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Introduction
Wi-Fi Technologies
Wi-Fi Architecture
Wi-Fi Network Elements
How a Wi-Fi Network Works
Wi-Fi Network Topologies
Wi-Fi Configurations
Applications of Wi-Fi

Wireless Technology is an alternative to Wired Technology,
which is commonly used, for connecting devices in wireless
mode.
Wi-Fi (Wireless Fidelity) is a generic term that refers to the
IEEE 802.11 communications standard for Wireless Local
Area Networks (WLANs).
Wi-Fi Network connect computers to each other, to the
internet and to the wired network.
Wireless Network Design
Radio Modes
Bridged Networking

ny wireless network can be thought of as a combination of one or
more of these types of connections:
2.Point-to-Point
3.Point-to-Multipoint
4.Multipoint-to-Multipoint

he simplest connection is the Point-to-Point link. These links can
be used to extend a network over great distances.

hen more than one computer communicates with a central point,
this is a Point-to-Multipoint network.

hen any node of a network may communicate with any other, this
is a multipoint-to-multipoint network(also known as an ad-hoc or
mesh network).

i-Fi cards can be operated in one of these modes:

aster(Access Point) Managed (also known as client or station)
Ad-hoc.

onitor.

ther proprietary modes(e.g. Mikrotik Nstreme).
adios may only operate in one mode at a time.


aster mode (also called AP or infrastructure mode) is used to
create a service that looks like a traditional access point.

he wireless card creates a network with a specified name (called
the SSID) and channel, and offers network services on it.

ireless cards in master mode can only communicate with cards
that are associated with it in managed mode.


anaged mode is sometimes also referred to as client mode.

ireless cards is managed mode will join a network created by a
master, and will automatically change their channel to match it.

lients using a given access point are said to be associated with
it.

anaged mode cards do not communicate with each other
directly, and will only communicate with an associated master.


d-hoc mode creates a multipoint-to-multipoint network when
there is no master or AP available.

n ad-hoc mode, each wireless card communicates directly with
its neighbors.

odes must be in range of each other to communicate, and must
agree on a network name and channel.


onitor mode is used by some tools (such as Kismet) to
passively listen to all radio traffic on a given channel.

his is useful for analyzing problems on a wireless link or
observing spectrum usage in the local area.

onitor mode is not used for normal communications.

n a simple local area wireless network, a bridged architecture is
usually adequate.
dvantages:
Very simple configuration Roaming works very well.
isadvantages:
Increasingly inefficient as nodes are added.
All broadcast traffic is repeated Virtually unusable on very
large wide-area networks.

arge networks are built by applying routing between nodes.
tatic routing is often used on point-to-point links Dynamic routing
(such as RIP or OSPF) can be used on larger networks, although
they are not designed to work with imperfect wireless links Mesh
routing Protocols (OLSR, HSLS,AODV) work very well with
wireless networks, particularly when using radios in ad-hoc
mode.

Wi-Fi Networks use Radio Technologies to transmit & receive
data at high speed:
1.IEEE 802.11b
2.IEEE 802.11a
3.IEEE 802.11g

Appear in late 1999
Operates at 2.4GHz radio spectrum
11 Mbps (theoretical speed) – within 30 m Range
4-6 Mbps (actual speed)
100 -150 feet range
Most popular, Least Expensive
Interference from mobile phones and Bluetooth devices which
can reduce the transmission speed.

Introduced in 2001
Operates at 5 GHz (less popular)
54 Mbps (theoretical speed)
15-20 Mbps (Actual speed)
50-75 feet range
More expensive
Not compatible with 802.11b

Introduced in 2003
Combine the feature of both standards (a,b)
100-150 feet range
54 Mbps Speed
2.4 GHz radio frequencies
Compatible with ‘b’

There are three sublayers in physical layer:
3.Direct Sequence Spread Spectrum (DSSS)
4.Frequency Hoping Spread Spectrum (FHSS)
5.Diffused Infrared (DFIR) – Wide angle

•Direct sequence signaling technique divides the 2.4 GHz
band into 11 22-MHz channels. Adjacent channels overlap
one another partially, with three of the 11 being completely
non-overlapping. Data is sent across one of these 22 MHz
channels without hopping to other channels.

The data link layer consists of two sublayers :
Logical Link Control (LLC)
Media Access Control (MAC).
802.11 uses the same 802.2 LLC and 48-bit addressing as
other 802 LANs, allowing for very simple bridging from
wireless to IEEE wired networks, but the MAC is unique to
WLANs.

Carrier Sense Medium Access with collision avoidance protocol
(CSMA/CA)
Listen before talking
Avoid collision by explicit Acknowledgement (ACK)
Problem: additional overhead of ACK packets, so slow
performance
Request to Send/Clear to Send (RTS/CTS) protocol
Solution for “hidden node” problem
Problem: Adds additional overhead by temporarily reserving
the medium, so used for large size packets only
retransmission would be expensive

Power Management
MAC supports power conservation to extend the battery life of portable
devices
•Power utilization modes
Continuous Aware Mode
•Radio is always on and drawing power
Power Save Polling Mode
•Radio is “dozing” with access point queuing any data for it
•The client radio will wake up periodically in time to receive
regular beacon signals from the access point.
•The beacon includes information regarding which stations have
traffic waiting for them
•The client awake on beacon notification and receive its data

Fragmentation
CRC checksum
Each pocket has a CRC checksum calculated and attached
to ensure that the data was not corrupted in transit
Association & Roaming

Access Point (AP) – The AP is a wireless LAN transceiver or “base
station” that can connect one or many wireless devices
simultaneously to the Internet.
Wi-Fi cards – They accept the wireless signal and relay
information. They can be internal and external.(e.g. PCMCIA
Card for Laptop and PCI Card for Desktop PC)
Safeguards – Firewalls and anti-virus software protect networks
from uninvited users and keep information secure.

•Basic concept is same as Walkie talkies.
•A Wi-Fi hotspot is created by installing an access point to an
internet connection.
•An access point acts as a base station.
•When Wi-Fi enabled device encounters a hotspot the device
can then connect to that network wirelessly.
•A single access point can support up to 30 users and can
function within a range of 100 – 150 feet indoors and up to
300 feet outdoors.
•Many access points can be connected to each other via
Ethernet cables to create a single large network.

pAP-based topology (Infrastructure Mode)
yPeer-to-peer topology (Ad-hoc Mode)
oPoint-to-multipoint bridge topology

The client communicate through Access Point.
BSA-RF coverage provided by an AP.
ESA-It consists of 2 or more BSA.
ESA cell includes 10-15% overlap to allow roaming.

AP is not required.
Client devices within a cell
can communicate directly
with each other.
It is useful for setting up of a
wireless network quickly and
easily.

This is used to connect a LAN in one building to a LANs in
other buildings even if the buildings are miles apart. These
conditions receive a clear line of sight between buildings.
The line-of-sight range varies based on the type of wireless
bridge and antenna used as well as the environmental
conditions.

Home
Small Businesses or SOHO
Large Corporations & Campuses
Health Care
Wireless ISP (WISP)
Travellers

Thank You