COS 125
description
Transcript of COS 125
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COS 125
Day 3
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Agenda
Questions from last Class??Today’s topics
Connecting to the InternetAssignment #1 is due on Feb 5Quiz #1 on Feb 12
Chap 1-2620 M/C, 4 short essays, One extra credit
Question60 Min, open book, open notes
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Connecting to the Internet
Lots of ways to connect with more being inventedGeneral rule >>> faster is better
In order of speedTelephone modemCable modem or DSLDirect LAN connection
Newest way is wirelessWiFi, Cellular, WiMAX
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Where do you get Internet Service
ISPsSt. John Valley CommunicationsPivot.net EarthLinkBluelight
Online ServiceAOLMSN
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How a modem works
Modems allow digital signals to go over an analog circuitAnalog Data
Smooth changes among an infinite number of states—like hands going around an analog clock
Digital DataFew states In a digital clock, each position can be in one of
ten states (the digits 0 through 9)
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Quiz
Which is Analog? Which is Digital?
Calendar Clock
NumberOf
Fingers
Audio CD
On/OffSwitch
TV
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Sending data with a modem
Computer
Modem
Telephone
PSTN
Modulated AnalogSignal
1 0 1 1
Amplitude (Loudness or Intensity) Modulation
1010010101
Binary Data
1011 becomes loud-soft-loud-loud
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Getting Data with a modem
Computer
Modem
Telephone
PSTN
Modulated AnalogSignal
1 0 1 1
Amplitude (Loudness or Intensity) Modulation
1010010101
DemodulatedBinary Data
Loud-soft-loud-loud becomes 1011
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Modems
Two types Internal External
Computers control modems using the Hayes Command Set In the early days of the Internet (early
1990’s) users had to program the modems using Hayes command set to connect to an ISP
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Modem Speeds
V.34 Send and receive at up to 33.6 kbps Fall back in speed if line conditions are not optimal
V.90 Receive at up to 56 kbps Send at up to 33.6 kbps Asymmetric speed is good for WWW service. Other party must have a digital connection to the
PSTN
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Modem Speeds
V.92
Receive at up to 56 kbps
Send at up to 33.6 kbps or higher if the line permits
Other party must have a digital connection to the PSTN
Modem on hold: can receive an incoming call for a short time without losing the connection
Cuts call setup time in half
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Telephone Modem Communication
PSTNClient A
Server A Telephone
Telephone33.6kbps
Modem
Binary Data Analog ModulatedSignal
Modem
Need Modem at Each End Up to 33.6 kbps
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Figure 7.2: Telephone Modem Communication
PSTN
Client B
ServerBTelephone
Digital Access Line
56 kbpsModem
For 56 kbps Download SpeedServer Must Have a Digital Connection (ISDN PRI), Not a Modem
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How Internet TV works
TV was the first “Information Super highway” Able to move of lot of info to the user Problem was User could not interact with the info Unidirectional
The internet allows Interactive use Greater bandwidth means TV like performance
http://wwitv.com/ Existing TV cable system also can bring you High
Speed Internet service TV and Internet are combined in some services like
MSN TV MSN bought out Web TV
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Cable Modem Services
PCSubscriberPremises
5. CableModem
4. CoaxialCable toPremises
2. OpticalFiber to
Neighborhood
3.Neighborhood
Splitter
ISP
1. CableTelevisionHead End
6. Requires NIC or USB port
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MSN TV
Can watch TV and get on the Internet at the same time Requires
MSN TV receiver (keyboard & mouse) Phone access TV
Receiver acts like a PC and TV receiver all at once
Uses a proprietary web browser and lots of proxy web servers
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Internet Enhanced TV
TV networks send both TV signal and digital information to your homes http://en.wikipedia.org/wiki/Interactive_television
A special receiver formats digital signals and overlays that information on the TV imageDigital information is interactive WWW
HTML
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Digital Subscriber Lines
Uses existing Phone lines to get very high speed Internet Access Up to 55 Mbps (1000 times faster than a V.90
modem) Normal speeds for ADSL is 384 kbps down/ 96
kbps up Pivot.net 768 kbps down/128 kbps up
On 24/7 and doesn’t interfere with regular phone usage
The faster the DSL speed the closer you must be to the phone company
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ASDL with Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
SubscriberPremises
Telephone CompanyEnd Office Switch
1.Existing
Single Pair ofVoice-GradeUTP Wires
PC
2. 3.
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ASDL with Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
SubscriberPremises
Telephone CompanyEnd Office Switch
PC
1.Data
256 kbps to1.5 Mbps
2.64 kbps to256 kbps
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ASDL with Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
SubscriberPremises
Telephone CompanyEnd Office Switch
PC
1.Ordinary Telephone
Service
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How DSL works
ADSLUP < DownUses POTSDistance effects
Bandwidth Phone service is
normal
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Old Online services
Available prior to public internet service (ISPs ~ 1995) BBS (bulletin board service) AOL, Prodigy, CompuServe Some local BBS’s Gave you email & chat only with other users of the
same online service Allowed file transfers up and down
Applications, pictures, music Required subscription fees and phone access Never really popular in rural areas
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Modern Online Services
Internet Plus Gives access to all (or most) of the Internet through
gateways Several Propriety applications Lost of data “firewalled” away from the Internet
“Walled gardens”
Most common is AOL and MSN Both use TCP/IP Great for Internet Novices
Much greater control over Spam, viruses
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How Wireless works
All sorts of devices Laptops PDA Cell phones Peripherals
Many types of wireless WiFi Satellite Bluetooth Cellular WiMAX
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WiFi
802.11 standards 802.11b
11Mbps @ 2.4 GHz
802.11a 54 Mbps @ 5 GHz
802.11g 54 Mbps @ 2.4 GHz
Devices must have a WiFi card and they connect to Wireless Access Points (Hot spots)
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WiFi
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Typical 802.11 Wireless LAN Operation with Access Points
WirelessNotebook
NIC
Access Point
IndustryStandard
CoffeeCup
To EthernetSwitch
Antenna(Fan) PC Card
Connector
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Typical 802.11 Wireless LAN Operation with Access Points
Switch
Client PCServer
Large Wired LAN
AccessPoint A
AccessPoint B
UTP Radio Link
HandoffIf mobile computermoves to another
access point,it switches serviceto that access point
Notebook
CSMA/CA+ACK
UTP
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Wardriving
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War Drive How To
Equipment needed Car Another person (prevents accidents!) Laptop with wireless access
Wireless antenna optional Netstumbler software GPS unit
Drive around till Netstumbler detects an access point Analyze access point Record coordinates using GPS Mark on Electronic Map Chalk mark sidewalk
Why? Most access points are not secure (no WEP) Allows free internet access Hackers use as entry points to get to other more secure networks
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Chalk Symbols
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WiMAX
802.16 standardUses cell towersHome or pc based
http://computer.howstuffworks.com/wimax1.htm
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Satellite Internet
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Orbits
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GEO Satellite System
2. Point-to-PointUplink
3.BroadcastDownlink
4.Footprint5. Earth Station A Earth Station B
1.Geosynchronous
Satellite
Satellite appears stationary in sky (35,785 km or 22,236 mi)Far, so earth station needs dish antenna
At speed of light takes 250 ms to travel distance
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Wireless Internet Access for small devices
Cell phones and PDA do not have big enough screens for full size Web PagesWAP
Wireless access protocolWML
Wireless markup language
WAP gateways converts regular HTML to WML and vice versa
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WAP
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BlueTooth
Wireless networks for peripheralsPersonal Area NetworkDoes not provide Internet AccessLimited range
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Personal Area Networks (PANs)
Connect Devices On or Near a Single User’s DeskPC, Printer, PDA, Notebook
Computer, CellphoneConnect Devices On or Near a
Single User’s BodyNotebook Computer, Printer,
PDA, CellphoneThe Goal is Cable Elimination
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Personal Area Networks (PANs)
There May be Multiple PANs in an AreaMay overlapAlso called piconets
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802.11 versus Bluetooth LANs
Focus
Speed
802.11 Bluetooth
Large WLANs Personal Area Network
11 Mbps to 54 MbpsIn both directions
722 kbps with backchannel of 56 kbps.
May increase.
Distance100 meters for 802.11b(but shorter in reality)
Numberof Devices
Limited in practice onlyby bandwidth and traffic
Only 10 piconets,each with
8 devices maximum
10 meters(may increase)
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802.11 versus Bluetooth LANs
Scalability
Cost
Battery Drain
802.11 Bluetooth
Good through havingmultiple access points
Poor(but may get
access points)
Probably higher Probably Lower
Higher Lower
Discovery No Yes
Discovery allows devices to figure out how to work together automatically
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Figure 5.11: Bluetooth Operation
File Synchronization
Client PCSlave
NotebookMaster
Printer SlavePrinting
Cellphone
Telephone
Piconet 1
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Figure 5.11: Bluetooth Operation
Client PC
Notebook
Printer SlavePrinting
Call Through CompanyPhone System
CellphoneMaster
Telephone Slave
Piconet 2
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Figure 5.11: Bluetooth Operation
File Synchronization
Client PCSlave
NotebookMaster
Printer SlavePrinting
Call Through CompanyPhone System
CellphoneMaster
Telephone Slave
Piconet 1
Piconet 2
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Home Networks
Many Homes have more than one computer or Internet DeviceDon’t want to provide Internet to each
device independentlyConnect all device to a network and provide
Internet access to the Home networksSometimes called SOHO networks
SOHO >> small office/home office
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Needed to build home Networks
Internet Access Broadband DSL or Cable modem
A way to connect all devices Wired with Ethernet
Hub or Switch Expensive
Wireless (WiFi) Easier & Cheaper
A network Address Scheme Most broadband device provide DHCP Use Microsoft Internet Connection Sharing
ME, XP, Windows NT Firewall
Keep hackers out
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WiFi Home network
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Wireless Media
Get rid of wiring PPP or Multihttp://
www.dlink.com/products/?pid=318
Wireless Speakers
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Smart House
If your home has a network then can get Internet enabled applianceControl systems that you can access from
anywhereSecurity systems
Places to checkhttp://www.smarthomeusa.com/http://www.smarthome.com/index.html
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For next class
Read through chapter 26 (page 187) Extra Credit Question on Next exam
How many Hackers have been arrested in Maine?
Can you name any successful prosecutions of Hackers in the state of Maine?
What is the problem in catching and prosecuting Hackers in Maine?