Introduction to Wi-Fi (802.11 or WiFi)

The IEEE 802.11 specification (ISO/IEC 8802-11) is an international standard describing the characteristics of a wireless local area network (WLAN). The name Wi-Fi (which stands for Wireless Fidelity, sometimes incorrectly shortened to WiFi) corresponds to the name of the certification given by the Wi-Fi Alliance, formerly WECA (Wireless Ethernet Compatibility Alliance). This group ensures compatibility between hardware devices that use the 802.11 standards. Read on to learn more.

Coverage

Hardware devices certified by the Wi-Fi Alliance are allowed to use this logo:

With Wi-Fi, it is possible to create high-speed wireless local area networks if the computer to be connected is not too far from the access point. In practice, Wi-Fi can be used to provide high-speed connections (11 Mbps or greater) to laptop computers, desktop computers, PDAs and any other devices located within a radius of several dozen meters (around 39ft.) indoors (in general 20m-50m/60ft.-164ft. away) or within several hundred metres/ft. outdoors.

Wi-Fi providers are starting to blanket areas with a high concentration of users (like train stations, airports, and hotels) with wireless networks. These access areas are called hot spots.

Introduction to Wi-Fi (802.11)

The 802.11 standard reserves the low levels of the OSI model for a wireless connection that uses electromagnetic waves, that is:

The physical layer: sometimes shortened to the "PHY" layer, it offers three types of information encoding.
The data link layer comprises two sub-layers: Logical Link Control (or LLC) and Media Access Control (or MAC).

The physical layer defines the radio wave modulation and signaling characteristics for data transmission. In contrast, the data link layer defines the interface between the machine's bus and the physical layer, particularly an access method close to the one used in the Ethernet standard and rules for communication between the network stations. The 802.11 standard has three physical layers that define alternative modes of transmission:

Data Link Layer (MAC)

802.2

802.11

Physical Layer (PHY)

DSSS

FHSS

Infrared

Any high-level protocol can be used on a Wi-Fi wireless network the same way it can be used on an Ethernet network.

The Different WiFi Standards

The IEEE 802.11 standard is only the earliest standard, allowing 1-2 Mbps of bandwidth. Amendments have to be made to the original standard in order to optimize bandwidth (these include the 802.11a, 802.11b and 802.11g standards, which are called 802.11 physical standards) or to better specify components in order to ensure improved security or compatibility. This table shows the various amendments to the 802.11 standard and their significance:

Name of standard	Name	Description
802.11a	Wifi5	The 802.11a standard (called WiFi 5) allows higher bandwidth (54 Mbps maximum throughput, 30 Mbps in practice). The 802.11a standard provides 8 radio channels in the 5 GHz frequency band.
802.11b	WiFi	The 802.11b standard is currently the most widely used one. It offers a maximum thoroughput of 11 Mbps (6 Mbps in practice) and a reach of up to 300 metres in an open environment. It uses the 2.4 GHz frequency range, with 3 radio channels available.
802.11c	Bridging 802.11 and 802.1d	The 802.11c bridging standard is of no interest to the general public. It is only an amended version of the 802.1d standard that lets 802.1d bridge with 802.11-compatible devices (on the data link level).
802.11d	Internationalization	The 802.11d standard is a supplement to the 802.11 standard which is meant to allow international use of local 802.11 networks. It lets different devices trade information on frequency ranges depending on what is permitted in the country where the device is from.
802.11e	Improving service quality	The 802.11e standard is meant to improve the quality of service at the level of the data link layer. The standard's goal is to define the requirements of different packets in terms of bandwidth and transmission delay so as to allow better transmission of voice and video.
802.11f	Roaming	The 802.11f is a recommendation for access point vendors that allows products to be more compatible. It uses the Inter-Access Point Roaming Protocol, which lets a roaming user transparently switch from one access point to another while moving around, no matter what brands of access points are used on the network infrastructure. This ability is also simply called roaming.
802.11g		The 802.11g standard offers high bandwidth (54 Mbps maximum throughput, 30 Mbps in practice) on the 2.4 GHz frequency range. The 802.11g standard is backwards-compatible with the 802.11b standard, meaning that devices that support the 802.11g standard can also work with 802.11b.
802.11h		The 802.11h standard is intended to bring together the 802.11 standard and the European standard (HiperLAN 2, hence the h in 802.11h) while conforming to European regulations related to frequency use and energy efficiency.
802.11i		The 802.11i standard is meant to improve the security of data transfers (by managing and distributing keys, and implementing encryption and authentication). This standard is based on the AES (Advanced Encryption Standard) and can encrypt transmissions that run on 802.11a, 802.11b and 802.11g technologies.
802.11Ir		The 802.11r standard has been elaborated so that it may use infra-red signals. This standard has become technologically obsolete.
802.11j		The 802.11j standard is to Japanese regulation what the 802.11h is to European regulation.

It is also helpful to note the existence of a standard called "802.11b+". This is a proprietary standard with improvements in the data flow. However, this standard also suffers from gaps in interoperability due to not being an IEEE standard.

Range and data flow

The 802.11a, 802.11b, and 802.11g standards, called physical standards, are amendments to the 802.11 standards and offer different modes of operation that allows them to reach different data transfer speeds depending on their range.

Standard	Frequency	Speed	Range
WiFi a (802.11a)	5 GHz	54 Mbit/s	10 m
WiFi B (802.11b)	2.4 GHz	11 Mbit/s	100 m
WiFi G (802.11b)	2.4 GHz	54 Mbit/s	100 m

802.11a

The 802.11 standard has a maximum theoretical data flow of 54 Mbps, five times that of 802.11b, but at a range of only about thirty meters/ninety-eight feet. The 802.11a standard relies on OFDM (Orthogonal Frequency Division Multiplexing) technology. It broadcasts in the 5 GHz frequency range and uses 8 non-overlapping channels.

Because of this, 802.11a devices are incompatible with 802.11b devices. However, some devices incorporate both 802.11a and 802.11b chips, called dual-band devices.

Hypothetical speed (indoors)	Range
54 Mbits/s	10 m
48 Mbits/s	17 m
36 Mbits/s	25 m
24 Mbits/s	30 m
12 Mbits/s	50 m
6 Mbits/s	70 m

802.11b

The 802.11b standard allows for a maximum data transfer speed of 11 Mbps, at about 100 meters/328 ft. indoors and up to 200 meters/656 ft. outdoors (or even beyond that, with directional antennas.)

Hypothetical speed	Range (indoors)	Range (outdoors)
11 Mbits/s	50 m	200 m
5.5 Mbits/s	75 m	300 m
2 Mbits/s	100 m	400 m
1 Mbit/s	150 m	500 m

802.11g

The 802.11g standard allows for a maximum data transfer speed of 54 Mbps at ranges comparable to the 802.11b standard. What's more, as the 802.11g standard uses the 2.4GHz frequency range with OFDM coding, this standard is compatible with 802.11b devices, except for some older devices.