Off-line and awakenable monitoring system for voltage of electric power based on GPRS

The application taking GPRS as the methods of communication would suppose that the terminals based GPRS are always on-line and they actively call server for establishing the links of GPRS. An applied mode of GPRS technology that needn't the terminals based GPRS to be always on-line but to be awaken in time of need is presented. The applied mode bring bidirectional data transferring that doesn't use unchanged IP addresses of Internet to success,and it is applied in the monitoring system for the voltage of electric power.