Download - WLAN Fundamentals
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WLAN FundamentalsNirav dsouza 6002Siddharth suttraway 6042
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What is a Wireless LAN
A wireless local area network(LAN) is a flexible data communicationssystem implemented as an extension to, or as an alternative for, awired LAN.
Using radio frequency (RF) technology, wireless LANs transmit and receivedata over the air, minimizing the need for wired connections.
Thus, combining data connectivity with user mobility.
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Disadvantages of Using a
Wireless LAN and its
Practical Uses
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Benefits of Wireless LAN
Productivity, convenience, and cost advantages
Installation speed and simplicity.
Installation flexibility.
Reduced cost-of-ownership.
Mobility.
Scalability.
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Benefits of Wireless LAN
Installation speed and simplicity
No cable to pull.
Eliminates current architecture obstacles.
Few transmitters/receivers for multiple for users.
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Benefits of Wireless LAN
Installation flexibility
The network goes where wires cannot.
Not constrained by expensive walls.
Easy to add more computers and devices.
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Benefits of Wireless LAN
Reduced cost-of-ownership
Mobile devices are less expensive than computer workstations.
Can Run Errands and stay in touch.
No need to build wiring closets.
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Benefits of Wireless LAN
Mobility
Access to real-time information.
Supports productivity.
Provides service opportunities.
Promotes flexibility.
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Benefits of Wireless LAN
Scalability
Spans a variety of topologies.
Configurations are easily changed.
Works over great distances.
Effective for wide range of user communities.
Small number of users with local needs.
Full infrastructure networks roaming over a broad area.
http://www.WirelessLAN.com
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Disadvantage of Wireless LAN
Cost
Wireless network cards cost 4 times more than wired network cards.
The access points are more expensive than hubs and wires.
Signal Bleed Over
Access points pick up the signals of adjacent access points or overpower their
signal.
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Disadvantage of Wireless LAN
Environmental Conditions
Susceptible to weather and solar activity.
Constrained by buildings, trees, terrain.
Less Capacity
Slower bandwidth.
Limit to how much data a carrier wave can transmit without lost packets impacting
performance.
http://www.Compaq.com
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Wireless LAN Applications
Medical Professionals
Education
Temporary Situations
Airlines
Security Staff
Emergency Centers
R t HUB B id & S it h
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Repeater, HUB, Bridge & Switch
REPEATER, HUB, BRIDGE ANDSWITCH
Repeater Hub Bridge & Switch
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Repeater
A repeater receives a signal, regenerates it, and passes
on.It can regenerate and retime network signals at the level to allow them to travel a longer distance on tmedia.
It operates at Physical Layer of OSI
The Four Repeater Rule for 10-Mbps Ethernet should
used as a standard when extending LAN segments.This rule states that no more than four repeaters can used between hosts on a LAN.
This rule is used to limit latency added to frame travel each repeater.
Repeater, Hub, Bridge & Switch
Repeater Hub Bridge & Switch
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HubHubs are used to connectmultiple nodes to a singlephysical device, whichconnects to the network.Hubs are actually multiportrepeaters.
Using a hub changes thenetwork topology from a linearbus, to a star.
With hubs, data arriving over
the cables to a hub port iselectrically repeated on all theother ports connected to thesame network segment, exceptfor the port on which the datawas sent.
Repeater, Hub, Bridge & Switch
Repeater Hub Bridge & Switch
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Bridge
Bridges are used to logically separatenetwork segments within the same
network.They operate at the OSI data link layer(Layer 2) and are independent of higher-layer protocols.
The function of the bridge is to makeintelligent decisions about whether ornot to pass signals on to the next
segment of a network.When a bridge receives a frame on the
network, the destination MAC address is
looked up in the bridge table to
determine whether to filter, flood, or
copy the frame onto another segment
Broadcast Packets are forwarded
Repeater, Hub, Bridge & Switch
Repeater Hub Bridge & Switch
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Switch
Switches are Multiport Bridges.
Switches provide a unique network segment onport, thereby separating collision domains.
Today, network designers are replacing hubs in wiring closets with switches to increase their neperformance and bandwidth while protecting existing wiring investments.
Like bridges, switches learn certain information the data packets that are received from vacomputers on the network.
Switches use this information to build forwarding to determine the destination of data being sent bcomputer to another computer on the network.
Repeater, Hub, Bridge & Switch
Repeater Hub Bridge & Switch
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Switches: Dedicated Access
Hosts have direct connection
to switchFull Duplex: No collisions
Switching: A-to-A and B-to-Bsimultaneously, no collisions
Switches can be cascaded toexpand the network
Repeater, Hub, Bridge & Switch
switch
A
AB
C
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Introduction to IEEE 802.11 Protocol
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Why Standard?
Multi Vender inter operability
Protects customer investment Economies of scale
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What is 802.11?
802.11 is an IEEE standard for MAC and Physical Layer for Wireless Loca
Area Network (WLAN).
IEEE 802 11 Wireless LAN Standa
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IEEE 802.11 Wireless LAN Standa
In response to lacking standards, IEEE developed the first internatio
recognized wireless LAN standard IEEE 802.11
IEEE published 802.11 in 1997, after seven years of work
Most prominent specification for WLANs
Scope of IEEE 802.11 is limited to Physical and Data Link Layers.
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802.11 Versions
802.11 - 1997
Maximum data rate: 2Mbps
2.4Ghz band
Indoor Range: 20 meters
Outdoor Range: 100 meters
Wide range of Physical layers
802.11a - 1999
Maximum data rate: 54Mbps
5.1 - 5.8Ghz band
Indoor range: 35 meters
Outdoor range: 120 meters
54 Mbps
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802.11 Versions
802.11b - 1999
Maximum data rate: 11Mbps
2.4Ghz band
Indoor Range: 38 meters
Outdoor Range: 140 meters
11 Mbps
802.11g - 2003
The current industry adopted specification
Maximum data rate: 54Mbps
2.4Ghz band (backwards compatible with 802.11b)
Indoor range: 38 meters
Outdoor range: 140 meters
54 Mbps
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What is WiFi?
A trademark of the Wi-Fi Alliance
Founded in 1999 as WECA (Wireless Ethernet Compatibility Alliance).
More than 300 companies
WiFi certification warrants interoperability between different wirelessdevices
Ensures correct implementation IEEE 802.11
Tests the wireless components to their own terms of reference
Physical Media Defined by Origin
http://upload.wikimedia.org/wikipedia/en/3/32/Wi-Fi_Logo.svg -
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Physical Media Defined by Origin802.11 Standard
Frequency-hopping spread spectrum
Operating in 2.4 GHz ISM band
Lower cost, power consumption
Most tolerant to signal interference
Direct-sequence spread spectrum
Operating in 2.4 GHz ISM band
Supports higher data rates
More range than FH or IR physical layers
Infrared
Lowest cost
Lowest range compared to spread spectrum
Doesnt penetrate walls, so no eavesdropping
Frequency Hopping Spread
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Frequency Hopping SpreadSpectrum
Signal is broadcast over seemingly random sof radio frequencies
Signal hops from frequency to frequency atfixed intervals
Receiver, hopping between frequencies insynchronization with transmitter, picks up
messageAdvantages
Efficient utilization of available bandwidth
Eavesdropper hear only unintelligible blips
Attempts to jam signal on one frequency succee
only at knocking out a few bits
Direct Sequence Spread Spectrum
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Direct Sequence Spread Spectrum
Each bit in original signal is represented by multiple bits in the transignal
Spreading code spreads signal across a wider frequency band DSSS is the only physical layer specified for the 802.11b specificatio
802.11a and 802.11b differ in use of chipping method
802.11a uses 11-bit barker chip
802.11b uses 8-bit complimentary code keying (CCK) algorithm
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Basic Service Set (BSS)
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Extended Service Set (ESS)
Portal
Distribution System
Authentication
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Authentication
Authentication
Prove identity to anotherstation.
Open system authentication
Shared key authentication
A sends
B responds with a text
A encrypt and send back
B decrypts and returns anauthenticationmanagement frame.
May authenticate anynumber of station.
Security Problem
A rogue AP SSID of ESS
Announce its presencewith beaconing
A active rogue reachhigher layer data if
unencrypted.
CSMA/CD vs. CSMA/CA
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CSMA/CD CSMA/Collision detection
For wire communication
No control BEFORE transmission Generates collisions
Collision Detection-How?
CSMA/CA CSMA/Collision Avoidance
For wireless communication
Collision avoidance BEFORE transmission Why avoidance on wireless?
Difference in energy/power for transmit & receive
Difficult to distinguish between incoming weak signanoise, and effects of own transmission
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Authentication Frame Sequence
Station APAuthentication Request 1
(authentication Type)
Authentication Response 1
Challenge Text
Authentication Request 2
Encrypted packet
Authentication Response 2
Pass/Fail
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RTS CTS Frame Sequence
Station AP
RTS
CTS
Data
ACK
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Comparison