套接字编程WiFi问题

Question

I am implementing a mobile chat application, I am using socket connection for implementing p2p connectivity. My chat is working fine with android devices. My issue is I can connect a device in 3g network or with in the same WiFi network but the connection is not working when a device form outside WiFi try to connect a device in the WiFi network. I know it's because of the local IP of the device assigned by the WiFi. How can I root and connect a device in the WiFi?

Answer 1

Sounds more like a router settings issue, than an app issue (meaning that users of your app would need to do this for their own networks as well).

Your wifi router needs to know how to forward communication to your device. So say that your app is connecting on port 1234, then you need to tell your router to forward communication from the outside on port 1234 to the internal IP of your phone in your wifi network.

The phone that is outside of the network should target your network's external IP and port 1234.

Answer 2

Sajan, your issue is not only an IP mapping issue, but also a NAT traversal issue. It is not always possible to punch holes in NATs. And when it is, it must be done with some sophisticated techniques including a super peer located outside of your wifi/lan which will read the translated address from your inside peer.

Unless you are using UDP and the NAT is friendly, it is not possible to send TCP communication directly to the inside peer. In most case, you'll have to check what is possible with the NAT, and if there is something possible, you'll need to perform mapping prediction and tell both peer to attempt com on predicted IP addresses.

That's valid if you don't want you users to have to configure their NATs. And even in that case, such configuration will not always be enough (if there are cascades of NATs, or proxies for example).