Prepared by: Saatchi, Seyed Mohsen1 Arab Open University - AOU T171 You, Your Computer and the Net:...

Prepared by: Saatchi, Seyed Mohsen 1

Arab Open University - AOU

T171You, Your Computer and the Net:

Learning and living in the information age

Session 7

Section 4 & 5


From ARPANET to the Internet

Module 2 - Section 4

Book reference: ‘A brief history of the future’, Chapter 10


Arab Open University - AOU

Main ideas covered in this section are:

1. Gateways

2. Transmission Control Protocol (TCP)

3. Internet Protocol (IP)


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


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


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


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?


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


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


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


Anatomy of a packet

Packet Structure:

packet is a string of bits divided into different segments


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


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


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


Anatomy of a packet


Anatomy of a packet

At more detailed level, each header it self has a specific structure, For example:

1- The TCP header


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


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


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



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



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



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



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



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


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

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

TCP/IP stack layers look like the following


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


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


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


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


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


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


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


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


Mass networking and its culture

Module 2 – Section 5

Book reference: ‘A brief history of the future’,

Chapters 11,12 and 13


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


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


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



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



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



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 systemb- C language is allowing UNIX to be Portable



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)



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)



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



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



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



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


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.


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.


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


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


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



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



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



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)



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



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



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


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



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 non-Microsoft software that happened to be available



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)



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



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

Prepared by: Saatchi, Seyed Mohsen1 Arab Open University - AOU T171 You, Your Computer and the Net:...

Documents

Transcript of Prepared by: Saatchi, Seyed Mohsen1 Arab Open University - AOU T171 You, Your Computer and the Net:...