INTRODUCTION TO WIFI
Wi-Fi was developed to be used for mobile computing
devices such as laptops, internet VoIP phone access,
gaming and basic connectivity of consumer electronics
such as television and DVD players or even digital
cameras. A person with a Wi-Fi enabled device such as
a computer, cellphone or PDA can connect to the
Internet when in proximity of an access point. The
region covered by one or several access points is
called a hotspot. Hotspots can range from a single
room to many square miles of overlapping hotspots.
The 802.11 amendment attempts to define the two lower
layers of the seven-layer ISO for a wireless
connection through electromagnetic waves, which means
:
- the physical layer (also called PHY), proposes
three types of information coding
- the data link layer has two sub-layers named
Logical Link Control (LLC) and the Media Access
Control (MAC)
The shapes of the electrical connectors, which
frequencies they broadcast on, what modulation scheme
to use and similar low-level things are specified in
the physical layer, in comparison to the data link
layer which provides the functional and procedural
means to transfer data between network entities and
might provide the means to detect and possibly
correct errors that may occur in the Physical layer.
The 802.11 amendment proposes 3 physical layers to
define different means of transmission :
It is possible to use any type of high level protocol
on a WiFi wireless network the same way you would
with an ethernet connection.
Different WiFi standards
802.11 is a set of IEEE Data Link
Layer amendments that govern wireless networking
transmission methods. They are commonly used today in
their 802.11a, 802.11b, and 802.11g versions to
provide wireless connectivity in the home, office and
some commercial establishments.
The 802.11a amendment (baptized WiFi
5) allows users to have a maximum raw data rate of 54
Mbit/s, which yields a net throughput in the mid-30
Mbit/s. The 802.11a amendment has 8 radio channels at
a 5GHz frequency.
The 802.11b is the most commonly
used amendment nowadays. It has a maximum raw data
rate of 11 Mbit/s. In practice the maximum 802.11b
throughput that an application can achieve is about
5.9 Mbit/s. Typical range can vary up to 300 meters
in an open area. The frequency runs at 2.4 GHz, with
3 available radio channels.
The public has no interest in the 802.11
c amendment. It's only a modification to the
802.11 d amendment. It was created to be able to make
a link between the 802.11 trams (data link level)
Going global
The 802.11d amendment is a wireless
network communications specification for use in
countries where systems using other standards in the
802.11 family are not allowed to operate. The
amendment eliminates the need for designing and
manufacturing dozens of different hardware solutions,
each for use in a particular jurisdiction.
The 802.11e amendment offers quality
of service (QoS) features, including the
prioritization of data, voice, and video
transmissions. It provides seamless interoperability
between business, home, and public environments such
as airports and hotels, and is especially well suited
for use in networks that include multimedia
capability.
The 802.11f amendment is a proposal
that describes wireless access-point communications
among multivendor systems. This technology, to be
specified as the Inter-Access Point Protocol, handles
the registration of APs within a network and the
exchange of information when a user is roaming among
coverage areas supported by different vendors' access
points. It will help with fast hand-off from AP to
AP.
The 802.11g amendment is a standard
for wireless local area networks (WLANs) that offers
transmission over relatively short distances at up to
54 megabits per second (Mbps), compared with the 11
Mbps theoretical maximum with the earlier 802.11b
amendment. Networks employing 802.11g operate at
radio frequencies which range between 2.400 GHz and
2.4835 GHz, the same band as 802.11b.
802.11 h is intended to resolve
interference issues introduced by the use of 802.11a
in some locations, particularly with military radar
systems and medical devices.
802.11 i is a standard for wireless
local area networks (WLANs) that provides improved
encryption for networks that use the 802.11a, 802.11b
(which includes Wi-Fi) and the 802.11g amendment. The
802.11i standard requires new encryption key
protocols, known as Temporal Key Integrity Protocol
(TKIP) and Advanced Encryption Standard (AES). The
802.11i standard was officially ratified by the IEEE
in June of 2004, and thereby became part of the
802.11 family of wireless network specifications.
The 802.11 r standard is designed to
speed handoffs between access points or cells in a
wireless LAN.
The 802.11 j specification is a
proposed addition to the 802.11 family of amendments
for wireless local area networks (WLANs) that
incorporates Japanese regulatory extensions to the
802.11a amendment. It is interesting to note the
existence of another standard nammed <<802.11
b+>>. This is a proprietary standard that
proposes amelioration through the output frequencies.
In return this standard suffers from gaps in terms of
interoperability guarantee as it is not an IEEE
standard.
Ranges and Outputs
The 802.11a, 802.11b and 802.11g are
all physical standards. They correspond to a revision
of the 802.11 standard. It proposes multiple
executions that allow for different data rates
(debits) in function with their range.
802.11 a
The 802.11a standard uses the same core protocol as
the original standard, operates in 5 GHz band, and
uses a 52-subcarrier orthogonal frequency-division
multiplexing (OFDM) with a maximum raw data rate of
54 Mbit/s, which is 5 times more than the 802.11b,
for a range of approximately 30 feet.It uses 8
channels that cannot be masked.
802.11b
The 802.11b amendment allows for a raw data rate of
11 Mbps, and can reach up to 50 meters internally and
up to 200 meters outdoors (even above that if there
are directional antennas).
802.11g
The 802.11g amendment allows a 54 Mbps raw data rate
with a range equivalent to the 802.11b. On the other
hand if the 802.11g amendment uses the 2,4 GHZ
frequency with a OFDM code, this amendment is
compatible with 802.11b equipments with the exception
of certain old equipments.