COS 125

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COS 125

• Day 3

2
Agenda

• Questions from last Class??
• Todays topics
• Connecting to the Internet
• Assignment 1 is due on Feb 5
• Quiz 1 on Feb 12
• Chap 1-26
• 20 M/C, 4 short essays, One extra credit Question
• 60 Min, open book, open notes

3
Connecting to the Internet

• Lots of ways to connect with more being invented
• General rule faster is better
• In order of speed
• Direct LAN connection
• Cable modem or DSL
• Telephone modem
• Newest way is wireless
• WiFi, Cellular WiMAX

4
Where do you get Internet Service

• ISPs
• St. John Valley Communications
• Pivot. net
• Earthlink
• Bluelight
• Online Service
• AOL
• MSN

5
How a modem works

• Modems allow digital signals to go over an analog
  circuit
• Analog Data
• Smooth changes among an infinite number of
  stateslike hands going around an analog clock
• Digital Data
• Few 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?

On/Off Switch
Number Of Fingers
Calendar
Clock
TV
Audio CD
7
Sending data with a modem
Modulated Analog Signal
Telephone
Binary Data
1010010101
PSTN
Modem
Computer
Amplitude (Loudness or Intensity) Modulation
1
0
1
1
1011 becomes loud-soft-loud-loud
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Getting Data with a modem
Modulated Analog Signal
Demodulated Binary Data
Telephone
1010010101
PSTN
Modem
Computer
Amplitude (Loudness or Intensity) Modulation
1
0
1
1
Loud-soft-loud-loud becomes 1011
9
Modems

• Two types
• Internal
• External
• Computers control modems using the Hayes Command
  Set
• In the early days of the Internet (early 1990s)
  users had to program modem using Hayes command to
  connect to an ISP

10
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
Need Modem at Each End Up to 33.6 kbps
Analog Modulated Signal
Binary Data
Modem
Telephone
33.6 kbps Modem
Server A
Telephone
Client A
PSTN
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Figure 7.2 Telephone Modem Communication
PSTN
Digital Access Line
Server B
56 kbps Modem
Telephone
Client B
For 56 kbps Download Speed Server 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
ISP
2. Optical Fiber to Neighborhood
4. Coaxial Cable to Premises
3. Neighborhood Splitter
1. Cable Television Head End
5. Cable Modem
Subscriber Premises
PC
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//etv.go.com/etvHome/about.shtml
• A special receiver formats digital signals and
  overlays that information on the TV image
• Digital 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 doesnt 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
Subscriber Premises
Telephone Company End Office Switch
Data WAN
1. Existing Single Pair of Voice-Grade UTP Wires
ADSL Modem
PC
DSLAM
Splitter
3.
PSTN
2.
Telephone
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ASDL with Splitter
1. Data 256 kbps to 1.5 Mbps
Subscriber Premises
Telephone Company End Office Switch
Data WAN
2. 64 kbps to 256 kbps
ADSL Modem
PC
DSLAM
Splitter
PSTN
Telephone
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ASDL with Splitter
Subscriber Premises
Telephone Company End Office Switch
Data WAN
ADSL Modem
PC
DSLAM
Splitter
PSTN
1. Ordinary Telephone Service
Telephone
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Old Online services

• Available prior to public internet service (ISPs
  1995)
• BBS (bulletin board service)
• AOL, Prodigy, CompuServe
• Some local BBSs
• 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

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WiFi

• 802.11 standards
• 802.11b
• 11Mbps _at_ 2.4 GHz
• 802.11a
• 54 Mbps _at_ 5 GHz
• 802.11g
• 54 Mbps _at_ 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
Access Point
Industry Standard Coffee Cup
Wireless Notebook NIC
Antenna (Fan)
To Ethernet Switch
PC Card Connector
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Typical 802.11 Wireless LAN Operation with Access
Points
CSMA/CAACK
Switch
UTP
Radio Link
Access Point A
Notebook
UTP
Handoff If mobile computer moves to
another access point, it switches service to that
access point
Access Point B
Client PC
Server
Large Wired LAN
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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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Satellite Internet
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Orbits
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GEO Satellite System
1. Geosynchronous Satellite
2. Point-to-Point Uplink
3. Broadcast Downlink
4. Footprint
5. Earth Station A
Earth Station B
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 Pages
• WAP
• Wireless access protocol
• WML
• 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 peripherals
• Personal Area Network
• Does not provide Internet Access
• Limited range

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Personal Area Networks (PANs)

• Connect Devices On or Near a Single Users Desk
• PC, Printer, PDA, Notebook Computer, Cellphone
• Connect Devices On or Near a Single Users Body
• Notebook Computer, Printer, PDA, Cellphone
• The Goal is Cable Elimination

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Personal Area Networks (PANs)

• There May be Multiple PANs in an Area
• May overlap
• Also called piconets

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802.11 versus Bluetooth LANs
802.11
Bluetooth
Focus
Large WLANs
Personal Area Network
Speed
11 Mbps to 54 Mbps In both directions
722 kbps with back channel of 56 kbps. May
increase.
Distance
100 meters for 802.11b (but shorter in reality)
10 meters (may increase)
Number of Devices
Only 10 piconets, each with 8 devices maximum
Limited in practice only by bandwidth and traffic
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802.11 versus Bluetooth LANs
802.11
Bluetooth
Scalability
Good through having multiple access points
Poor (but may get access points)
Cost
Probably higher
Probably Lower
Battery Drain
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
Notebook Master
File Synchronization
Client PC Slave
Printing
Printer Slave
Piconet 1
Cellphone
Telephone
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Figure 5.11 Bluetooth Operation
Notebook
Client PC
Printing
Printer Slave
Call Through Company Phone System
Cellphone Master
Telephone Slave
Piconet 2
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Figure 5.11 Bluetooth Operation
Notebook Master
File Synchronization
Client PC Slave
Printing
Printer Slave
Piconet 1
Call Through Company Phone System
Cellphone Master
Telephone Slave
Piconet 2
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Home Networks

• Many Homes have more than one computer or
  Internet Device
• Dont want to provide Internet to each device
  independently
• Connect all device to a network and provide
  Internet access to the Home networks
• Sometimes 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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Smart House

• If your home has a network then can get
• Internet enabled appliance
• Control systems that you can access from
  anywhere
• Security systems
• Places to check
• http//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?