Figure 2 shows a typical implementation of a sensor network using a GSM (Global system for mobile communication) modem. Here all of the sensors communicate their data to a centralized server. The server has control over individual sensor nodes; however, individual sensor nodes cannot communicate between themselves. The server has to be involved for any communication between any two sensor nodes.
GSM (Global System for Mobile communication) is one of the standards for mobile telephony in the world. Although initially used only for voice communication, it has been adapted to include data capabilities by means of GPRS (General Packet Radio Service) and EDGE (Enhanced Data Rates for GSM Evolution). A GSM modem is a type of modem which accepts a SIM (Subscriber Identification Module) and operates like a mobile phone. GSM modems can be used in low power mode or can also be turned off when they are not in use. The cost of transmitting data by GSM networks is has been falling rapidly. What’s more, a GSM modem can easily be interfaced to microcontrollers using standard communication protocols. Mobile phones are increasingly handling data along with voice. Most GSM modems have a TCP/IP stack implemented on them and can be used to transmit data over secure channels. This also reduces the complexity of developing applications and enables the use of simple microcontrollers to interface to the GSM modem.
A GSM modem can connect to any IP (Internet Protocol) address and transmit data. Multiple modems can send data to a single IP address, and all the data can be