802.11 Wireless LANs

A wireless LAN is a LAN that utilizes radio-frequency communication to permit data transmission among fi xed, nomadic, or moving computers. Wireless LANs can be divided into two operational modes: infrastructure mode and ad hoc mode, depending on how the network is formed. Most wireless LANs operate in infrastructure mode. In many cases, a wireless LAN is used to avoid the hassle of establishing a wired LAN (e.g., cabling in a multiroom building or a large open space such as a warehouse or a manufacturing plant). Several computers are connected over the air to a central AP that in turn links to the wired network. At the same time, a laptop computer with a wireless LAN interface is able to access the backend wired network across different APs in an intermittent or real-time fashion. In all these scenarios, a wireless LAN infrastructure of networked APs is needed. These APs may connect directly to each other via wireless links or rely on the wired network for interconnection.

Ad hoc mode is more flexible than infrastructure mode in that it does not require any central or distributed infrastructure devices or computers to operate. Instead, computers in an ad hoc wireless LAN temporarily self-organize into a group to serve each other in a peer-to-peer manner. In some cases when it is not feasible to build a network infrastructure for technical or other reasons (e.g., troops on the battlefield or sports spectators in a huge stadium), an ad hoc wireless LAN seems a good solution.

Today, the dominant radio-frequency technology used to build a wireless LAN is a spread spectrum on the unlicensed 2.4-GHz frequency band, as defi ned in the IEEE 802.11 standards and ETSI HIPERLAN (High-Performance Radio Local Access Network). Other radiofrequency technologies such as infrared wireless LANs and narrowband microwave LANs have faded away following the explosive growth of spectrum wireless LANs. The following is a list of advantages of radio-frequency wireless LANs over infrared; narrowband microwave LANs are not considered because they are primarily used for PTP wireless communication rather than group communication:

● High bandwidth: 802.11 wireless LANs support a link bandwidth up to 11 Mbps for 802.11b and 55 Mbps for 802.11a and HIPER-LAN2, much higher than that of infrared, which is only up to several megabits per second.

● No LOS restriction: Infrared requires LOS for transmission, but radio does not as long as the frequency in use is not too high. This is the major reason why 802.11 wireless LANs are the number one choice for home networking.

● Easy to set up and use: The 802.11 protocols are designed to allow almost zero configuration of the network and the interfaces. Of course, the default setting is by no means secure but it does work.

Source of Information : Elsevier Wireless Networking Complete 2010


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