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Networks, Internet & WWW
 Reading Materials:
 Ch 7 of [SG3]
 Additional Notes: (from web-site)
Spring 2012
 Contents:
 Motivation for Networks Networks not
covered in
 Types of Networks and Their Structure
Final Exams
 Communication Protocols – routing info
 Network Services / Applications
 Internet and WWW
Hon Wai Leong, NUS
(UIT2201, Networks) Page 1
Copyright © 2007 by Leong Hon Wai
Networks, Internet, WWW
 Context so far…
 Use algorithm to solve problem
 Database used to organize massive data
 Algorithms implemented using hardware
Educational Goals for this Chapter:
 The computer as a tool for
 Communication and Collaboration
 Information Sharing
 Resource Sharing
 Shared Services
Hon Wai Leong, NUS
(UIT2201, Networks) Page 2
Copyright © 2007 by Leong Hon Wai
Introduction to Computer Network
 What is a Computer Network
 Computers connected together
 Why: Share information and resources
 What kind of information
 data files (pictures, videos, audio), programs
 movies, tv and radio signals
 What kind of services
 a shared printer
 a shared software application
Hon Wai Leong, NUS
(UIT2201, Networks) Page 3
Copyright © 2007 by Leong Hon Wai
Basic Networking Concepts
 A Computer Network
 A set of independent computer systems
 connected by telecommunication links
 Purpose:
 sharing information and resources
 Nodes, hosts, or end systems
 individual computers on a network
Hon Wai Leong, NUS
(UIT2201, Networks) Page 4
Copyright © 2007 by Leong Hon Wai
The Ever-changing Internet
Different colors based on IP address
http://research.lumeta.com/ches/map
What is the Internet?

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
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WWW
Video conferencing
ftp
telnet
Email
Instant messaging
…
What is the Internet?

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
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


WWW
Video conferencing
ftp
telnet
Email
Instant messaging
…
A communication infrastructure
Usefulness is in exchanging information
“On-line interactive communities... will be communities not of
common location, but of common interest.... the total number
of users...will be large enough to support extensive general
purpose [computers]. All of these will be interconnected by
telecommunications channels... [to] constitute a labile network
of networks--ever changing in both content and configuration.”
J. C. R. Licklider
Communicating Via the Internet
How’s the
weather in
Seattle, Mar?
[email protected]
Network
[email protected]
MSN Messenger
A Brief History of the Internet and
the World Wide Web: The Internet
 August 1962: First proposal for building a
computer network
 Made by J. C. R. Licklider of MIT
 ARPANET
 Built by the Advanced Research Projects
Agency (ARPA) in the 1960s
 Grew quickly during the early 1970s
Hon Wai Leong, NUS
(UIT2201, Networks) Page 10
Copyright © 2007 by Leong Hon Wai
The Internet (continued)
 NSFNet: A national network built by the
National Science Foundation (NSF)
 October 24, 1995: Formal acceptance of the
term Internet
 Internet service providers start offering
Internet access once provided by the
ARPANET and NSFNet
Hon Wai Leong, NUS
(UIT2201, Networks) Page 11
Copyright © 2007 by Leong Hon Wai
ARPANET, 1980
http://mappa.mundi.net/maps/maps_001/
Figure 7.20
State of Networking in the Late 1980s
Hon Wai Leong, NUS
(UIT2201, Networks) Page 13
Copyright © 2007 by Leong Hon Wai
The World Wide Web
 Development completed in May 1991
 Designed and built by Tim Berners-Lee
 Components
 Hypertext
A collection of documents interconnected by
pointers called links
 URL (Uniform Resource Locator)
The worldwide identification of a Web page located
on a specific host computer
Hon Wai Leong, NUS
(UIT2201, Networks) Page 14
Copyright © 2007 by Leong Hon Wai
History of the Internet

Tim Berners-Lee at CERN in 1989
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Proposal for WWW in 1990
First web page on November 13, 1990
Hypertext - Text that contains links to other text.

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Ted Nelson’s Xanadu
Vannevar Bush’s Memex
(http://www.theatlantic.com/unbound/flashbks/computer/bushf.htm)

W3C
Get more info at:
http://www.isoc.org/internet/history/
History of the Internet
Internet Hosts
100,000,000
10,000,000
Stage 1
DARPA
Experiment,
operation
Stage 2
Enterprise
Internets,
R&A scaling
Stage 3
Universality
1995-NSFNet ceases,
non-USA nets >50%
1,000,000
100,000
10,000
 Kahn poses internet challenge 2Q 73
 Cerf-Kahn sketch gateway and TCP
in 2Q 1973
 Cerf-Kahn paper published May 1974
 Cerf team full spec - Dec 1974
1992-Internet Society
created ceases
1990-ARPANet
1989-first public commercial
Internets created
1986-NSFNet created
1,000
1984-DNS created, DARPA divests
JanInternet
1983-ARPANet adopts TCP/IP, CSNet
100
10
1
1968
created, first real Internet begins
ARPANet
1973
1979
1981-Bitnet created
1984
1990
1995
2001
copyright © 1995 A.M.Rutkowski & Internet Society
Babel

Internet consists of
many different types of
networks

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Ethernet
Token ring
Different types of
operating systems and
other software
How do they work
together?

How’s the
weather in
Seattle, Mar?
[email protected]
Ethernet
Network
Tokenring
Standards
MSN Messenger
[email protected]
The Basic Communication Link
 Dial-up telephone line,
 A circuit is temporarily established
between caller and callee
 Analog medium (analog signals)
 Requires modem at both ends to transmit
information produced by a computer
Computer produces digital information
Hon Wai Leong, NUS
(UIT2201, Networks) Page 18
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Analog vs Digital Signals
Figure 7.1
Two Forms of Information Representation
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(UIT2201, Networks) Page 19
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Analog  Digital Conversion
Figure 7.2:
Modulation of a Carrier to Encode Binary Information
Hon Wai Leong, NUS
(UIT2201, Networks) Page 20
Copyright © 2007 by Leong Hon Wai
The Communication Link (cont…)
 Dial-up phone links
 Transmission rate: 56 Kbps
 Broadband
 Transmission rate: > 256 Kbps
Home Use:
* DSL
* Cable modem
Hon Wai Leong, NUS
Office & Commercial Use:
* Ethernet
* Fast Ethernet
* Gigabit Ethernet
(UIT2201, Networks) Page 21
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Comparison of Transmission Speed
Figure 7.3: Transmission Time of an Image
at Different Transmission Speeds
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(UIT2201, Networks) Page 22
Copyright © 2007 by Leong Hon Wai
Communication Links (continued)
 Wireless Data Communication
 Uses radio-wave, microwave, infrared
 Enables “mobile computing”
 Two types:
 Wireless Local Access Network
 Wireless Wide-area Access Network
Hon Wai Leong, NUS
(UIT2201, Networks) Page 23
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Local Area Networks
 Local Area Networks (LAN)
 Used to connects computers in a small area
(say, in a building)
 Common LAN topologies
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(UIT2201, Networks) Page 24
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Local Area Networks (cont…)
 Most commonly wired by Ethernet
 Using bus topology
 Two ways to wire-up an Ethernet LAN
Hub
Shared Cable
Hon Wai Leong, NUS
(UIT2201, Networks) Page 25
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Ethernet
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
Bob Metcalfe at Xerox PARC
Used for local area networks (LANs)
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Physically near one another
200 computers within 100 meters
Broadcast medium
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Single wire connects all computers
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Each computer has unique 48-bit MAC address
All computers constantly listen
“Carrier Sense, Multiple Access with Collision Detect”
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Sender waits until wire unused before sending
If hears collision, stops, waits random time, retransmits
Ethernet
Ethernet Variations
Ethernet Properties
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Shared
Distributed (not Centralized)
Insecure
Unpredictable Latency & Bandwidth
But it works!
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Under light load (<30%), appears to be point-topoint
Alternative to Ethernet:
Token Ring
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Alternative introduced by IBM
(1980s)
“Passing the Conch Shell”
Wide Area Networks
 To connect across town, country, ocean
 Dedicated point-to-point lines
 Expensive.
 By major service providers (SP)
 Users buy services from SP
 Uses different protocol:
 Store-and-forward, packet-switched tech.
Hon Wai Leong, NUS
(UIT2201, Networks) Page 31
Copyright © 2007 by Leong Hon Wai
Wide Area Networks
 To connect across town, country, ocean
Figure 7.7: Typical Structure of a Wide Area Network
Hon Wai Leong, NUS
(UIT2201, Networks) Page 32
Copyright © 2007 by Leong Hon Wai
Overall Structure of the Internet
 All real-world networks, including the
Internet, are a mix of LANs and WANs
 Example: A company or a college
 One or more LANs connecting its local
computers
Individual LANs interconnected into a widearea company network
Hon Wai Leong, NUS
(UIT2201, Networks) Page 33
Copyright © 2007 by Leong Hon Wai
Structure of Large Network
 Large networks contains hybrid…
Figure 7.8(a): Structure of a Typical Company Network
Hon Wai Leong, NUS
(UIT2201, Networks) Page 34
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Figure 7.8(b): Structure of a Network Using an ISP
Hon Wai Leong, NUS
(UIT2201, Networks) Page 35
Copyright © 2007 by Leong Hon Wai
Figure 7.8(c): Hierarchy of Internet Service Providers
Hon Wai Leong, NUS
(UIT2201, Networks) Page 36
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Overall Structure of the Internet (cont…)
 Internet Service Provider (ISP)
 A wide-area network
 Provides a pathway from a specific network
to other networks, or from an individual’s
computer to other networks
 ISPs are hierarchical
 Interconnect to each other in multiple layers
to provide greater geographical coverage
Hon Wai Leong, NUS
(UIT2201, Networks) Page 37
Copyright © 2007 by Leong Hon Wai
Overall Structure of the Internet
 Internet
 A huge interconnected “network of
networks”
 Includes nodes, LANs, WANs, bridges,
routers, and multiple levels of ISPs
 Early 2003
170 million nodes (hosts)
Hundreds of thousands of separate networks
located in over 225 countries
Hon Wai Leong, NUS
(UIT2201, Networks) Page 38
Copyright © 2007 by Leong Hon Wai
Communication Protocols
 A protocol
 A mutually agreed upon set of rules,
conventions, and agreements for the efficient
and orderly exchange of information
 TCP/IP
 The Internet protocol hierarchy
 Governs the operation of the Internet
 Five layers
Hon Wai Leong, NUS
(UIT2201, Networks) Page 39
Copyright © 2007 by Leong Hon Wai
Figure 7.10
The Five-Layer TCP/IP Internet Protocol Hierarchy
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Copyright © 2007 by Leong Hon Wai
Physical Layer
 Protocols govern the exchange of binary
digits across a physical communication
channel
 Goal: Create a bit pipe between two
computers
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Copyright © 2007 by Leong Hon Wai
Data Link Layer
 Protocols carry out
 Error handling
 Framing
 Creates an error-free message pipe
 Composed of two services
 Layer 2a: Medium access control
 Layer 2b: Logical link control
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(UIT2201, Networks) Page 42
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Data Link Layer (continued)
 Medium access control protocols
 Determine how to arbitrate ownership of a
shared line when multiple nodes want to
send at the same time
 Logical link control protocols
 Ensure that a message traveling across a
channel from source to destination arrives
correctly
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(UIT2201, Networks) Page 43
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Network Layer
 Delivers a message from the site where it
was created to its ultimate destination
 Critical responsibilities
 Create a universal addressing scheme for all
network nodes
 Deliver messages between any two nodes in
the network
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Network Layer (continued)
 Provides a true network delivery service
 Messages are delivered between any two
nodes in the network, regardless of where
they are located
 IP (Internet Protocol) layer
 Network layer in the Internet
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Transport Layer
 Provides a high-quality, error-free, order-
preserving, end-to-end delivery service
 TCP (Transport Control Protocol)
 Primary transport protocol on the Internet
 Requires the source and destination
programs to initially establish a connection
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Figure 7.15: Logical View of a TCP Connection
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Application Layer
 Implements the end-user services provided
by a network
 There are many application protocols
 HTTP
 SMTP
 POP3
 IMAP
 FTP
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(UIT2201, Networks) Page 48
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Figure 7.16:
Some Popular Application Protocols on the Internet
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Application Layer (continued)
 Uniform Resource Locator (URL)
 A symbolic string that identifies a Web page
 Form
protocol://host address/page
 The most common Web page format is
hypertext information
Accessed using the HTTP protocol
Hon Wai Leong, NUS
(UIT2201, Networks) Page 50
Copyright © 2007 by Leong Hon Wai
Network Services and Benefits
 Services offered by computer networks
 Electronic mail (email)
 Bulletin boards
 News groups
 Chat rooms
 Resource sharing
Physical resources
Logical resources
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Network Services and Benefits …
 Services offered by computer networks
 Client-server computing
 Information sharing
 Information utility
 Electronic commerce (e-commerce)
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(UIT2201, Networks) Page 52
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WWW and Hypertext documents
Figure 7.21
Hypertext Documents
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WWW – web-pages
 Web-pages are documents
 similar to any other document, but
 written in special “web-languages”
html (hypertext markup language)
xml
(extensible markup language)
 Allows text, pictures, formatting, etc
 More sophisticated web-pages
 Dynamic pages (dhtml)
 Allows “programming”
Pages with forms, questionnaires, etc
Languages: cgi, perl, jsp, asp, etc…
Hon Wai Leong, NUS
(UIT2201, Networks) Page 54
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WWW – continued…
 Tools for Creating Web-Pages
 Back to basics (eg: UIT2201 pages)
 Frontpage, Dreamweaver, etc, etc
 Web-Sites
 Individual Servers
 Web-Hosting Servers
 Web Applications
 Forms, registration, etc
 ASP (Application Service Providers)
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(UIT2201, Networks) Page 55
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Summary
 Computer network: A set of independent
computer systems connected by
telecommunication links
 Options for transmitting data on a network:
Dial-up telephone lines, DSL, cable modem,
Ethernet, Fast Ethernet
 Types of networks: Local area network
(LAN) and wide area network (WAN)
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(UIT2201, Networks) Page 56
Copyright © 2007 by Leong Hon Wai
Summary (continued)
 The Internet is a huge interconnected
"network of networks"
 TCP/IP is the Internet protocol hierarchy,
composed of five layers: physical, data link,
network, transport, and application
 The World Wide Web is an information
system based on the concept of hypertext
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(UIT2201, Networks) Page 57
Copyright © 2007 by Leong Hon Wai
Thank you.
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(UIT2201, Networks) Page 58
Copyright © 2007 by Leong Hon Wai