A wireless LAN (WLAN) is a set of network components connected by electromagnetic (radio) waves instead of wires. WLANs are used in combination with or as a substitute to wired computer networks, adding flexibility and freedom of movement within the workplace. Wireless LAN clients enjoy great mobility and can access information on the company network or even the Internet from the store, boardroom or throughout the campus without relying on the availability of wired cables and connections.
The proposed standard 802.11 works in two modes:
1. In the presence of base station.
2. In the absence of base station
In first case all communication goes through the base station known as the access point in 802.11 terminologies .This is known as infrastructure mode. In latter case, the computers just communicate with each other directly this mode is called as ad hoc networking.
IEEE 802.11 denotes set of wireless LAN/WLAN standards developed by IEEE standards working committee (IEEE 802). Some of the many challenges that had to be met where :finding a suitable frequency band that was available, preferably worldwide; dealing with the fact that radio signals have a finite range; ensuring users privacy and security; worrying about human safety; and finally , building a system with enough bandwidth to be economically feasible.
At the time of standardization process it was decided that 802.11 be made compatible with Ethernet above data link layer. But several inherent differences exist and had to be dealt with by the standard.
First, a computer on Ethernet always listens to the ether before transmitting .In case of wireless LANs this is not possible. It may happen that the range of a station may not be able to detect the transmission taking place between other two stations resulting in collision.
The second problem that had to be solved is that radio signals can be reflected off the solid objects, so it may be received multiple times. This interference results in Multipath fading.
The third problem is that if a notebook computer is moved away from base station to another there must be some way of handing it off.
After some work the committee came up with a standard that addressed these and other concerns. The most popular amendments are 802.11a, 802.11b and 802.11g to original standard. The security was also enhanced by amendment 802.11i.The other specifications from (c-f, h, j) are service enhancements and extensions
The proposed standard 802.11 works in two modes:
1. In the presence of base station.
2. In the absence of base station
In first case all communication goes through the base station known as the access point in 802.11 terminologies .This is known as infrastructure mode. In latter case, the computers just communicate with each other directly this mode is called as ad hoc networking.
IEEE 802.11 denotes set of wireless LAN/WLAN standards developed by IEEE standards working committee (IEEE 802). Some of the many challenges that had to be met where :finding a suitable frequency band that was available, preferably worldwide; dealing with the fact that radio signals have a finite range; ensuring users privacy and security; worrying about human safety; and finally , building a system with enough bandwidth to be economically feasible.
At the time of standardization process it was decided that 802.11 be made compatible with Ethernet above data link layer. But several inherent differences exist and had to be dealt with by the standard.
First, a computer on Ethernet always listens to the ether before transmitting .In case of wireless LANs this is not possible. It may happen that the range of a station may not be able to detect the transmission taking place between other two stations resulting in collision.
The second problem that had to be solved is that radio signals can be reflected off the solid objects, so it may be received multiple times. This interference results in Multipath fading.
The third problem is that if a notebook computer is moved away from base station to another there must be some way of handing it off.
After some work the committee came up with a standard that addressed these and other concerns. The most popular amendments are 802.11a, 802.11b and 802.11g to original standard. The security was also enhanced by amendment 802.11i.The other specifications from (c-f, h, j) are service enhancements and extensions
What's in a name?
ReplyDeleteYou may be wondering why people refer to WiFi as 802.11 networking. The 802.11 designation comes from the IEEE. The IEEE sets standards for a range of technological protocols, and it uses a numbering system to classify these standards.
A wireless network uses radio waves, just like cell phones, televisions and radios do. In fact, communication across a wireless network is a lot like two-way radio communication. Here's what happens:
1. A computer's wireless adapter translates data into a radio signal and transmits it using an antenna.
2. A wireless router receives the signal and decodes it. The router sends the information to the Internet using a physical, wired Ethernet connection.
The process also works in reverse, with the router receiving information from the Internet, translating it into a radio signal and sending it to the computer's wireless adapter.
The radios used for WiFi communication are very similar to the radios used for walkie-talkies, cell phones and other devices. They can transmit and receive radio waves, and they can convert 1s and 0s into radio waves and convert the radio waves back into 1s and 0s. But WiFi radios have a few notable differences from other radios:
They transmit at frequencies of 2.4 GHz or 5 GHz. This frequency is considerably higher than the frequencies used for cell phones, walkie-talkies and televisions. The higher frequency allows the signal to carry more data.
They use 802.11 networking standards, which come in several flavors:
802.11a transmits at 5 GHz and can move up to 54 megabits of data per second. It also uses orthogonal frequency-division multiplexing (OFDM), a more efficient coding technique that splits that radio signal into several sub-signals before they reach a receiver. This greatly reduces interference.
802.11b is the slowest and least expensive standard. For a while, its cost made it popular, but now it's becoming less common as faster standards become less expensive. 802.11b transmits in the 2.4 GHz frequency band of the radio spectrum. It can handle up to 11 megabits of data per second, and it uses complementary code keying (CCK) modulation to improve speeds.
802.11g transmits at 2.4 GHz like 802.11b, but it's a lot faster -- it can handle up to 54 megabits of data per second. 802.11g is faster because it uses the same OFDM coding as 802.11a.
802.11n is the newest standard that is widely available. This standard significantly improves speed and range. For instance, although 802.11g theoretically moves 54 megabits of data per second, it only achieves real-world speeds of about 24 megabits of data per second because of network congestion. 802.11n, however, reportedly can achieve speeds as high as 140 megabits per second. The standard is currently in draft form -- the Institute of Electrical and Electronics Engineers (IEEE) plans to formally ratify 802.11n by the end of 2009.
Other 802.11 standards focus on specific applications of wireless networks, like wide area networks (WANs) inside vehicles or technology that lets you move from one wireless network to another seamlessly.
WiFi radios can transmit on any of three frequency bands. Or, they can "frequency hop" rapidly between the different bands. Frequency hopping helps reduce interference and lets multiple devices use the same wireless connection simultaneously