Wireless Local Area Network enables users to communicate without any cabling. However, devices on these wireless Local Area Networks need to communicate with the devices on the “wired LANs,” so this seemed like an appropriate place to cover the basics of wireless Local Area Networks.
Wireless communication happens all around us-literally. Cordless phones are relatively common, with communications between the phone and the base unit happening using radio waves. Similarly, mobile phones use radio waves to communicate to a transmitter and receiver on a cell tower nearby. Your TV remote control even performs some basic wireless communication using infrared waves.
Wireless communication uses some form of electromagnetic energy that passes through space. The energy propagates through the air at varying wavelengths. Depending on the wavelength of the energy, the energy might be visible or not. Given the large number of applications for wireless in the world, different wavelengths of energy are given different names, such as infrared for one range, radio frequency for another, and so on.
Electromagnetic energy actually can pass through matter, but often the matter reflects the energy to some degree and absorbs part of the energy as well. Some wavelengths require a line-of-sight for communication to happen because the wavelengths do not pass through matter well. For instance, a TV remote control using infrared typically requires a line-of-sight.
Others, such as the wavelengths used for your cell phone, do not require line-of-sight but are affected to some degree by the number, thickness, and materials in the obstructions the phone and the cell tower. Many of you have probably walked around a building trying to find a place with good reception for your mobile phone-the problems are caused in part to the building absorbing and reflecting some of the energy.
Wireless Local Area Networks have become hugely popular in companies as well as in the home. The beauty of all wireless communication, including wireless Local Area Networks, is the lack of wires. No cables are required, and there’s no need to open up walls, get a ladder to get up in the ceiling, or pay $100 plus per cable to get new cables run. The downsides relate to the speeds (generally less than those of wired LANs today), security risks (anyone nearby can attempt to eavesdrop), and the extra engineering effort (such as MIMO technology) to make sure you have enough coverage in the area in which you allow people to roam with their wireless devices
IEEE 802.11 Wireless Local Area Networks
The most popular type of wireless Local Area Network today is based on the IEEE 802.11 standard, which is known informally as Wi-Fi. The 802.11 specification defines what happens on the wireless network to let two or more devices send and receive data.
Wireless Local Area Network communication is really a shared LAN because only one station effectively can transmit at one time, at least in a particular constrained geography. 802.11 signals effectively might reach another device as far as 300 feet away. So, you can have lots of people around the planet using the airwaves for 802.11 at any one point in time, but only one device can send at a time when within range of the wireless signals. Wireless Local Area Networks typically include one or more computers that have a wireless 802.11 LAN card, plus one or more wireless access points (APs). Access Points Bridge or route traffic from the wireless Local Area Network to the “wired” LAN and vice versa. On the Figure below, wireless access point depicts the general idea. See also the concept of networking bridge.
Wireless LAN
The AP shows two antennae protruding from the corners-indeed, a component of wireless communications is the antennae used to receive and transmit wireless radio signals. The two laptops with the Wi-Fi devices also have antennae (which is usually internal antennae), typically connected to the end of the 802.11 LAN card and protruding out from the laptops.
Note that 802.11 calls for the use of IEEE 802.2 LLC, as well as the same format of addresses defined in 802.3. 802.11 does use a different MAC header than 802.3, however. So, to bridge the traffic, the access point simply swaps an 802.11 header for an 802.3 header, and vice versa, using the same MAC addresses. Some wireless APs route traffic from the wireless network to the wired network.
802.11 includes several standards. 802.11b transmits at 11 Mbps using the 2.4 GHz frequency band, but it is shared, with the maximum throughput capped at about 7 Mbps.
802.11a, which runs in the 5 Ghz frequency band, now can run at speeds up to 54 Mbps, as can 802.11g, which uses the 2.4 Ghz band, like 802.11b. And the latest draft 2.0 802.11n can run at the speed of 108 Mbps up to 300 Mbps with enhancement MIMO technology. Although 802.11n is still draft version but mostly all the wireless manufacturers have adopted this draft 802.11n to their line of wireless products from USB wireless adapters; PCI wireless adapters; wireless routers (such as Linksys wireless routers; D-link wireless routers or NETGEAR wireless routers and more).
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