN but I would just call it a tunnel, I don't think it fits the definition of a VPN. I'm not sure if this traffic is encrypted (I assume it is), but I know GFW filtering happens at egress points so mobile traffic would already be tunneled by then. They could add dedicated hardware at mobile towers to GFW this traffic but I don't think the govt sees a need to. The primary target of the GFW is to stop Chinese citizens from accessing foreign services. Foreigners on foreign roaming data plans are not the intent of the GFW. My bet is that they could filter this, but it's not worth the infrastructure investment.