The GPRS packet-transmission mode relies on the "client/server" principle from the computer world, rather than the "calling/called" principle in use in the telephony domain. The client sends a request to the server, which processes the request and sends the result to the client. Thus the mobile may be configured according to the application either in client mode or in server mode.
The mobile may be configured in client mode to have access to the Internet or an intranet or database by initiating a GPRS communication. Usually, the GPRS mobile is configured as a client. Figure 2.1 shows a GPRS MS configured in client mode.
The mobile may also be configured in server mode for vertical application to telemetry monitoring. In this type of application, the mobile may be connected to different pieces of equipment, such as a camera for monitoring or a captor for measurements. The mobile may configure a piece of equipment in order to process the request and then send back the result to the client. In order to interpret a request from a client, the mobile must be able to route information from the network toward the recipient application. In server mode, the MS must be IMSI attached for GPRS services in order to receive the requests from a client.