1, because the mobile phone is in arrears, there is no signal, and the mobile phone does not open the data network, resulting in the data link being blocked. 2. It is because there is a problem with an APP server that the network link cannot reach the server. 3. The mobile phone chain is connected to the WIFI signal, but the WIFI signal is not actually connected to the Internet, so it is not linked to the APP.
Serer refers to a node computer that provides services for customers' requests in a network environment or a distributed management environment with a client-server structure (see client-server computing), or refers to computer software running on the computer for managing resources and providing services for users.