Transcript COS 125 day 3 - Ecom and COS classes

COS 125
Day 3
Agenda
Questions from last Class??
 Today’s 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

Connecting to the Internet
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Lots of ways to connect with more being
invented
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General rule >>> faster is better
In order of speed
Telephone modem
 Cable modem or DSL
 Direct LAN connection
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Newest way is wireless
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WiFi, Cellular, WiMAX
Where do you get Internet Service

ISPs
St. John Valley Communications
 Pivot.net
 EarthLink
 Bluelight
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Online Service
AOL
 MSN
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How a modem works
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Modems allow digital signals to go over
an analog circuit
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Analog Data
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Smooth changes among an infinite number of
states—like 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
Sending data with a modem
Modulated Analog
Signal
Binary Data
Telephone
1010010101
PSTN
Modem
Computer
Amplitude (Loudness or Intensity) Modulation
1
0
1
1011 becomes loud-soft-loud-loud
1
Getting Data with a modem
Modulated Analog
Signal
Demodulated
Binary Data
Telephone
1010010101
PSTN
Modem
Computer
Amplitude (Loudness or Intensity) Modulation
1
0
1
Loud-soft-loud-loud becomes 1011
1
Modems

Two types
Internal
 External
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Computers control modems using the
Hayes Command Set
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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
Modem Speeds
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V.34
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Send and receive at up to 33.6 kbps
Fall back in speed if line conditions are not optimal
V.90
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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
Modem Speeds
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V.92
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Receive at up to 56 kbps
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Send at up to 33.6 kbps or higher if the line permits
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Other party must have a digital connection to the
PSTN
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Modem on hold: can receive an incoming call for a
short time without losing the connection

Cuts call setup time in half
Telephone Modem Communication
Need Modem at Each End Up to 33.6 kbps
Binary Data Analog Modulated
Signal
Client A
33.6 Telephone
kbps
Modem
Telephone
PSTN
Modem
Server A
Figure 7.2: Telephone Modem
Communication
PSTN
Digital Access Line
Client B
56 kbps
Modem
Telephone
Server
B
For 56 kbps Download Speed
Server Must Have a Digital Connection (ISDN PRI), Not a Modem
How Internet TV works

TV was the first “Information Super highway”
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The internet allows Interactive use

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Able to move of lot of info to the user
Problem was User could not interact with the info
Unidirectional
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
Cable Modem Services
ISP
2. Optical
Fiber to
Neighborhood
4. Coaxial
Cable to
Premises
3.
Neighborhood
Splitter
PC
5. Cable
Modem
Subscriber
Premises
6. Requires NIC or USB port
1. Cable
Television
Head End
MSN TV

Can watch TV and get on the Internet at the
same time
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Requires
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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
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
image

Digital information is interactive WWW
HTML
Digital Subscriber Lines

Uses existing Phone lines to get very high
speed Internet Access
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Up to 55 Mbps (1000 times faster than a V.90
modem)
Normal speeds for ADSL is 384 kbps down/ 96
kbps up
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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
ASDL with Splitter
Subscriber
Premises
Telephone Company
End Office Switch
Data
WAN
PC
ADSL
Modem
Splitter
2.
Telephone
1.
Existing
Single Pair of
Voice-Grade
UTP Wires
DSLAM
3.
PSTN
ASDL with Splitter
Subscriber
Premises
PC
ADSL
Modem
Splitter
1.
Data
256 kbps to
1.5 Mbps
Telephone Company
End Office Switch
Data
WAN
2.
64 kbps to
256 kbps
DSLAM
PSTN
Telephone
ASDL with Splitter
Subscriber
Premises
Telephone Company
End Office Switch
Data
WAN
PC
ADSL
Modem
DSLAM
Splitter
Telephone
1.
Ordinary Telephone
Service
PSTN
How DSL works

ADSL
UP < Down
 Uses POTS
 Distance effects
Bandwidth
 Phone service is
normal
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Old Online services
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Available prior to public internet service (ISPs
~ 1995)
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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

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Applications, pictures, music
Required subscription fees and phone access
Never really popular in rural areas
Modern Online Services
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Internet Plus
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Gives access to all (or most) of the Internet through
gateways
Several Propriety applications
Lost of data “firewalled” away from the Internet
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“Walled gardens”
Most common is AOL and MSN
Both use TCP/IP
Great for Internet Novices

Much greater control over Spam, viruses
How Wireless works
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All sorts of devices
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Laptops
PDA
Cell phones
Peripherals
Many types of wireless
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WiFi
Satellite
Bluetooth
Cellular
WiMAX
WiFi
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802.11 standards
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802.11b
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802.11a
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54 Mbps @ 5 GHz
802.11g
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11Mbps @ 2.4 GHz
54 Mbps @ 2.4 GHz
Devices must have a WiFi card and they
connect to Wireless Access Points (Hot spots)
WiFi
Typical 802.11 Wireless LAN
Operation with Access Points
Access Point
Industry
Standard
Coffee
Cup
Antenna
(Fan)
Wireless
Notebook
NIC
PC Card
Connector
To Ethernet
Switch
Typical 802.11 Wireless LAN
Operation with Access Points
CSMA/CA+ACK
Switch
UTP
Radio Link
Access
Point A
UTP
Access
Point B
Client PC
Server
Large Wired LAN
Notebook
Handoff
If mobile computer
moves to another
access point,
it switches service
to that access point
Wardriving
War Drive How To
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Equipment needed
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Car
Another person (prevents accidents!)
Laptop with wireless access
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Netstumbler software
GPS unit
Drive around till Netstumbler detects an access point
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Wireless antenna optional
Analyze access point
Record coordinates using GPS
Mark on Electronic Map
Chalk mark sidewalk
Why?
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Most access points are not secure (no WEP)
Allows free internet access
Hackers use as entry points to get to other more secure networks
Chalk Symbols
WiMAX
802.16 standard
 Uses cell towers
 Home or pc based

http://computer.howstuffworks.com/wimax1.htm
Satellite Internet
Orbits
GEO Satellite System
2. Point-to-Point
Uplink
1.
Geosynchronous
Satellite
3.
Broadcast
Downlink
5. Earth Station A
4.
Footprint
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
Wireless Internet Access for small
devices
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Cell phones and PDA do not have big
enough screens for full size Web Pages
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WAP
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WML
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Wireless access protocol
Wireless markup language
WAP gateways converts regular HTML
to WML and vice versa
WAP
BlueTooth
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Wireless networks for peripherals
Personal Area Network
 Does not provide Internet Access
 Limited range
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Personal Area Networks (PANs)
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Connect Devices On or Near a
Single User’s Desk
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Connect Devices On or Near a
Single User’s Body
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PC, Printer, PDA, Notebook
Computer, Cellphone
Notebook Computer, Printer,
PDA, Cellphone
The Goal is Cable Elimination
Personal Area Networks (PANs)
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There May be Multiple PANs in an Area
May overlap
 Also called piconets

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)
Number
of Devices
Limited in practice only
by bandwidth and traffic
10 meters
(may increase)
Only 10 piconets,
each with
8 devices maximum
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
Figure 5.11: Bluetooth
Operation
Notebook
Master
Printing
File Synchronization
Printer Slave
Piconet 1
Cellphone
Telephone
Client PC
Slave
Figure 5.11: Bluetooth
Operation
Notebook
Client PC
Printing
Printer Slave
Call Through Company
Phone System
Cellphone
Master
Piconet 2
Telephone Slave
Figure 5.11: Bluetooth
Operation
Notebook
Master
Printing
Piconet 1
File Synchronization
Printer Slave
Call Through Company
Phone System
Cellphone
Master
Piconet 2
Telephone Slave
Client PC
Slave
Home Networks

Many Homes have more than one
computer or Internet Device
Don’t want to provide Internet to each
device independently
 Connect all device to a network and provide
Internet access to the Home networks

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Sometimes called SOHO networks
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SOHO >> small office/home office
Needed to build home Networks
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Internet Access
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Broadband DSL or Cable modem
A way to connect all devices
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Wired with Ethernet
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Wireless (WiFi)
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Easier & Cheaper
A network Address Scheme
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Most broadband device provide DHCP
Use Microsoft Internet Connection Sharing
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Hub or Switch
Expensive
ME, XP, Windows NT
Firewall

Keep hackers out
WiFi Home network
Wireless Media
Get rid of wiring
 PPP or Multi
 http://www.dlink.com
/products/?pid=318
 Wireless Speakers

Smart House

If your home has a network then can get
Internet enabled appliance
 Control systems that you can access from
anywhere
 Security systems
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Places to check
http://www.smarthomeusa.com/
 http://www.smarthome.com/index.html

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?
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