Transcript The Freedom of Wi-Fi

WI-FI TECHNOLOGY
By.
P. Victer Paul
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AGENDA
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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
INTRODUCTION
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Wireless Technology is an alternative to Wired Technology,
which is commonly used, for connecting devices in wireless
mode.
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Wi-Fi (Wireless Fidelity) is a generic term that refers to the
IEEE 802.11 communications standard for Wireless Local
Area Networks (WLANs).
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Wi-Fi Network connect computers to each other, to the
internet and to the wired network.
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Wireless Network Design
Radio Modes
Bridged Networking
WIRELESS NETWORK DESIGN
Any wireless network can be thought of as a combination of one
or more of these types of connections:
1.
2.
3.
Point-to-Point
Point-to-Multipoint
Multipoint-to-Multipoint
POINT TO POINT
The simplest connection is the Point-to-Point link. These links can
be used to extend a network over great distances.
POINT TO MULTIPOINT
When more than one computer communicates with a central
point, this is a Point-to-Multipoint network.
MULTIPOINT TO MULTIPOINT
When 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).
RADIO MODES
Wi-Fi cards can be operated in one of these modes:
Master(Access Point) Managed(also known as client or station)
Ad-hoc.
 Monitor.
 Other proprietary modes(e.g. Mikrotik Nstreme).
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Radios may only operate in one mode at a time.
MASTER MODE
Master mode (also called AP or infrastructure mode) is used to
create a service that looks like a traditional access point.
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The wireless card creates a network with a specified name
(called the SSID) and channel, and offers network services on it.
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Wireless cards in master mode can only communicate with
cards that are associated with it in managed mode.
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MANAGED MODE
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Managed mode is sometimes also referred to as client mode.
Wireless cards is managed mode will join a network created by
a master, and will automatically change their channel to match
it.
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Clients using a given access point are said to be associated
with it.
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Managed mode cards do not communicate with each other
directly, and will only communicate with an associated master.
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AD-HOC MODE
Ad-hoc mode creates a multipoint-to-multipoint network when
there is no master or AP available.
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In ad-hoc mode, each wireless card communicates directly
with its neighbors.
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Nodes must be in range of each other to communicate, and
must agree on a network name and channel.
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MONITOR MODE
Monitor mode is used by some tools (such as Kismet) to
passively listen to all radio traffic on a given channel.
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This is useful for analyzing problems on a wireless link or
observing spectrum usage in the local area.
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Monitor mode is not used for normal communications.
BRIDGED NETWORKING
In a simple local area wireless network, a bridged architecture is
usually adequate.
Advantages:
Very simple configuration Roaming works very well.
Disadvantages:
Increasingly inefficient as nodes are added.
All broadcast traffic is repeated Virtually unusable on very
large wide-area networks.
ROUTED NETWORKING
Large networks are built by applying routing between nodes.
Static 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.
THE WI-FI TECHNOLOGY
Wi-Fi Networks use Radio Technologies to transmit & receive
data at high speed:
1.
2.
3.
IEEE 802.11b
IEEE 802.11a
IEEE 802.11g
IEEE 802.11B
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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.
IEEE 802.11A
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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
IEEE 802.11G
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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’
802.11 PHYSICAL LAYER
There are three sublayers in physical layer:
1.
2.
3.
Direct Sequence Spread Spectrum (DSSS)
Frequency Hoping Spread Spectrum (FHSS)
Diffused Infrared (DFIR) - Wide angle
DSSS
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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.
IEEE 802.11 DATA LINK LAYER
The data link layer consists of two sublayers :
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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.
802.11 MEDIA ACCESS CONTROL
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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
802.11 MEDIA ACCESS CONTROL(CONT.)
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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
802.11 MEDIA ACCESS CONTROL(CONT.)
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Fragmentation
CRC checksum
 Each pocket has a CRC checksum calculated and attached
to ensure that the data was not corrupted in transit
Association & Roaming
ELEMENTS OF A WI-FI NETWORK
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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.
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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)
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Safeguards - Firewalls and anti-virus software protect networks
from uninvited users and keep information secure.
HOW A WI-FI NETWORK WORKS
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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.
WI-FI NETWORK TOPOLOGIES
1.
AP-based topology (Infrastructure Mode)
2.
Peer-to-peer topology (Ad-hoc Mode)
3.
Point-to-multipoint bridge topology
AP-BASED TOPOLOGY
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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.
PEER-TO-PEER TOPOLOGY
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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.
POINT-TO-MULTIPOINT BRIDGE TOPOLOGY
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.
WI-FI CONFIGURATIONS
WI-FI CONFIGURATIONS
WI-FI CONFIGURATIONS
WI-FI APPLICATIONS
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Home
Small Businesses or SOHO
Large Corporations & Campuses
Health Care
Wireless ISP (WISP)
Travellers
Thank You