Transcript Networks

311: Management Information
Systems
Chapter 4: Telecommunications
And Networks
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Telecommunication Systems
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Network
• A Network is an Any-to-Any Communication
System
– Can connect any station to any other
• Each Station has a Unique Network Address
– To connect, only need to know the receiver’s address
– Like telephone number
GHI
DEF
ABC
MNO
“Connect to GHI”
JKL
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Transmission Media
• Twisted-Pair Wire
– Telephone wire, Cat 5
• Coaxial Cable
– Cable TV cable
• Fiber-Optic Cable
– 20 x price of twisted pair, 1000 x
capacity
• Microwave Signals
– ’No, you don’t get toasted!’
– Satellites, line-of-sight
• Infrared and Radio Signals
– Wireless, short distance
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Media Types
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Data Processing Strategies
• Centralized Processing
– all processing occurs in a single location or
facility
• Decentralized Processing
– processing devices are placed at various
remote locations
• Distributed Processing
– computers are placed at remote locations and
connected via telecommunication devices
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Terminal-to-Host Connection
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File Server Connection
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Client/Server Connection
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Client/Server Processing
• Cooperation Through Message Exchange
– Client program sends Request message, such as
a database retrieval request
– Server program sends a Response message to
deliver the requested information or an
explanation for failure
Server
Program
Client Program
Request
Response
Client Machine
Server
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Networks
• Local Area Network (LAN)
– Connect computers in a single building or campus
– Distances typically less than 1,000 meters
• Wide Area Networks (WAN)
– Connects computers across long distances
– Typically several hundred kilometers
– Example: Internet
• Metropolitan Area Networks (MAN)
– Connects computers in the same city
Not in Book
– Up to 100 kilometers (often much less)
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Network Types
• Ethernet
– Very popular, Cheap 10/100/1000 Mbps
– Usually short distances
• Asynchronous Transfer Mode (ATM)
– Good for multimedia. Used for Internet access.
– Up to 622 Mbps over long distances
• Bluetooth
– For connecting devices (printer, mouse etc) to PC.
Short range, piconet, Max 1 Mbps
• More wireless on next slide...
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Wireless alphabet soup
Spec
802.11b
(WiFi)
802.11a
(WiFi-5)
802.11g
Range
75 m
Speed
11 Mbps
Frequency
2.4 GHz
Risks interference w/ cordless phones
30 m
54 Mbps
5 GHz
Less interference
75 m
54 Mbps
2.4 GHz
Backwards compatible w/802.11b
• 802.11i – security standard
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The Internet
Traffic travels across
routers between LANs
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Technological Underpinnings
• Internet Management
– No owner! Managed by negotiation and non-binding contracts.
May not continue to work.
– Internet Engineering Task Force (www.ietf.org) decides on
technical standards
– World Wide Web Consortium (www.w3c.org) sets HTML and
HTTP standards
• Backbone network (gigabit connection)
– http://www.caida.org/tools/visualization/mapnet/Backbones/
• Network Addressing
– IP numbers: e.g. 140.252.13.33 (32 bits = 4 billion addresses)
– The internet is running out of addresses!
– Long-term solution: IP v6 (128 bits = 3.4 * 1038 addresses)
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More Technology…
• Domain Names
– Text version of IP address (translated by DNS)
– Country domains (.dk, .uk, .de, .us) and generic
domains (.com, .net, .org). USA also has .mil, .gov,
and .edu.
– NEW: .aero, .biz, .coop, .info,
.museum, .pro, .name
– Managed by ICANN (www.icann.org)
• Network Access
– No-one controls access!
– Most people connect through an ISP
• AOL and MSN largest ISPs (even though they are Online
Services (OLSs)
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Internet Protocols
• Internet Protocol (IP): standard that enables
traffic to be routed from one network to another
as needed
• Transport Control Protocol (TCP): rules that
computers on a network use to establish and
break connections
• Uniform Resource Locater (URL): an assigned
address on the Internet for each computer
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Internet Communication
• E-mail (first time in 1971!) • Streaming
– One of the most popular
activities on the Internet!
– Becoming official business
communication mode
– ListServ
(http://www.lsoft.com/lists/listref.html)
• Newsgroups (Usenet)
– Go to
http://www.google.com/grp
hp?hl=en
– Being outpaced by webbased fora
– Internet Radio, Internet TV
• Real-Time Streaming
•
•
•
•
•
– Videoconferencing
Chatting/IM
Online collaboration
Internet Telephony (VoIP)
Web log (blog)
Rich Site Summary (RSS)
– a.k.a. RDF Site Summary
• Telnet
• FTP
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World Wide Web (www)
• Hyper Text Transfer Protocol (HTTP)
• Hyper Text Markup Language (HTML)
– And derivatives/alternatives
Developed
in 1989
• SGML, DHTML, XML
• URL
• Browser
• Search engines
http://www.uwosh.edu
– Google most popular
– Categories: Web crawlers (e.g. Google), categorized (e.g.
Yahoo), Meta-search (search many engines)
– Info on search engines: www.searchenginewatch.com
• Review Question: What’s the difference between the
Internet and the Web?
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Types of Internet sites
• Portals
– A unified access site for many different
sites (e.g. Excite, Yahoo, ...)
– Can be topical (webMD), geographical
(www.denmark.dk)
•
•
•
•
•
E-commerce
Government
Special Interest Groups
Informational
...
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Internet Worldwide Trends
• Rapid worldwide growth continues
• Main use in
– North America, Europe, Australia
• Some use in
– Asia, Middle East, Eastern Europe, South America
• Virtually no use
– Africa (90% in South Africa)
• 80% of all international connections from Asia,
Africa, S. America go directly to a US city
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Worldwide Trends
• Online Population in million vs. World
Population
– Online: Jan. 2000 and Feb. 2002, Offline: Mid2000
Total Pop Online, 01-00 Online 02-02 Percent, 00 Percent, 02
Asia/Pacific
3444
40
157.49
1.2%
4.6%
South America
520
8
25.33
1.5%
4.9%
Europe
723
70
171.35
9.7%
23.7%
Middle East
170
1.9
4.65
1.1%
2.7%
Africa
805
2.1
4.15
0.3%
0.5%
Canada & USA
307
120
181.23
39.1%
59.0%
World Total
6080
242
544.2
4.0%
9.0%
Growth
293.7%
216.6%
144.8%
144.7%
97.6%
51.0%
124.9%
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Intranets and Extranets
• Intranet
– An internal corporate network built
using Internet and World Wide Web
standards and products; used by the
employees of the organization to
access corporate information.
• Accessed by on-site
employees
• Passwords needed
• Most company info
can be put on
intranet
• Extranet
– A network that links selected
resources of the intranet of a
company with its customers,
suppliers, or other business partners;
based on Web technologies.
• Accessed by off-site
employees and
business partners
• Passwords needed
• Example: Online
banking, TitanWeb
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Intranet and Extranet
• Both use internet
standards
– Web pages, HTTPprotocol
Extranet
• Intranet
– Within a company
• Extranet
– Outside access to a
company’s intranet or
specific web pages
– Security: Virtual Private
Networks (VPN)
Firewall
Intranet
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Electronic Data Interchange (EDI)
• A system to electronically transfer
business documents
– Orders, bills, confirmations etc
– ’Structured e-mail messages’
• Agreements/partnerships are set up in
advance
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Issues in EDI
• Data Standards
– ANSI X.12: Used in the US
– EDIFACT: Defined by UN. Used in much of the rest
of the world
– XML/EDI may help in the future
• http://www.geocities.com/WallStreet/Floor/5815/
– Companies must use the same standard to
communicate
– Standards can be tailored to fit industries or
individual businesses
• Mostly for large companies
– May force smaller business partners to use EDI
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Issues in EDI
• Two Network Standards
• Value Added Network (VAN)
– Pro: High security, high capacity
– Con: Price, incompatible hardware, only
large companies
• Internet
– Pro: Cheap, ubiqutous, easy to use
– Con: Security, capacity
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Virtual Private Network
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Ensuring Security of Information
and Access
• Firewalls
• Security Management
– Organizational procedures
• Encryption and digital signatures
• Secure Protocols
– E.g. HTTPS
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Encryption
Encryption: a process of
making messages
indecipherable except by
those who have an
authorized decryption key
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Single-key encryption
• The sender of the electronic message (or payment)
encrypts the information with a key
• The receiver uses an identical key to decrypt the
information to a readable form
• The same code has to be in the possession of both the
sender and the receiver
• Problems: if a key is transmitted or intercepted illegally,
it could be used to read all encrypted messages
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Public/private key encryption
• Two different keys - public key and private key
• Several authorized people may know the public key, but
only its owner knows the private key
• Every person has one private key and one public key
• Encryption and decryption can be done with either key
• If encryption is done with the public key, the decryption
can be done only with the private key and vice versa
• Problem: Slower than single-key encryption
• Try it out: go to
http://www.pgp.com/products/freeware.html
– Freeware version: No commercial use!
– 8.6 MB download
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Public/Private Key Encryption
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Coming Up
• Thursday
– Lab 4 due
• Tuesday
– Lecture on Chapter 5
– Note: GUI has been moved
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