![Page 1: Data Communication & Networking CSCI 3342carme.cs.trinity.edu/thicks/3342/Lectures/DCN-15-16-WirelessLANs-Slides.pdf · 802.11g's big advantages over 802.11b - it handles the inevitable](https://reader033.vdocuments.us/reader033/viewer/2022042006/5e7029c5b168d6338c6dcc1d/html5/thumbnails/1.jpg)
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Dr. Thomas HicksComputer Science Department
Trinity University 1
Data Communication
& Networking CSCI 3342
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IEEE
802.11
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A _?_ is a networking device that forwards
data packets between computer
networks.
Router
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A _?_ performs the "traffic directing" functions on the
Internet.
Router
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A _?_ can manage the DHCP for a
wireless network.
Router
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The Wi-Fi Signal Range depends on :
1) Frequency Band,
2) Radio Power Output,
3) Antenna Gain,
4) Antenna Type & the
5) Modulation Technique
Line-of-Sight is the Thumbnail Guide but Reflection and Refraction can have a significant impact.
WiFi – Line Of Sight
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Router
A Router is a networking device that forwards data packets between computer networks.
Routers perform the "traffic directing" functions on the Internet.
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Access Point
A Wireless Access Point (AP) is a device that allows wireless devices to connect to a wired network using Wi-Fi, or related standards.
The AP usually connects to a router as a standalone device, but it can also be an Integral Component of the Router Itself."
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802.11b or 802.11g Range
An Access Point, using a stock antenna can have a range of 100 m/330 ft.
The Same AP Radio with - using an external semi Parabolic Antenna - could have a range over 20 miles.
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Overview - Wireless LANs
One Of Fastest Growing Technologies
Will Continue To Increase In Demand
Called "Wireless Ethernet" or "Bluetooth"
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BSS - Building Block Of Wireless LANsStationary Or Wireless Workstations
Possible Central Base Called An Access Point
Without An Access Point - Can't Send Data To Other BSS's - No Internet - Can Connect To Each Other
Basic Service Set (BSS)
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ESS - Two Or More BSS's With AP's
BSS's Are Connected Through A Distribution Center [Lot Less Traffic Than Uplinking Them!]
Can Be Mobile And/Or Hard Wired!
Extended Service Set (ESS) - Called
An Infrastructure Network
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5 Physical Layer Specifications
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IEEE
802.11FHSS
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Signal Generation In A 2.4 GHz Band
Sender Sends On One Frequency Band For Short Period Of Time
Then Hops To Another For That Same Period Of Time
Then To Another. Etc.
After N [N=5 in Example] Hops, Repeats The Sequence.
FHSS - Frequency-Hopping Spread
Spectrum - 1
Physical Layer - Why Do?
802.11
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Spreading The Signal Makes It More Difficult For Unauthorized People To Make Sense Of The Data
The Sender & Receiver Negotiate The Order In Which The Bands Are Used Making It More Difficult To Intercept
Dwell Time - The Amount Of Time Spent In Each Frequency - 400 ms or more
FHSS - Frequency-Hopping Spread
Spectrum - 2802.11
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FHHS Uses a 2.4 GHz ISM Band
ISM - Industrial, Scientific, & Medical
In North America
FHHS Is 2.4 GHz - 2.48 GHz
79 Subbands of 1 MHz
Built In Pseudo-Random Generator Selects Hoppin Sequence
FSK (1-2 bit) Allow Data Rate of 1 or 2 Mbps
FHSS - Frequency-Hopping Spread
Spectrum - 3 802.11
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Digital-To-Analog Encoding
FSK - 1
FSK – Frequency Shift Keying – Vary The Frequency
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IEEE
802.11DSSS
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Signal Generation In A 2.4 GHz ISM Band
Each Bit Sent By Sender Is Replaced By A Sequence Of Bits Called A Chip Code.
To Avoid Buffering, The Time To Send One Chip Code Must Be The Same As The Time To Send One Bit.
Thus The Chip Code Data Rate Must Be N Times The Normal Bit Stream Rate.
Uses PSK - 1 or 2 Mbps
DSSS - Direct Sequence Spread
Spectrum - 1
Implemented At
Physical
Layer
802.11
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Digital-To-Analog Encoding
PSK - 1
PSK – Phase Shift Keying – Vary The Phase
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IEEE
802.11aOFDM
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Signal Generation In A 5 GHz ISM Band
The Difference Between FDM and OFDM Is That OFDM Uses All Frequencies Within A Band Are Used SimultaneouslyBy One Sender.
Senders Contend At Data Link Layer
52 Subbands - 4 Used For Control -Sends 48 bits At A Time
OFDM - Orthogonal Frequency-
Division Multiplexing - 1 802.11a
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52 Subbands - 4 Used For Control -Sends 48 bits At A Time
The Subbands Reduce Interference -Randomly Mixing The Subbands Increases Security
The PSK Data Rate Is 18 Mbps
The QAM Data Rate Is 54 Mbps
OFDM - Orthogonal Frequency-
Division Multiplexing - 2 802.11a
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Digital-To-Analog Encoding
QAM
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Digital-To-Analog Encoding
QAM
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IEEE
802.11bHR-DSSS
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Similar To DSSS Except Encoding Method
Uses Complementary Code Keying Encoding
802.11bHR-DSSS - High-Rate Direct Sequence
Spread Spectrum - 1
Each Bit Sent By Sender Is Replaced By A Sequence Of Bits Called A Chip Code.
To Avoid Buffering, The Time To Send One Chip Code Must Be The Same As The Time To Send One Bit.
Thus The Chip Code Data Rate Must Be N Times The Normal Bit Stream Rate.
Signal Generation In A 2.4 GHz ISM Band
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HR-DSSS - High-Rate Direct Sequence
Spread Spectrum - 2
Backward Compatible With DSSS
Defines 4 Data Rates
1 or 2 Using PSK
5.5 Using BPSK
11 Mbps Using QPSK
Uses Complementary Code Keying Encoding
802.11b
http://www.eetkorea.com/ARTICLES/2001MAY/2001MAY25_NTEK_DSP_AN.PDF
802.11b's 11 Mbps raw throughput
generally translated to 4 to 6 Mbps
at best [ Adam Engst and Glenn
Fleishman]
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How Many Of You Have A Wireless Device Using
802.11b?
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IEEE
802.11g
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802.11g - 1
Similar To 802.11b Except It Uses An Even More Complex Encoding Method That Encodes Bits On Radio Waves. [Somewhat Similar To How DSL Encodes To Copper]
Data Rate Is 54 Mbps
802.11g is attractive because it includes full backwards compatibility with 802.11b
802.11g also has several intermediate steps for speed, so you don't just drop from 54 Mbps all the way down to 11 Mbps
802.11g
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"As is the case with most theoretical network throughputs, the net throughput of real data--the actual contents of files or transactions--provides somewhere between 20 and 30 Mbps" [ Adam Engst and Glenn Fleishman]
http://www.oreillynet.com/pub/a/wireless/2003/01/23/80211g.html
802.11g's big advantages over 802.11b - it handles the inevitable signal reflection better. Radio signals bounce off different things--floors, metal, even the air around you--at different angles and speeds. A receiver must reconcile all the different reflections of the same signal that arrive at slightly different times into a single set of data. [ Adam Engst and Glenn Fleishman]
802.11g802.11g - 2
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http://www.wikipedia.org/wiki/IEEE_802.11#802.11g
Wi-Fi Ratifies 802.11g Late Summer of 2003
802.11g802.11g - 3
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http://www.oreillynet.com/pub/a/wireless/2003/08/08/wireless_throughput.html
802.11g - 4 Intermediate Speeds
http://www.iapplianceweb.com/story/OEG20020402S0034
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Tell Me About The
Intermediate Speeds Of 802.11g?
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802.11g Handles _____ Better Than 802.11b
Signal Reflection
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CSMA/CD
Flowcharts
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CSMA/CD Is An Acronym For
Carrier Sense Multiple
Access With Collision
Detection
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CSMA/CD ProcedureWired - Chapter 13 - 3 Problems
I. CD Implies Station Must Be Able To Send
Data & Receive Collisions At Same Time
Would Require More Cost & Bandwidth!
II. Stations A & B Communicate With Each
C, But Can't Reach Each Other Because Of
Terrain. Collision Shall Occur Near C - No
Voltage On Wire!
III. Signal Fades Because It Will Not
Carry From Station A To B.
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CSMA/CD ProcedureWireless - Chapter 15
I. Sense The Medium By Checking Energy At
Frequency Until Clear
II. Once Idle - Waits DIFFS [Distributed Interframe
Space] - Sends Request To Send
III. After Receiving RTS & Waiting A SIFS [Short
Interframe Space] The Destination Sends A Clear To
Send
IV. Sending & Receiving Occur!
NAV?
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Figure 15.8 CSMA/CA and NAV
NAV - Network Allocation Vector - Is The Key
Feature Of Wireless Collision Avoidance.
The RTS (Request To Send) Includes A Timer That Shows
How Much Time Will Be Required To Complete The
Transmission.
Two Frames May Collide - Assumed If Not CTS Received.
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WirelessFrames
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Frame Format
Control Frames
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Addressing
Mechanism
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Addressing Mechanism
Addressing Mechanism Is Complex & Complicated Because There May Be Intermediate Stations (AP's)
4 Cases [Defined By The Values Of Two Flags - From DS To DS
802.11g
To
DS
From
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0 0Destination
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stationBSS ID N/A
0 1Destination
station
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stationN/A
1 0Receiving
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stationN/A
1 1Receiving
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Sending
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Addressing Mechanism 0 0
Frame Is Coming From A Station & Going To A Station
To
DS
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Address
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0 0 Destination
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Addressing Mechanism 0 1
Frame Is Coming From An AP & Going To A Station
To
DS
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1
Address
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Address
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0 1 Destination
station
Sending
AP
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station
N/A
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Addressing Mechanism 1 0
Frame Is Coming From A Station & Going To An AP
To
DS
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Address
1
Address
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Address
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1 0 Receiving
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Addressing Mechanism 1 1
Frame Is Coming From An AP & Going To An AP
To
DS
From
DS
Address
1
Address
2
Address
3
Address
4
1 1 Receiving
AP
Sending
AP
Destination
station
Source
station
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Blue
Tooth802.15
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Blue Tooth - 1
Blue Tooth Is A Wireless LAN Technology Designed To Connect Devices Of Different Functions
Telephones
Notebooks
Computers
PDA's
Other Devices That We Haven't Thought Of Yet!
Ad Hoc Network - Network Is Formed Spontaneously
Devices Called Gadgets
Device Has Short Range Radio Transmitter1 Mbps In A 2.4 GHz Band - 802.11b Can Interfere!
May or May Not Have Internet Access!
802.15
Printers
Coffee Makers
Security Systems
Cameras
Wireless Mouse
Wireless Keyboard
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Blue Tooth - 2
Blue Tooth Was Developed By Ericksson -Named After Harold Blattand - King of Denmark Who United Norway & Denmark - Blattand Translates Into "Blue Tooth" In English.
Personal Area Network (PAN)
Blue Tooth Defines Two Types Of Networks
Piconet [Small Net] - Size Of A Room Or Hall
A ScatterNet - Two Or More Piconets
802.15802.15
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Up To 8 Active Stations In Piconet
One Station Is The Master
There Can Be 7 Active Slaves & Up To 8 Parked Slaves - Synchronized With Master, But Can Not Take Part In Communication Until Removed FromParked State => Becomes Active Station
802.15Blue Tooth - 3
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802.15Blue Tooth - 4
A Slave In One Piconet Can Be A Master In Another Piconet!
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Blue Tooth Layers
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Data Communications & Networking
CSCI 3342
Dr. Thomas E. HicksComputer Science Department
Trinity University
Textbook: Computer Networks
By Andrew Tanenbaum
Textbook: Data Communications & Networking
By Behrouz Forouzan
Special Thanks To WCB/McGraw-Hill For Providing Graphics For
Many Text Book Figures For Use In This Presentation.
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Library Complaint
Judi stormed up to the front desk of the library and said, "I have a complaint!"
"Yes, ma'am?"
"I borrowed a book last week and it was horrible!"
"What was wrong with it?"
"It had way too many characters and there was no plot whatsoever!"
The librarian nodded and said, "Ah. So you must be the person who took our phone book."
Bottle Trouble
A woman was trying hard to get the catsup to come out of the jar. During her struggle the phone rang so she asked her four-year old daughter to answer the phone.
"It's the minister, Mommy," the child said to her mother.
Then she added, "Mommy can't come to the phone to talk to you right now. She's hitting the bottle."