Transcript What is the Internet? - NUS School of Computing

Networks, Internet & WWW
 Reading Materials:
 Ch 7 of [SG3]
 Additional Notes: (from web-site)
 Contents:
 Motivation for Networks
 Types of Networks and Their Structure
 Communication Protocols – routing info
 Network Services / Applications
 Internet and WWW
Hon Wai Leong, NUS
(UIT2201, Networks) Page 1
Copyright © 2007 by Leong Hon Wai
Objectives
In this chapter, you will learn about
 Basic networking concepts
 Communication protocols
 Network services and benefits
 A brief history of the Internet and the
WWW
Hon Wai Leong, NUS
(UIT2201, Networks) Page 2
Copyright © 2007 by Leong Hon Wai
Outline
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What is the Internet?
Where did it come from?
What are we going to discuss in cs193i?
Break
Networking basics
Physical Infrastructure
The Ever-changing Internet
Different colors based on IP address
http://research.lumeta.com/ches/map
What is the Internet?
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WWW
Video conferencing
ftp
telnet
Email
Instant messaging
…
What is the Internet?
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WWW
Video conferencing
ftp
telnet
Email
Instant messaging
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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
Where Did It Come From?
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It was invented by Al Gore. JUST KIDDING!
Early 1960’s - DARPA (ARPA in 1960’s) project headed
by Licklider
Late 1960’s - ARPANET & research on packet switching
by Roberts
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First node installed by BBN at UCLA in September 1969
1969 - Four host computers (UCLA, SRI, UCSB, University of
Utah)
Get more info at:
http://www.isoc.org/internet/history/
http://www.packet.cc/internet.html
ARPANET, 1980
http://mappa.mundi.net/maps/maps_001/
History of the Internet
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1969 - RFCs begun by S. Crocker (http://rfc.sunsite.dk/)
1972 - Email by Ray Tomlinson & Larry Roberts
1970’s - TCP by Vint Cerf & Bob Kahn
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1980s – Hardware Explosion (LANs, PCs, and
workstations)
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Evolved into TCP/IP, and UDP
1983 – Ethernet by Metcalfe
DNS – Distributed and scalable mechanism for resolving
host names into IP addresses
UC Berkeley implements TCP/IP into Unix BSD
1985 – Internet used by researchers and developers
History of the Internet
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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)
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W3C
Get more info at:
http://www.isoc.org/internet/history/
Communicating Via the Internet
How’s the
weather in
Seattle, Mar?
[email protected]
Network
[email protected]
MSN Messenger
Bits and Bytes
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Computer Data is stored in Binary
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Binary Digits (bits) Base 2 representation
1011100001101010
Every 8 bits == 1 Byte
10111000 01101010 (2 bytes (once known as octet))
Hexadecimal == Base 16 representation
1011 1000 0110 1010
B
8
6
A
Decimal == Base 10 (we have 10 fingers)
0...9, A = 10, B= 11, C = 12, D = 13, E = 14, F = 15
Bits and Bytes
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Kilobyte (2^10=1024 Bytes, 10^3=1000 Bytes in
networking)
Megabyte (2^20 Bytes, 10^6 in Networking)
Gigabyte (2^30 Bytes, 10^9 in Networking)
Terabyte (2^40, 10^12)
Petabyte (2^50, 10^15)
Performance: Latency and
Bandwidth
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Latency
How long minimum communication takes in seconds (s)
 Round trip vs. single trip
 More difficult to overcome than bandwidth
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Bandwidth
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Number of bits per time unit usually seconds (bps)
bandwidth
link
latency
Any-to-Any Communication
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n2 Network Effect (Metcalfe’s Law)
Total utility of system proportional to n2
 Think about Orkut, MSN Messenger
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Babel
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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?
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How’s the
weather in
Seattle, Mar?
[email protected]
Ethernet
Network
Tokenring
Standards
MSN Messenger
[email protected]
Divide Work into Layers
Application
HTTP, SMTP, FTP,
TELNET, DNS
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End-to-End
TCP, UDP
Network
IP
Link Level
Ethernet, token ring
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0 1 0 1 0
01010
make network simple and reliable
a
connect segments, address (locating points
on graph) and route (navigating graph)
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01010
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01010
physically encode bits on “wire”
b
Sending Data Along Wires
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Connection-oriented
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Circuit switched
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Persistent connection set up between sender and receiver
Example: telephone system
Connectionless
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Packet switched
Data partitioned into packets and H Data
sent individually from sender to receiver
 Reassembled at receiver
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Message
H Data
H Data
H Data
Comparison of Switching
Technologies
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Circuit switched
Advantages
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Only route once
Latency and bandwidth
constant
Disadvantages
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Idle resources unavailable
for other connections
Large setup time
Single point of failure
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Distributed state
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Packet switched
Advantages
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Efficient use of wires
Small startup overhead
Disadvantages
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Route each packet
Per packet overhead
Bursty
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”
Thank you.
Hon Wai Leong, NUS
(UIT2201, Networks) Page 26
Copyright © 2007 by Leong Hon Wai