Transcript Lecture 8 - OoCities

Arab Open University - AOU
T171
You, Your Computer and the Net:
Learning and living in the information age
Session 7
Section 4 & 5
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From ARPANET to the Internet
Module 2 - Section 4
Book reference: ‘A brief history of the future’, Chapter 10
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Arab Open University - AOU
Main ideas covered in this section are:
Gateways
2. Transmission Control Protocol (TCP)
3. Internet Protocol (IP)
1.
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Introduction


Although the host computers connected to the
ARAPNET were diverse, the actual network itself –
that is the subnet of IMPs - was highly homogenous
 The IMPs were identical
 Run the same software
 This had made the process of monitoring,
controlling and rebooting them from a control
room is possible and easy
The Internet is highly diverse and heterogeneous
 Links all kinds of different networks into one
apparently seamless whole
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Introduction
 This section covers the story of how the transition was made
from the homogenous ARPANET to the heterogonous
Internet?
 The key was a new set of protocols,mainly
 TCP- Transmission Control Protocol
 IP- Internet Protocol
 Generally referred to as TCP/IP
 Because they (TCP,IP) highly linked together
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Casting the Net

Beside ARPANET, several other packet-switched networks
(systems) started operating




The British NPL network (set up by Donald Davies)
Cyclades network in France
ALOHA packet-radio network in Hawaii
The satellite network SATNET
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Casting the Net

Although they were all packet-switched networks
1 - They were incompatible:
Using different platforms.
2 - There was a serious problem in connecting these networks together:
How to let them communicate and interact together, and comprehend
each others?
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Casting the Net

Vint Cerf had come up with a good solution to solve this problem,
and connect those incompatible networks:

1- Using computers known as Gateways ( later known as
Routers) between different networks

2- Making hosts responsible for end-to-end transmission of
packets, together with error correction and retransmission if
necessary

3- Devising the protocols necessary for performing the
previous two tasks
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Casting the Net

The required protocols were
 TCP
 IP
 Were developed by Vint Cerf and Robert Kahn

The critical feature of TCP/IP was its open architecture
 Allowed the linking of any network to the rest of the networks
via a gateway computer.

TCP/IP enabled the huge growth of network connectivity  to the
Internet
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Anatomy of a packet

Long messages are broken into smaller, equal-sized chunks
called packets


Switched through routers until they reach their destinations
Software associated with the TCP/IP family of protocols takes
care of the assembly, disassembly and addressing of packets
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Anatomy of a packet
Packet Structure:

packet is a string of bits divided into different segments
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Anatomy of a packet

Those segments could be classified as follows:

Headers (depend on the layers’ protocols)
 Application layer’s header
 Transport layer’s header
 Network layer’s header
 Source IP address
 Destination IP address
 Total length of the packet
 Time to live(time allowed for the packet to persist in
the internet before being discarded by a router or host)
 Link layer’s header

Payload or the data segment
 It is the core (chunk of the original message)

Trailer
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Anatomy of a packet

So in order to allow the payload (data segment) to pass through
the Internet


Extra information are added to it in a form of headers and
trailer
Each layer in the stack adds its own header to an outgoing packet
and strips off (removes) the appropriate layer’s header from
incoming packet
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Anatomy of a packet

In the case of the packet illustrated in the diagram, for example,
there are 4 layers of header. Reading from left to right the might
correspond to the headers added by




1- An e-mail application (SMTP)
 Simple Mail Transfer Protocol
2- TCP
3- IP
4- Ethernet
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Anatomy of a packet
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Anatomy of a packet

At more detailed level,
each header it self has a
specific structure, For
example:

1- The TCP header
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Anatomy of a packet

2- The IP header

May contain the following
information

Some miscellaneous
information related to IP




E.g., version
The Internet address of the
sending machine
The Internet address of the
destination machine
Time to live

To specify how long (in
seconds) a packet is allowed to
persist in the Internet before
being discarded by a router or
a host
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Anatomy of a packet

Note!

The protocols which underpin the Net have to
specify things at a very detailed level

But once they are agreed and tested, they
can then become effectively invisible to us,
the users, because computers handle them
effortlessly in the background
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TCP/IP and your computer

Any computer connected to the Internet has to ‘speak’ the
language of the network’s protocols

TCP/IP family of protocols (software) should be installed into the
computer for accessing information (browsing)



TCP/IP lunched when you initiated a dial-up connection
In the early days of the Net, TCP/IP software had to be
obtained separately or written specially for the operating
system of a specific machine
But nowadays, it comes with the operating system
 Windows, Unix, Linux, and Apple Mac
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TCP/IP and your computer


The original version of TCP protocol was joining both TCP and IP
features
It was then split into two protocols
 TCP : To deal with their assembly and disassembly
 IP
: To handle packet addressing
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TCP/IP and your computer

The design philosophy behind this was the belief that it was better
to have many specialized protocols


Each did one job
They co-operated with each others

Rather than having one monolithic protocol
 That tried to do everything
 hard to be controlled and modified

This is called the modular design
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TCP/IP and your computer

Some Internet protocols used by your computer are




Hypertext Transfer Protocol (HTTP)
 Allows you to get pages from Internet, and to
communicate with the web (i.e. WWW) in general
Simple Mail Transfer Protocol (SMTP)
 Used for sending and receiving e-mail
Point-to-point protocol (PPP)
 Governs the transmission of IP packets over serial lines
like the one running from a user modem to ISP’s modem
Others
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TCP/IP and your computer

These protocols are designed and operated using layered
approach
 Layered model of communications

Each layer performs a specified Job and cooperates with the
next layer

Packets travel vertically up and down through the layers

The protocols at each layer process the packets

Pass them to the next layer / protocol
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TCP/IP and your computer

For this reason, the TCP/IP software running on your
computer is called TCP/IP stack

When you’re communicating with the Net, packets are
going up and down through the stack
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TCP/IP stack layers look like the following
Layer
Function
Protocols used
Application
Deals with applications programs used by the
end-user. The protocols which reside at this
level are embedded in the particular
applications programs you use.
SMTP, HTTP, FTP, Telnet
Transport
Deals with the disassembly and reassembly
of packets, error detection and correction,
etc.(i.e. the reliability and integrity of
messages).
TCP
Network
Deals with the addressing of packets (i.e.
figuring out how to get packets to their
destination). It gives no guarantees about
whether packets will get through, it just
decides where they will be sent.
IP
Link
Responsible for communicating with the
hardware which connects your machine to the
Net (e.g. the Ethernet card which connects
you to the LAN and via a router to the Net, or
the modem If you are using dial-up access).
PPP
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How a stack works?

TCP/IP stack works by passing packets up and down from layer
to layer

Each protocol layer does something to the packet in order to
achieve its purpose

For example
 Each protocol layer in the stack adds its own header to an
outgoing packet and strips off its own header from an
incoming packet
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How a stack works?

The link layer (bottom layer)



The lower layer
Responsible for communicating with the hardware which
connects your machine to the Internet
It can be an Ethernet card
 Connects you to a local area network (LAN) and via a
router to the Internet
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How a stack works?

In case of dial-up access
the hardware is the modem which connects you to the
Internet via an ISP (Internet Service Provider).
Example:
 Point-to-Point Protocol (PPP)
For an incoming packet:
 The link layer takes packets from the network wire (Local Area
Network or modem)
 Removes any link layer header information (e.g., Ethernet
information)
 Pass them to the network layer



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How a stack works?

The Network layer



Deals with addressing of the packets
 IP resides
 Responsible for figuring out how to get packets to their
destination
It gives no guarantees about whether packets will get through
or not
It just decides where they will be sent
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How a stack works?

Example:
 Internet Protocol (IP)

For an incoming packet:
 Checks whether the packet is corrupted or not
 If it is, discards it
 If it is OK
 It strips away any network layer header information
 Passes it to the Transport Layer
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How a stack works?

The Transport Layer



TCP resides
Deals with the disassembly and reassembly of packets, error
detection and correction, etc
 It ensures the reliability and integrity of messages
Process them to and from the application layer above
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How a stack works?

Example:
 Transmission Control Protocol (TCP)

For an incoming packet:
 Checks to see if the packets have arrived in the order which
they were sent (appropriate order of the packets)
 Reassembles them in the correct order, if they were
unordered
 If a packet is missing
 E.g., because IP has rejected it as corrupted
 It requests a retransmission
 When the complete assembled packets is obtained, TCP
passes them up to the Application layer
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How a stack works?

The application layer


At the top of the stack
This is where the user interact with the network


Deals with application programs used by the end-user
The protocols which reside at this level are:




SMTP: embedded in the particular application program you use
to send and receive e-mail
Telnet: embedded in the particular application program you use
to login to a remote machine
FTP: embedded in the particular application program you use to
transfer files
HTTP: embedded in the particular application program you use
to browse web pages
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Mass networking and its culture
Module 2 – Section 5
Book reference: ‘A brief history of the future’,
Chapters 11,12 and 13
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Introduction

Users of the original ARPANET/ Internet were mainly the
scientists and researchers (little social and political discussions)


They were not open for the public
However, the number of Internet users today is extremely large
 Almost everyone can have access to the Net
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Introduction

Some of the factors that led to this critical change in
the nature of the Net were:

Usenet news



Because it brought to networking large groups of people
who felt that the proper function of the Net was to argue,
discuss and enthuse about all topics that people
interested in  The global system of discussion groups
Usenet emerged from the community of researchers and
programmers who used the UNIX operating system
Fidonet


Network was built by hobbyists and enthusiasts
An alternative to the Net
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Growth of alternative networks

So the Usenet news was a way of exchanging news and
opinions among large number of people

It was emerged from the community of researchers and
programmers who used the Unix Operating System

Unix is a Multi-user time sharing operating system

A Multi-user operating system allows more than one user to
work on the machine at the same time

A time-sharing system is a system that shares the CPU
time among the users of the machine
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Growth of alternative networks

Unix was created at Bell Labs
The central research and development facility of AT&T company
It was written by Ken Thompson and Denis Ritchie
 Denis Ritchie is the inventor of C language
In 1974, AT&T decided to sell Unix for research institutions and
universities for very cheap price
 Moreover, AT&T send the source code (the actual program
written to produce the software) of UNIX with a license to change
the source code



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Growth of alternative networks

The Unix operating system spread rapidly among computer
science department around the world

So the main features that distinguished Unix from other
operating system are as follows

1- It was the only powerful OS which could run on the
minicomputers used in most universities

2- the source code was included, and the AT&T license
included the right to alter the source code and share
changes with other licensees
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Growth of alternative networks

One major advantage of UNIX is the existence of Kernel
 An isolated small piece of code that can be easily placed
in another machine, which will then run Unix  Kernel is
the core of OS

Final stages of Unix was written in C language
 It is a high level language, that have the following
advantages


a- Easy to understand and modify (by computer
scientists and also students)
 Made it easy for a programmer to add new function
to the operating system
b- C language is allowing UNIX to be Portable
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Growth of alternative networks

As compared to Assembly language

Low level language

a- Difficult to understand and modify

b- Machine specific

If you have an assembly program running on one
machine, it can’t be used on another machine
with a different architecture (not portable)
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Growth of alternative networks


With the continual extensions and improvements to UNIX being
made by its users, a need arose to incorporate these changes
into updated versions and distribute them to the UNIX
community

So there was a need to be able to exchange new releases
and features of Unix
This need was achieved by developing a new program called
UUCP (Unix-to-Unix copy program)

Enabled users of Unix to import new Unix programs and
releases

As well as exchange some common discussions through a
phone line (this was done for the first time)
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Growth of alternative networks


UUCP leads to the creation of Usenet News

It is a program that enabled people to post articles and
notes to a shared location

It can be read by other people that have access to that
shared location

Very close to nowadays conferencing system
Each shared location was called a Newsgroup

Which people can join based on their Interests
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Growth of alternative networks

Usenet News ‘spin-off’



Its main intention was as a utility device
Used to exchange information about problems and solutions
within the user community
Now, it is used as a ‘never-ending’ world wide conversations
in all the topics
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Growth of alternative networks

Unix and its Usenet News

Was available for universities
 For students and academic staff

And for industrial laboratories and business firms
 For researchers

Available for Minicomputer users, not for PC users
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Growth of alternative networks



PC users seek to create a networking system of their own !
This lead to the creation of Fidonet
 Build by hobbyists and enthusiasts
 It emerged from bulletin board technology as an alternative to
the Net
 It was the first system, that allowed PC home users to receive
and store information
 Then send it to other nodes in the network through phone
lines
This had increased the number of network users so rapidly
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Intellectual Property

Intellectual Property is used to protect the right and companies to
profit from their ideas products and books

Intellectual property includes:




Patents: which is mainly for new inventions
Trade mark: which is used to identify and distinguish products
Design: which is mainly for shape and appearance
Copyright: which includes protection for books, music, fimls and
software.
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Open source

Open source was established by Richard Stallman, its main idea
to have the software and its source code free and available for
programmers to benefit from and improve in a cooperative
manner.

Intellectual property includes:




Patents: which is mainly for new inventions
Trade mark: which is used to identify and distinguish products
Design: which is mainly for shape and appearance
Copyright: which includes protection for books, music, fimls and
software.
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The Open Source



With new, commercial ideas, a tension occurs

whether to to keep them private, for yourself

Or share them with the world
Registering the new product in a patent

Protects it but…

Reveals its details and makes it available for anyone who
cares to examine the applications lodged with the Patent
Office
Not registering the product, in order to keep the design secret

Rather than revealing how it works via a patent

Threatened by the ‘reverse engineering’ process

Secrets will be revealed and might be stolen
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The Open Source


So all of the previous assumes a commercial model – that the
originator of a ‘bright idea’ wants to profit from its exploitation

Its source was hidden and no more open for improvements
and change

This was a shock for the computer research community
The availability of Unix OS with its source code, was a very
important factor in the development of the Internet
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The Open Source movement

For non-commercial products, Open Source movement appeared
 Established by Richard Stallman

It is main idea is to have the software and its source code free
and available for programmers to benefit from and improve in
a cooperative manner

Where an originator is happy for others to closely examine
and suggest improvements to the original concept; where
profit is not a motivating factor but finding more 'elegant'
solutions to a problem is more important
 e.g. the development of the UNIX operating system
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The Open Source movement

Richard Stallman and the Free Software Foundation

1. The discovery that it was software which sold hardware rather
than vice versa further reinforced the notion that the intellectual
property embodied in a program could be exceedingly valuable

2. As software became commercially important, companies
began to copyright their software and keep secret the source
code at its heart

3. This ran counter to the 'cooperative improvement' culture of
the early users of the Internet
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The Open Source movement

4. In reaction to this and in an attempt to preserve the
research culture of openness, Richard Stallman launched
the Free Software Foundation, based on a new 'copy left'
licensing system

Grants to users of a program the right to alter its
source code, provided they pass on the right to alter
the revised code under the same terms
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The Open Source movement

So, open source movement was established with an idea was


To have the software and its source code free and available
for programmers to benefit from and improve in a
cooperative manner
Its main intention

Wasn’t profit

Rather finding solutions to problems, enhancing the product
and coming up with more elegant version

And preserving the research culture of openness (The early
use of Internet)
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The Open Source movement

The UNIX operating system was one of the key pieces of
software at the heart of the development of the Internet, and a
symbol for the practice of constantly making and distributing
improvements to source code

When UNIX became a commercial product and thus subject to
protection from alteration, it sent a shockwave through the
computer research community
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The Open Source movement

The challenge was taken up first by Richard Stallman (again) and
then, with greater long-term success, by Linus Torvalds and
others

Linux is a clear example of Open Source software

Developed by Linus Torvalds

Linux is an alternative operating system based on
cooperative development and the ‘copy left’ principle

It is the PC version of Unix OS

It is one of the best networking operating system
 Available free of charge

Collectively this approach became known as the ‘Open
Source’ movement
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The Open Source movement

In the last few years, the Open Source movement has attracted a
great deal of attention in the computing industry and the media.
The increased visibility of Open Source software is a product of
several factors:

1. The current dominance of Microsoft in the software
market has been challenged by the US Department of
Justice

2. The decision in January 1998 by Netscape to release the
source code of their browser

3. The discovery (by the mass media) of Linux, and its
subsequent adoption in corporate applications

4. Promotion of the benefits and philosophy of the Open
Source movement by influential figures

5. The realization that many key pieces of networking and
web server software are in fact Open Source creations
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Values, theories and facts

Values




Facts are statements that people generally agree to be true
Values are expressions of what they believe to be right, good,
worthwhile, etc
It's possible to have a rational argument about facts, but much
more difficult to have one about values
For example
 Two people might disagree about whether Bach was born
before Beethoven - but both will probably agree that there
is a neutral way of resolving the dispute by consulting a
reference source that both accept as reliable
 But there is no analogous way of resolving a dispute about
whether Beethoven was a better composer than Bach,
because that dispute is really about values, not facts
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Values, theories and facts

Values play a role in discussions about Open Source

There are people, for example, who favor Open
Source software simply because it is not made by
Microsoft

This may be because they believe that it's better than
Microsoft's products, but such is their dislike of the
micro software giant that some would probably
choose an inferior product if it was the only nonMicrosoft software that happened to be available
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Values, theories and facts

Theories


Then there are people whose views about Open
versus Closed Source software are colored by their
theoretical beliefs
For example

Economists tend to be suspicious of market dominance by a
single company because they regard it as an impediment to the
operation of free markets (e.g. it is very difficult for any company
to enter the spreadsheet software development since Microsoft
Excel is a de facto standard)
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Values, theories and facts

Facts

Given that software is an engineering construct, you would
have thought that the easiest disputes to resolve would be
those about the supposed technical superiority of Open
Source software. Surely this at least is an empirical question
that can be settled by experiment?

It is not that simple. In late 1998, an internal Microsoft paper
analyzing the Linux phenomenon was leaked to the Net. The
paper suggested that the company saw Linux as a serious
threat to its Windows NT (now Windows 2000) network
operating system
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Values, theories and facts

However, some experiments to compare NT and Linux were
conducted by some company which shows that windows NT
outperformed Linux

These findings attracted a storm of protest from the Open
Source community. Critics pointed out that the tests were paid
for by Microsoft

However, the company rejected these criticisms  To the
confused observer caught in the crossfire, it is difficult to know
what the facts are
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