WLAN - Wireless Local Area Network is a networking technology that allows the user to connect his computer to other ones without any wires. It is called "local" because of its rather small range. On the American market the success is being achieved by Wi-Fi and Wi-Fi5 - these are new-generation wireless networks. The name Wi-Fi, which is an abbreviation of Wireless Fidelity, was created by international organization called Wi-Fi Alliance. The main purpose of its members is examining the compatibility, certifying and promoting hardware designed for Wi-Fi net. Thanks to Wi-Fi Alliance networks built in this way compete with popular Bluetooth technology.Wi-Fi is related to 802.11 standard, which was designed by the Institute of Electrical and Electronic Engineers, and makes basis of WLANs building. According to the standard, wireless communication takes place in Spread Spectrum (SS). It means that the sent signal is distracted to frequency band wider than required for sending information. The 802.11 standard defines several ways of communication between the transmitter and the receiver (these are called modulations): DSSS - Direct Sequence Spread Spectrum FHSS - Frequency Hoping Spread Spectrum IR - Infrared OFDM - Orthogonal Frequency Division Multiplexing.