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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 & the5) 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 TechnologiesWill Continue To Increase In DemandCalled "Wireless Ethernet" or "Bluetooth"

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BSS - Building Block Of Wireless LANsStationary Or Wireless WorkstationsPossible 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) - CalledAn Infrastructure Network

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5 Physical Layer Specifications

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IEEE 802.11

FHSS

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Signal Generation In A 2.4 GHz BandSender Sends On One Frequency Band For

Short Period Of TimeThen Hops To Another For That Same Period

Of TimeThen 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 - 2 802.11

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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 GHz79 Subbands of 1 MHzBuilt In Pseudo-Random Generator Selects

Hoppin SequenceFSK (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 EncodingFSK - 1

FSK – Frequency Shift Keying – Vary The Frequency

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IEEE 802.11

DSSS

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Signal Generation In A 2.4 GHz ISM BandEach 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 AtPhysicalLayer

802.11

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Digital-To-Analog EncodingPSK - 1

PSK – Phase Shift Keying – Vary The Phase

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IEEE 802.11a

OFDM

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Signal Generation In A 5 GHz ISM BandThe Difference Between FDM and OFDM

Is That OFDM Uses All Frequencies Within A Band Are Used Simultaneously By 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 MbpsThe QAM Data Rate Is 54 Mbps

OFDM - Orthogonal Frequency- Division Multiplexing - 2 802.11a

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Digital-To-Analog EncodingQAM

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Digital-To-Analog EncodingQAM

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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 DSSSDefines 4 Data Rates

1 or 2 Using PSK5.5 Using BPSK11 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

802.11bSignal Reflection

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CSMA/CD Flowcharts

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CSMA/CD Is An Acronym For

Carrier Sense MultipleAccess With Collision

Detection

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CSMA/CD ProcedureWired - Chapter 13 - 3 Problems

I. CD Implies Station Must Be Able To SendData & 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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AddressingMechanism

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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

ToDS

FromDS

Address1

Address2

Address3

Address4

0 0Destination

stationSourcestation

BSS ID N/A

0 1Destination

stationSending

APSourcestation

N/A

1 0Receiving

APSourcestation

Destinationstation

N/A

1 1Receiving

APSending

APDestination

stationSourcestation

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Addressing Mechanism 0 0 Frame Is Coming From A Station & Going To A Station

ToDS

FromDS

Address1

Address2

Address3

Address4

0 0 Destinationstation

Sourcestation

BSS ID N/A

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Addressing Mechanism 0 1 Frame Is Coming From An AP & Going To A Station

ToDS

FromDS

Address1

Address2

Address3

Address4

0 1 Destinationstation

SendingAP

Sourcestation

N/A

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Addressing Mechanism 1 0 Frame Is Coming From A Station & Going To An AP

ToDS

FromDS

Address1

Address2

Address3

Address4

1 0 ReceivingAP

Sourcestation

Destinationstation

N/A

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Addressing Mechanism 1 1 Frame Is Coming From An AP & Going To An AP

ToDS

FromDS

Address1

Address2

Address3

Address4

1 1 ReceivingAP

SendingAP

Destinationstation

Sourcestation

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BlueTooth802.15

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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 Transmitter 1 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 NetworksBy Andrew Tanenbaum

Textbook: Data Communications & NetworkingBy 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."