A local area network (LAN) is a computer network covering a small local area, like a home, office, or small group of buildings such as a home, office, or college. Current LANs are most likely to be based on switched Ethernet or Wi-Fi technology running at 10, 100 or 1,000 Mbit/s (1,000 Mbit/s is also known as 1 Gbit/s).
The defining characteristics of LANs in contrast to WANs are: a) much higher data rates, b) smaller geographic range - at most a few kilometers - and c) they do not involve leased telecommunication lines. "LAN" usually does not refer to data running over local analog telephone lines, as on a private branch exchange (PBX).
A Local Area Network (LAN) allows computing equipment to share information from any device on a network with other devices on the same network, and includes cabling, network transmission devices, network interfaces, and computing devices. Some examples of computing devices on a LAN include:
File Servers--Computers which "serve" as central storage facilities for data and program files.
Print Servers--Computers with one or more printers attached that provide printing "services" to other computers on the LAN. Some printers have special interfaces which allow the printer itself to act as a print server on a network.
Modem/Fax/Communications Servers--Devices which allow computers on the LAN to communicate outside the network through a standard local telephone system. It is also possible, with appropriate communications servers and software, to allow external computers to "dial-in" to a LAN and communicate (data and/or faxes) with devices on the LAN.
A wireless LAN or WLAN is a wireless local area network that uses radio waves as its carrier: the last link with the users is wireless, to give a network connection to all users in the surrounding area. Areas may range from a single room to an entire campus. The backbone network usually uses cables, with one or more wireless access points connecting the wireless users to the wired network.
Method of Communication
A Wireless LAN is a wireless network using radio frequencies for communication between computer devices. The frequency that a particular device transmits on or receives from is designated in two ways: standard and channel.
Standard
In 1990, the IEEE (Institute of Electrical and Electronic Engineers) formed a group to develop a standard for wireless equipment. On June 26, 1997, a standard was finally developed called 802.11. The standard specified that the upper layers of the OSI model can not be modified, and WLANs must be implemented on the physical and data link layers. This provided the ability to run any operating system or LAN application on a WLAN without any modification. They accomplished this by doing upper layer features on the data link layer.
B
The original 802.11 standard limited WLAN speed to 2 Mbit/s, which is not efficient enough for most networking needs. In September of 1999, 802.11b was amended to the original standard. The B standard offered two higher speeds, 5.5 Mbit/s and 11 Mbit/s, to the original 1 or 2 Mbit/s standard.
A
At the same time 802.11b was released, 802.11a was also added to the 802.11 standard. 802.11a has a maximum speed of 54 Mbit/s and supports speeds of 48, 36, 24, 18, 12, 9, and 6 Mbit/s at a frequency of 5 GHz. 802.11a maintains the same 802.11b MAC layer functions, but they are different in the way they operate at the physical layer. The reason that 802.11a is faster than 802.11b is because of a more sophisticated modulation and an efficient error-checking scheme. While 802.11a and 802.11b were released at the same time, 802.11a wasn't implemented until late in 2001. 802.11a was pushed back due to the backward compatibility with widely deployed 802.11b network and higher cost of implementation. The reason that 802.11a is more expensive is because of the wider available spectrum in the 5GHz band (from 100 to 900MHz depends on country) than 2.4GHz (83.5MHz).
G
The IEEE then revisited the 802.11 standard one last time to combine the best of both worlds. The new standard would keep the stable and accepted features of 802.11b, and increase the data speed standards so that they are comparable with 802.11a. In late 2001, a draft was proposed called 802.11g. 802.11g runs on the same RF band as B (2.4 GHz) but uses the transmission techniques of A. Like A, the G standard also permits vendors to incorporate proprietary techniques that can potentially push the speeds of G to 108 Mbit/s.
Modes of operation
Peer-to-peer or ad-hoc mode
This mode is a method for wireless devices to directly communicate with each other. Operating in ad-hoc mode allows wireless devices within range of each other to discover and communicate in peer-to-peer fashion without involving central access points.
This is typically used by two PCs to connect to one another, so that one can share the other's Internet connection for example, as well as for wireless mesh networks.
If you have a strength meter for the signal coming from all the other ad-hoc devices the meter will not read the strength accurately, and can be misleading, because it is registering the strength of the strongest signal, such as the closest computer.
Access Point / Client
The most common is to have access points wired to Internet, and then having wireless clients (typically laptops) accessing Internet through the access point.
Almost any computer with a wireless card and wired connection to Internet can be set up as an Access Point, but today one can buy dedicated boxes cheaply. Those boxes usually look like a hub or router with antenna, bridges a wireless network to a wired Ethernet network. Administration of the access point (like setting SSID, putting up encryption, etc) is usually done through a web interface or telnet.
Home networks would typically have a stand-alone access point wired up i.e. through an ADSL connection, while hotspots and professional networks (i.e. providing wireless coverage in an office building) typically would have multiple access points, placed at strategical points.
Wireless distribution system
When it's difficult to get all the Access Points wired up, it's also possible to put up access points as repeaters.
Monitoring station
Some wireless network cards can be set up to monitor a network without connecting to an access point or revealing itself. This can be used to sniff clear-text activity, or to crack encryption.
Components of a Wireless LAN
Access Point(AP)
Access points are two-way transceivers that broadcast data into the surrounding environment.
Wireless Capture Device
Wireless devices are peripherals designed for personal computers. Their purpose is to allow the computer - and therefore its user - to connect to a network through radio waves. These peripherals can be found as PCI cards, or portable USB devices. When activated, they scan their environment for signals from a wireless access point. If one is found, they allow the user to connect to the access point. The wireless capture card can determine if the access point is secured with an encryption method (usually WEP or WPA) and can still allow the user to connect to it assuming the key or passcode is available.