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Chapter 13
The Internet
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OBJECTIVES
After reading this chapter, the reader should
be able to:
Know how the Internet began.
Understand the architecture of today’s Internet and its relationship with ISPs.
Understand the importance of the TCP/IP protocol suite.
Understand the role of IP, UDP, and TCP in the Internet.
Understand the difference between the Internet, an intranet,
and an extranet.
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13.1
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HISTORY
AND
ADMINISTRATION
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History
mid 1960s mainframe computers in research were stand alone
Advanced Research Projects Agency (ARPA) in DOD got
interested in connecting computers
In 1967 at an ACM conference, ARPA presented ideas of the
ARPANET.
The idea of Interface Message Processor was conceived, where
Each host computer would be attached to this specialized computer
In 1969, the ARPANET was a reality- with four nodes, UCLA,
UCSB, Stanford Research Institute, University of Utah. Software
used was called Network Control Protocol (NCP).
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History
1972, Vint Cerf and Bob Khan both who were part of the
ARPNET group collaborated on what was the Internetting
Project.
They linked different host on one network.
Ran into obvious problems, e.g. packet sizes, interfaces, diverse
transmission rates, unreliability etc.
In 1973 Cerf and Khan’ landmark paper outlined protocols for
end-to-end delivery of packets. This was new version of the NCP.
The new NCP included TCP concepts such as encapsulation, the
datagram and function of the gateway.
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History
The idea of Error detection and correction was conceived.
1973 The ARPANET project was handed over to the Defence
Communication Agency (DCA).
1977 an internet consisting of three different network
ARPANET, packet radio, and packet satellite was demonstrated.
Shortly there TCP was split into two protocols, TCP and IP.
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History
UNIX was modified in 1981, under DARPA contract and UC
Berkeley to include TCP/IP.
Working code of Berkeley UNIX was given to every
manufacturer, as a base to build products upon.
1983 all other ARPANET protocols were abolished, only TCP/IP
was the official protocol of the ARPANET.
Internet now is not a simple hierarchical structure, it is made up
of many WAN and LANs. Internet is run by companies not the
government.
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Commonly Used Operating
Systems
• The UNIX operating system was created at
AT&T Bell Labs in the early 1970s by Ken
Thompson and Dennis Ritchie
• The first version of the Disk Operating
System (DOS) for IBM personal computers
was created in about 1980 by Microsoft
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Commonly Used Operating
Systems
• In 1984 Apple Computer introduced the
Macintosh, which integrated the operating
system and the graphical interface
• In August 1995 Microsoft introduced the
Windows 95 operating system, which
integrated a copy of DOS and a copy of
Windows
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Linux Arrives
• In 1991 Linus Torvalds decided to create a
UNIX-like operating system kernel for his
IBM-compatible PC as a school project
• Torvalds solicited help via the Internet
• Hundreds of programmers around the world
were working together to create a new Linux
kernel
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The Linux Software License
• A software license is a legal definition
of who can use a piece of software and
how it can be used
• Torvalds decided to base the software
license for the Linux kernel on a model
created by Richard Stallman and the
Free Software Foundation
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The Free Software Foundation and
the GNU Project
• In 1983 Richard Stallman at the Massachusetts
Institute of Technology founded an
organization called the Free Software
Foundation (FSF)
• With the GNU project, Stallman intended to
create a completely free version of UNIX,
written from scratch
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The Free Software Foundation and
the GNU Project
• Hundreds of software programs as part of the
GNU project are included with the Linux
kernel in each copy of a complete Linux
operating system
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The GNU General Public License
(GPL)
• The General Public License (GPL) requires
that source code be distributed with each copy
of the Linux kernel
– The source code is the set of human-readable
programming instructions used to create the
program
• Anyone who obtains a copy of the software
can redistribute it in any form
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The GNU General Public License
(GPL)
Anyone who obtains a copy of the software can
redistribute it in any form
• Anyone can modify the software, the
modifications are automatically subject to the
GPL
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How Linux Is Developed
• Linux kernel development follows the
model of most free software projects
• A person identifies a need and begins
writing a program
• The software developer announces the
project on the Internet
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How Linux Is Developed
• Developers who share an interest in that
project respond, and soon they begin to
work together on different parts of the
project
• The project lead releases the software
(including source code) on the Internet to
try it and fix the bugs
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Note:
RFCs can be found at
http://www.rfc-editor.org
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Figure 13-1
Internet today
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Technical Focus:
Maturity Levels of an RFC
An RFC, during its lifetime, falls into one of six maturity levels:
proposed standard, draft standard, Internet standard, historic,
experimental, and informational.
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Figure 13-2
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Internet administration
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13.2
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TCP/IP
PROTOCOL
SUITE
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Figure 13-3
TCP/IP protocol suite
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Figure 13-4
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IP datagram
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Technical Focus:
Inside the Header of an IP Datagram
An IP datagram contains several fields. The most important
are the source and destination addresses of the datagram (IP
addresses). The header also contains fields related to
fragmentation. The size of a datagram may be too large for
some LAN or WAN protocols. In this case, the datagram is
divided into fragments; each fragment carries the same
identification number as well as other information to help the
receiver assemble the datagram. The header also has two
length fields; one defines the length of the header, the other
defines the length of the entire packet. One field that can
decrease traffic on the Internet holds the number of routers a
packet can visit before it is discarded. The header also contains
a checksum field to determine the validity of the packet.
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Figure 13-5
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Internet address
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Technical Focus:
Classful versus Classless Addressing
With more and more organizations wanting to use the
Internet, the Internet authorities are running out of IP
addresses. Internet addresses were originally designed as
classful addresses. By this, we mean that the total number of
32-bit addresses was divided unevenly into five classes: A, B,
C, D, and E. Class A and B contain blocks of addresses with a
very large range. Each block is granted to one organization,
but most of these organizations never use their allotted
number of addresses. This is a tremendous waste of addresses.
Recently, a new design called classless addressing has been
implemented. In this design, all available addresses are put
into a big pool; each organization is granted a range of
addresses according to its need.
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Figure 13-6
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A part of the Internet
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Figure 13-7
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UDP user datagram
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Technical Focus:
Inside a UDP header
The header of the UDP datagram is very simple: it contains
only four fields. One field defines the application program
that has sent the packet (the source), and another defines the
application program that is to receive the packet (the
destination). Another field defines the length of the entire
packet. The last field carries a checksum for error detection.
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Figure 13-8
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TCP segment format
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Technical Focus:
Inside a TCP Segment Header
The header of a segment is very complicated and contains
optional as well as mandatory fields. We briefly discuss
just the required fields. One pair of fields defines the
source and destination application programs. Another
pair is used for error and flow control; one holds the
unique sequence number, and the other holds the
acknowledgment number. One field defines the size of the
sliding window in the transport layer. The sliding window
in the transport layer uses the same concept as the one in
the data link layer (see Chapter 5). There are also flags
that define the purpose of the segment (for connection
establishment, for termination, for acknowledgment, and
so on). The last required field carries a checksum for
error detection.
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13.3
NEXT
GENERATION
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13.3
ACCESS TO THE
INTERNET
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13.5
PRIVATE NETWORKS:
INTRANET AND
EXTRANET
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Technical Focus:
Network Address Translation (NAT)
A technology that is related to private networks is network address
translation (NAT). The technology allows a site to use a set of
private addresses for internal communication and a set of (at least
one) global Internet addresses for communication with other sites.
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