Introduction to Wi-Fi (802.11 or WiFi)

Introduction to Wi-Fi (802.11 or WiFi)
Introduction to Wi-Fi (802.11)
The IEEE 802.11 specification (ISO/IEC 8802-11) is an international standard
describing the characteristics of a wireless local area network (WLAN). The nameWiFi (short 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), the group which ensures compatibility between
hardware devices that use the 802.11 standard. Today, due to misuse of the terms
(and for marketing purposes), the name of the standard is often confused with the
name of the certification. A Wi-Fi network, in reality, is a network that complies with
the 802.11 standard. 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, provided
that the computer to be connected is not too far from the access point. In practice, WiFi can be used to provide high-speed connections (11 Mbps or greater) to laptop
computers, desktop computers, personal digital assistants(PDAs) and any other devices
located within a radius of several dozen metres indoors (in general 20m-50m away) or
within several hundred metres outdoors.
Wi-Fi providers are starting to blanket areas that have 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, i.e.:

The physical layer (sometimes shortened to the "PHY" layer), which offers three types
of information encoding.

The data link layer, comprised of two sub-layers: Logical Link Control (orLLC)
and Media Access Control (or MAC).
The physical layer defines the radio wave modulation and signalling characteristics for
data transmission, while the data link layer defines the interface between the machine's
bus and the physical layer, in particular an access method close to the one used in
the Ethernet standard and rules for communication between the stations of the
network. The 802.11 standard actually has three physical layers, which define
alternative modes of transmission:
Data Link Layer 802.2
(MAC)
Physical
802.11
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 various Wi-Fi standards
The IEEE 802.11 standard is actually only the earliest standard, allowing 1-2 Mbps of
bandwidth. Amendments have 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
The 802.11a standard (called WiFi 5) allows
higher
802.11a
Wifi5
bandwidth
(54
Mbps
maximum
throughput, 30 Mbps in practice). The
802.11a standard provides 8 radio channels
in the 5 GHz frequency band.
The 802.11b standard is currently the most
widely used one. It offers a maximum
thoroughput of 11 Mbps (6 Mbps in
802.11b
WiFi
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.
The 802.11c bridging standard is of no
802.11c
Bridging
and 802.1d
802.11
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).
The 802.11d standard is a supplement to
the 802.11 standard which is meant to
allow international use of local 802.11
802.11d
Internationalization networks. It lets different devices trade
information on frequency ranges depending
on what is permitted in the country where
the device is from.
The 802.11e standard is meant to improve
the quality of service at the level of the data
802.11e
Improving
quality
service
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.
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
802.11f
Roaming
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.
The
802.11g
standard
offers
high
bandwidth (54 Mbps maximum throughput,
30 Mbps in practice) on the 2.4 GHz
802.11g
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.
The 802.11h standard is intended to bring
802.11h
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.
The 802.11i standard is meant to improve
the security of data transfers (by managing
and distributing keys, and implementing
802.11i
encryption
and
authentication).
This
standard is based on the AES (Advanced
Encryption
Standard)
transmissions
that
and
run
can
on
encrypt
802.11a,
802.11b and 802.11g technologies.
The 802.11r stadard has been elaborated
802.11Ir
so that it may use infra-red signals. This
standard
has
become
technologically
obsolete.
The 802.11j standard
802.11j
is
to
Japanese
regulation what the 802.11h is to European
regulation.
It is also useful to note the existence of a standard called "802.11b+". This is a
proprietary standard with improvements in 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 standard and offer different modes of operation, which lets
them 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 metres. The 802.11a standard relies on
a technology called OFDM (Orthogonal Frequency Division Multiplexing). 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,
there are devices that 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 a
range of about 100 m indoors and up to 200 metres outdoors (or even beyond that,
with directional antennas.)
Hypothetical speed
Range
Range
(indoors) (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 those of 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, with the exception of some older devices.
Hypothetical speed
Range
Range
(indoors) (outdoors)
54 Mbits/s
27 m
75 m
48 Mbits/s
29 m
100 m
36 Mbits/s
30 m
120 m
24 Mbit/s
42 m
140 m
18 Mbit/s
55 m
180 m
12 Mbit/s
64 m
250 m
9 Mbit/s
75 m
350 m
6 Mbit/s
90 m
400 m
Source: http://en.kioskea.net/contents/802-introduction-to-wi-fi-802-11-or-wifi
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