Secrets of mobile Internet access 1

Currently, smartphones all have 3G and WiFi functions. By default, WiFi is used. Why can 3G be deactivated after WiFi access? In fact, it is not disabled, but the default route is changed. The 3G group network still exists. There is a phenomenon that can be revealed. For example, if you access a company's internal Wi-Fi hotspot, And the WiFi is just an internal network, you cannot access the Internet, at this time, your mobile phone shows that you are using WiFi instead of 3G. However, you can still get the information pushed by mzone, QQ, and other applications. If the network card of the 3G group network is down, how is this information pushed? In fact, only the local default gateway is changed to a Wi-Fi hotspot. There are still routes from other locations to the local machine! However, at this time, the communication between 3G networks is one-way. When you receive a message, you can't wait to view it. However, you are notified that the connection fails, because the Internet cannot be connected in the upstream direction... in the opposite downstream direction, the Group network is always 3G. If the downstream traffic is also billed