Download The Internet and the World Wide Web

The Internet and the
World Wide Web
ICS 61– Winter, 2015
Why computers?
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Arithmetic
Replicate human thinking
Store and retrieve information
Control other hardware
Communicate
Entertain
Educate
J. C. R. Licklider
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Man-Computer Symbiosis, 1960:
The hope is that, in not too many years,
human brains and computing machines
will be coupled together very tightly, and
that the resulting partnership will think as
no human brain has ever thought and
process data in a way not approached
by the information-handling machines
we know today.
The “Galactic Network”
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Licklider’s 1962 concept of a global computer
network.
Also in 1962, Licklider became the first head
of computer research at DARPA.
2 Types of networks
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Circuit switching
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Path decided on before data transmission starts
Dedicated circuit (e.g. actual copper wire in early
telephony)
Packet switching
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Break message into small chunks (“packets”)
Each chunk has a destination address inside
Each chunk may take a different path from source
to destination
Leonard Kleinrock
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Proposed packet switching in
1960.
His computer at UCLA became
the first node on the Internet in
September, 1969.
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SRI
UCSB
Utah
Then called “Arpanet.”
What do the packets look like?
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Current system, called TCP/IP, was adopted
by the Internet in 1983.
IP: Internet Protocol
TCP: Transmission Control Protocol
The IP Address
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32 bits, written as four eight-bit (0-255)
numbers
128.195.4.228 http://whatismyipaddress.com/
Originally, the first 8 bits specified the
network, and the remaining 24 bits
designated the computer on that network
New version of IP (v6) has 64 bit addresses
http://www.nytimes.com/2011/02/15/technology/15internet.html?
scp=1&sq=internet%20addresses&st=cse
Why Protocols are necessary
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Big-endian v. little-endian
Little-endian: later digits more significant
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Intel x86 architecture
Irvine CA USA
Big-endian: earlier digits more significant
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Motorola processors
thirty two
Why Protocols are necessary
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Big-endian v. little-endian
Little-endian: later digits more significant
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Big-endian: earlier digits more significant
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Intel x86 architecture
Irvine CA USA
Motorola processors
thirty two
Blefuscu v. Lilliput in Gulliver’s Travels, 1726
The IP Packet
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IP Version number
Total length of packet
Source IP Address
Destination IP Addr.
Time To Live (TTL)
Checksum
Data being transmitted (000110100100101…)
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No guarantee packets arrive, or arrive in order.
TCP
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Provides a “virtual circuit” between two
computers. Defines a port HTTP: 80, IRC 194)
Guarantees reliable and in-order delivery of
packets.
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TCP packets have sequence numbers.
TCP programs at each end acknowledge packets
and resend if necessary.
TCP practices congestion avoidance and
provides error checking.
TCP/IP packet
UDP
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User Datagram Protocol
“Lightweight” when compared to TCP,
doesn’t provide reliability or ordering.
Same port facilities, provides error checking.
Better for many time-sensitive purposes.
Used for games, VoIP, IPTV.
The Layers of the Network
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Application Layer (FTP, HTTP, IMAP)
Transport Layer (TCP, UDP)
Network Layer (IP)
Data Link Layer (802.11, Ethernet, WiMax)
Physical Layer (Modems, Coax, Ethernet)
The World Wide Web
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Tim Berners-Lee, 1989 - 1991
“Any network-accessible information could be
referred to by a single ‘Universal Document
Identifier.’”
More conventions, languages, and protocols:
URL, HTML, HTTP
Mosaic (from NCSA), 1993-1995
Client-server architecture
Uniform Resource Locator
More URL
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scheme://[user:password@]domain:port/path
?query_string#fragment_id
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scheme: how to connect, e.g. https
domain: where to connect
port: optional (if omitted, determined by scheme)
path, etc: what to ask for
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query string: info for program, e.g.
q=The+Stanley+Parable
fragment: position in document
encodings: %2D = - %24 = $ %20, + = space
Peer to Peer Architecture
Each
computer is
connected
every other
computer.
Client-Server Architecture
Client:
• Rendering
• Sound
• Some rules
• Some physics
Server:
• Game State
• All rules
• All physics
• All AI