The introduction of the GPRS modem’s working principle:
The communication between the modem and the server is initiated by the GPRS modem (client), and the server responds to the modem by sending back feedback or accepting communication. The modem side and the server side jointly form an application system based on GPRS and INTERNET network communication. Compared with the modem side, the server side installs more complicated application programs, it can accept any communication request initiated by the modem and detect the communication status in the link at all times, thus realizing real-time data collection, database service and other applications.
The modem needs to know the IP address and port number of the server in advance, and then can initiate a communication request. Once the communication is established, there is no difference between the server and the modem.
The IP address of the server can be either a public IP address (fixed IP) or a dynamic domain name obtained through a domain name resolution server.
The port number of the server usually corresponds to a specific application running on the server, for example, port number TCP 21 is used by the FTP service, and TCP 80 is used by the hypertext server (https). That is, the server-side application supports sending and receiving data through a specific port number.