The IEEE 802.11 standards specify two operating modes: infrastructure mode and ad hoc mode.
Infrastructure mode is used to connect computers with wireless network adapters to an existing wired network with the help from wireless router or access point, while Ad hoc mode is used to connect wireless clients directly together, without the need for a wireless router or access point.
The 802.11 standard establishes and defines the mode of channelling the unlicensed radio frequency bands in WLANs. The 2.4 GHz band is broken down into 11 channels for North America and 13 channels for Europe. These channels have a centre frequency separation of only 5 MHz and an overall channel bandwidth (or frequency occupation) of 22 MHz.
The IEEE 802.11a adopted the OFDM modulation technique and uses the 5 GHz band.
The 802.11a devices operating in the 5 GHz band are less likely to experience interference than devices that operate in the 2.4 GHz band because there are fewer consumer devices that use the 5 GHz band. Also, higher frequencies allow for the use of smaller antennas.
Speed: Uses up to Up to 54 Mbps
a. Has the fastest transmission speed.
b. Allows for more simultaneous users.
c. Uses the 5 GHz frequency, which limits interference from other devices.
Few disadvantages of using the 5 GHz band are;
a. Higher frequency radio waves are more easily absorbed by obstacles such as walls, making 802.11a susceptible to poor performance due to obstructions.
b. Higher frequency band has slightly poorer range than either 802.11b or g. Also, some countries, including Russia, do not permit the use of the 5 GHz band, which may continue to curtail its deployment.
c. Is not compatible with 802.11b network adapters, routers, and access points.
This was the first and, until recently, the most common wireless variant used. With transmission speeds of just 11Mbits/sec it is also the slowest. It also used the 40bit Wireless Equivalency Privacy (WEP) security protocol, which
was found to have a number of deficiencies. A newer version of this, 802.11b+ maintains speeds to 22Mbits/sec.
Speed : 11megabits per seconds
Has the best signal range.
Transmission speed is slow
Uses the 2.4 gigahertz (GHz) of frequency the same as some house hold items like cordless, micro waves ovens etc.
Provides access to few users simultaneously.
This is the most recent and popular in use now, offering more respectable data transfer speeds of up to 54Mbits/sec, but its speed are much lower. It also uses an upgraded form of Wi-Fi Protected Access (WPA) security protocol.
Speed: Uses Up to 54 Mbps
Has a transmission speed comparable to 802.11a under optimal conditions
a. Allows for more simultaneous users
b. Has the best signal range and is not easily obstructed
c. Is compatible with 802.11b network adapters, routers, and access points
Uses the 2.4 GHz frequency so it has the same interference problems as 802.11b
Costs more than 802.11b
The 802.11n draft standard is intended to improve wireless data rates and range without requiring additional power or radio frequency band allocation. The 802.11n uses multiple radios and antennae at endpoints, each broadcasting on the same frequency to establish multiple streams. The multiple input/multiple output technology splits a high data-rate stream into multiple lower rate streams and broadcasts them at the same time over the available radios and antennae. This allows for a speculative maximum data rate of 248 Mb/s using two streams.
If your PC or laptop have more than one wireless network adapter or your adapter uses more than one wireless technology / standard, you are provided with options to specify which adapter or standard to use for each network connection.
E.g., if you use streaming media, such as videos or music, on your PC or Laptop, choosing 802.11a connection from the options provided would be best for you, because you will get a faster data transfer rate when you watch videos or listen to music.