Communications

							                                               St Louis

                               History Of Communications

                                          By Gerry_Cornelius

Humans have always felt the need to COMMUNICATE. The history of civilization in many ways
has followed human advances in communication, and today, it is the nations with the most
advanced forms of communication that are the most powerful nations in our world.


                           Part 1: Early forms of communication

1. Symbols and Gestures

One of the forms of communication used by early people was hand signals and gesture. In the
environment they lived in, gestural communication would have been more effective than vocal
communication, under certain circumstances such as hunting.

First, it is silent, so there is little risk of alerting predators or prey to one’s presence.

Second, much of the information to be communicated would be spatial, such as the whereabouts
of dangerous predators, easy prey or carcasses to be scavenged. It may be that pointing was
among the earliest communicative gestures.

 (from The South African Agency For Science and Technology Advancement)
at: http://www.saasta.ac.za/it/communication.html
This interesting Web site also states:

One of the keys to complex, abstract thought is the use of symbols, including geometric shapes.

The African symbol language was a common form of communication throughout Africa. Even
different language and regional groups understood each other's symbols.
However, only the initiated were taught the use and meaning of various symbols and it was
mainly used to record esoteric (secret) information

The use of graphics to communicate information is today a huge industry in which technology
plays a major role, just think of computer graphics and the world of advertising.

When we think about this, we can see many areas where primitive forms of communication have
evolved to become key parts of today's civilisations.

2. Semaphore Flag Signalling System

The idea of GESTURES evolved into a system using hand-held
flags.

This is a VISUAL method.

The Semaphore flag signaling system is an alphabet signalling
system based on the waving of a pair of hand-held flags in a
particular pattern.
The flags are usually square, red and yellow, divided diagonally with the red portion in the upper
hoist.
                                                                      The letter "O" in semaphore.
3. Smoke Signals

From the site by William Tomkins, at:
http://www.inquiry.net/outdoor/native/sign/smoke-signal.htm

Native Americans, as we can see in many Western movies, particularly the early 'stagecoach'
types, used smoke signals to transmit information over long distances.
Tomkins writes:

As the signals were visible to all, unless they had a secretly understood significance they would
be conveying the information alike to friend and enemy. There were, however, certain more or
less recognized abstract smoke signals, of which the following are a few. One puff meant
ATTENTION. Two puffs meant ALL'S WELL. Three puffs of smoke, or three fires in a row,
signifies DANGER, TROUBLE, OR A CALL FOR HELP.

As we can see, smoke signals are another VISUAL method.

4. Heliograph and Signal Lamp

On the right, the picture shows a scene from British
imperial history, the war in Africa against the Zulus.

The HELIOGRAPH is a mirror that reflects sunlight to a
distant location. The mirror is mounted on a tripod to
keep it stable and allow it to be pointed accurately at
the distant location.

The SIGNAL LAMP is used at night, when the sun of
course is not available as a light source.

The message is transmitted using MORSE CODE – a
sequence of 'dots' (short flashes of light) and 'dashes'
(long flashes of light) that represents letters and
numbers.

This is another VISUAL method.

An account on the British Army Web site run by the
Royal Corps of Signals has the following account of the
use of the heliograph in the Zulu war:

http://www.army.mod.uk/royalsignalsmuseum/PostalCovers/Heliograph.htm

"In 1879, Lieutenant General Lord Chelmsford broke the back of the Zulu uprising with the
advance of his three columns into Zululand, taking on the might of the Zulus and defeating them
at Kambula, Gingihiovo and Ulundi.

At one stage of this advance, part of the British force became beleaguered in Fort Ekowe, the
ground between them and the Tugela river being in Zulu hands. At Tugela Lieutenant Haynes,
RE, endeavoured to establish communications with the Fort by heliograph.

This instrument, manufactured in India by the Bengal Sappers and Miners, had an oscillating
mirror aligned to reflect the sun's rays to the distant station. It was operated by using the Morse
code. Haynes persisted, in spite of much discouragement, for a week, before he received an
answer. At the Fort, Major Wynne, RE, had noticed the signal almost immediately and tried to
reply with shaving mirrors, without success.
He spent the week constructing a large screen which pivoted from the horizontal to the vertical,
the time of the vertical appearances producing the elements of the Morse code. Some signal
traffic was passed, and as a result the relief of the force beleaguered in the Fort took place."

5. Talking Drum

From: http://www.talkingdrum.fsnet.co.uk/

When explorer Henry Morton Stanley was travelling
along the Congo river, he was amazed to find that the
villagers invariably knew he was coming in advance of
his arrival.

The source of this conundrum was the talking drum.
Used across Africa as a sort of 'rhythmic telegraph',
the talking drum could send messages from village to
village in the form of pitched drum beats, enabling
communication through dense forest and even across
mountain ranges.

The subtleties of language may be played out on the drum. Different beats, pitches and rhythms
convey layers of message and meaning, providing effective, direct communication whatever the
distance or terrain. This is the concept of the talking drum.

This is an AURAL method of communication (using sound waves)

Obviously, VISUAL methods such as the HELIOGRAPH, SIGNAL
LAMP, and SMOKE SIGNALS were limited to 'line of sight' – in
other words the person receiving the message had to be able to
actually see the person sending the message; while AURAL
methods depended on being able to hear the person sending the
message.
To solve these problems, in the late 1800's new forms of
communication were invented: the telegraph and, later, the
telephone.

EARLY FORMS of ELECTRICAL COMMUNICATION

6. The TELEGRAPH.

The picture (right) commemorates the capture of Bloemfontein
from Boer control by Field Marshal Lord Roberts on 13 March
1900.
see: http://www.army.mod.uk/royalsignalsmuseum/PostalCovers/AutomaticTelegraph.htm

From "The Era Of Morse Telegraphy"
       see: http://www.faradic.net/~gsraven/telegraph_tales/grumbine/grumbine_1.html

                                         ***********

The telegrapher sent Morse code by tapping on a small springloaded brass lever, or key, which
opened and closed an electrical circuit. In time, a more advanced instrument was developed
which made any desired number of dots with one stroke at a higher speed than the conventional
key, but each dash had to still be made separately as before. The telegrapher had to purchase
his own high speed key which became known as a "BUG." He always carried it with him.
The telegrapher was as much a part of the railroad as the ties that supported its rails. Without his
services trains could not have moved safely any faster than horse-drawn coaches.

The original "MORSE CODE" was invented and used by Samuel Morse since the 1840's to allow
letters to be sent as short electrical signals (dots) and long electrical signals (dashes) along with
some embedded spaces was also called the "AMERICAN" MORSE CODE.

This original "Morse Code" was replaced in England in the 1800's by a somewhat similar code
called the "CONTINENTAL" or "INTERNATIONAL" MORSE CODE which became the universal
standard for Radio Telegraph Communications and for European land-line telegraphic
communications.

All railroads, the vast Western Union and Postal Telegraph Companies, news- papers, brokerage
firms, telephone and pipe line companies, and some large manufacturers employed many
telegraph operators. It was a major career with higher than average pay, and numbered into
many thousands of telegraphers. Telegraphy became the SYMBOL OF PROGRESS.

During 1907 ads appeared asking for thousands of students to learn telegraphy.

"20,000 Telegraphers wanted just to fill the extra positions when the new 8-hour law goes into
effect March 1, 1908."

                                           ***********

A: _____    How many people do you think work in this career (telegrapher) today, world-wide?

a) 10 million    b) 1 million     c) 100,000        d) 10,000        e) 1,000          f) none

Actually, the telegraph is still with us, in a slightly different form: The TELEX machine, still used to
transmit messages across the world, looks rather like a typewriter.
Nowadays it is rather obsolete (it only manages about 10 characters per second) but is still used
by shipping companies and banks.

And for those people who like to use old-
fashioned technology, it's even possible to
convert a PC into a telex machine:

"The PcTelex board is an advanced
electronic telex processor, to be built into
your IBM-compatible PC. With this PC
upgrade you can perform all traditional telex
functions - significantly faster and more
economically than with the traditional telex
machine. Your telex message is prepared with your standard word processing program - or
you may use the word processor integrated into the PcTelex program, TelexFax/Win."


                                           ***********

NOTICE that smoke signals, the heliograph, Morse code, and the Telex, were all ways of sending
information based on the presence or absence of a signal:

SMOKE / NO SMOKE (smoke signals)
LIGHT / DARK (heliograph, signal lamp)
DASH / DOT (Morse code)
The TALKING DRUM attempted to reproduce human speech rather than simply transmit 'on or
off' signals. Obviously the drummers could have used the drums to transmit a 'code', like Morse
Code, but they preferred to mimic human speech.

Human speech is an ANALOGUE form of communication. Analogue communication uses a range
of frequencies and transmits a lot of information at the same time. For instance, human speech
has a wide range of frequencies and a wide range of volume, from a whisper to a shout! Human
speech contains emotional information as well as pure data.

When we reduce it to printed words and transmit it via a telegraph, or a heliograph, we lose the
emotional content and retain only the basic data.

It's rather similar to email. If you use email a lot, you probably have experienced a situation where
the 'other' person thinks you're being nasty towards them, even if you didn't intend to be nasty.

This is because emails contain only the DATA – the WORDS – and the emotional information
present in our voice, when we talk to another person, is lost. Sometimes we use 'smiley' icons to
try to replace some of that lost information. 

      The main two types of communication, therefore, are ANALOGUE and DIGITAL.

Examples:

ANALOGUE                                                   DIGITAL

Talking Drum                                               Smoke signals
Speaking face-to-face                                      Heliograph / signal lamp
Telephone                                                  Telegraph (Morse Code)
Radio and TV (one way only – from them to you)             Telex (Telex Code)
7. The Telephone

Soon after the invention of the Telex, came a far more important invention: The Telephone.
Originally the invention of the telephone was credited to Alexander Graham Bell. However, in
2002, the US Congress decided to recognise, instead, Antonio Meucci as the true inventor of the
telephone. However, even today, there are people who won't agree.

Fig. 1

How the simple telephone works

Notice that there are two microphones,
two receivers, and a battery that
supplies electric current.

When the person on the right speaks
into the microphone, the sound waves
make the diaphragm (membrane)
vibrate.

The vibrations are passed to the
carbon grains inside the transmitter
(microphone). This causes a varying resistance, which makes the current passing through the
circuit also vary.

When the varying current passes through the receiver, or earphone, the current is converted back
into varying sound waves, so that the listener (on the left) can understand what the person on the
right is saying.


                                     Part 2:    Switching

The TELEGRAPH was a simple cable connecting two locations. All the early cables ran alongside
the railroads.

When someone wanted to communicate with someone in another town, they would have to go to
the telegraph office and write the message down. Then the telegraph operator would transmit it to
the other town using Morse Code.

The message was received and written down on a piece of paper. Then, a 'telegram boy' would
deliver the message to the correct destination.

You can see that this was rather time-consuming and inconvenient. When the TELEPHONE
arrived, it had some big advantages:

        People could hear emotion in the voice rather than just reading a message.
        A lot more information could be sent by talking rather than writing and reading.
        Above all, people wanted to be able to send and receive messages instantly, rather than
         having to go to a telegraph office.

This gave rise to the next big problem of communications: SWITCHING. How to connect 'any'
telephone to 'any other' telephone?
Two telephones can be connected two ways: A calls B, or B calls A.

                                                    N = 2 (number of 'subscribers')
                                                    C = 2 (number of possible connections)



Three telephones can be connected six ways: A-B, B-A, A-C, C-A, B-C. C-B


                                                                  N=3
                                                                  C=6




Four telephones can be connected twelve ways. N = 4, C = 12.




The total number of ways in which telephones can be interconnected is given by the
formula:

C = N (N-1) where C is the number of possible connections and N = number of phones.

Questions.

Calculate the number of possible interconnections:

_____ 1. 10 telephone users.

_____ 2. 100 telephone users in a small village.

_____ 3. 1000 telephone users in a large village.

_____ 4. 10,000 telephone users in a small town.

_____ 5. 100,000 telephone users in a medium town.

_____ 6. 1,000,000 telephone users in a city.

      Now use EXCEL to make a CHART of the number of possible interconnections versus
       the number of telephones.
Does the number of interconnections increase in a LINEAR form (a straight line graph) or as a
SQUARE LAW (curved graph increasing very rapidly)?

Your answer: ___________________


The first switchboards

These were 'manual' – that is, a person, called
the 'operator', sat in front of the switchboard
(literally, a 'board' full of 'switches') and
connected telephone users as required.

See the diagram on the right, courtesy of
PrivateLine.com, at:
http://www.privateline.com/manual/four.html

Follow the connection from the 'Originator'
to the 'Called Party' and trace it in red ink on
your page.




Women telephone operators using a manual
switchboard in Montrose, Colorado, around 1915.
Courtesy: Denver Public Library.


                                                        Of course, telephones proved to be
                                                        such a popular item, that soon the
                                                        number of phones grew very large.

                                                        It became impossible to continue
                                                        connecting them together by means of
                                                        cords and 'telephone operators'.

                                                        Inventors began to experiment with
                                                        automatic switches to replace the
                                                        operators.




Just like all the telegraph operators had lost their jobs at the turn of the century, when the
telephone superceded the telegraph, so now, most of the telephone operators would lose their
jobs with the arrival of the new switches, which were installed in large buildings known as
'telephone exchanges'.
Automatic Switching

The early operator (manual) switchboards soon became too large and
clumsy, as the number of people wanting telephones increased rapidly.

An engineer called Strowger invented a special type of electromechanical
switch. It had 10 vertical steps and 10 circular steps.

Almon B. Strowger was an undertaker in Kansas City, USA. The story goes
that there was a competing undertaker locally whose wife was an operator
at the local (manual) telephone exchange.

Whenever a caller asked to be put through to Strowger, calls were
deliberately put through to his competitor. This obviously frustrated
Strowger greatly and he set about devising a system for doing away with
the human part of the equation !



                                                                               A Strowger selector
                                                                     capable of selecting 100 lines.


Every time the Strowger switch received a pulse of voltage, it changed one step. So as to be able
to use the switch, the dial telephone was introduced. The dial had 10 (0 – 9) possible numbers,
corresponding to the 10 positions of the Strowger switch.

Picking up a telephone caused the Strowger switch to be energised. If the caller dialled, for
instance, the number 5, then the switch would step vertically to the fifth position.



                              th
After the switch reaches the 5 vertical step, imagine the user dials a 4.         5
                                                                                  4
                                                                                  3
                                                                                  2
                                                                                  1

                                                              th
The Strowger switch now rotates its circular selector on the 5 level,
to the fourth position.

Therefore a single Strowger switch is capable of selecting any one                                     4
of 10 x 10 lines, = 100 lines in total.

If each subscriber were given a single Strowger switch, they would be able to call any one of up
to 100 users – including themselves, so of course they really could call any one of 99 other
telephone users. As the number of subscribers grew, it was necessary to increase the number of
Strowger switches.

                Switch 1           Switch 2       Switch 4         Switch 5

Up to:          100 users          10,000         1000,000         100,000,000

                village            town           city             metropolis
A village might be able to use just two telephone numbers using the above system. A town would
have to use four numbers. A city would use 6 numbers, while a metropolis would use 8 numbers.

As an example, Monterrey once used only 6 telephone numbers. This means that there were less
than 1 million possible subscribers at that time.
Then the number 3 was added. This multiplied the possible number of subscribers by 10, giving a
maximum of 10 million.

Recently another number, 8, was added, increasing the number of possible users once more.
This has probably been necessary due to the enormous increase in cellular phone users and also
because of extra lines installed for Internet use.


Strowger Switches were NOISY!

A recording of the sound of a Strowger switch can be found at the following address:

http://www.seg.co.uk/telecomm/step1.wav

In this recording, a telephone user is dialling the number 958 and we can clearly hear the various
sounds of the stepping and rotating selectors. Now imagine a large telephone exchange building,
where thousands of these Strowger switches are working at the same time. It's necessary to wear
ear protectors because the noise is so loud!


                                                   ***

                                            SUMMARY:


Telecommunications requires two things:

1)      SWITCHING: The connection of user to user.

2)      TRANSMISSION: Sending the information (voice, data, video) to its destination.

Transmission can be in ONE direction ONLY at any one time, this is called SIMPLEX,
or it can be bi-directional (both ways at the same time) this is called DUPLEX.

Examples:       Simplex is like a walkie-talkie.
                Duplex is like a telephone.

Voice, computer programs, audio, video, and everything else can all be transmitted and received
as data.

Sending data from one user to another involves some sort of connection. Either a wire, an optical
fibre, or a radio circuit.
                                            3: Transmission
Definition: Transmission means sending information from one location to another.

3.1     Early History


                            transmission line




There are three things to worry about in the transmission of electrical signals:
Current (I), Voltage (V), and Resistance (Ω) which last, is given the Greek symbol omega.

The problem is, that when an electrical current flows along a wire (circuit) it interacts with the
resistance, and part of it is converted to heat, and lost.
                                        2
The LOSS is given by the equation I R so you can see, if you can cut the current down by half,
the loss is reduced by four times.

An example:

If line current is 1 amp, and line resistance is 100 ohms, loss = 1 * 1 * 100 = 100 watts.

If line current is 0.5 amp, and with the same 100 ohms, loss = 0.5 * 0.5 * 100 = 25 watts.

To reduce loss we can reduce either the resistance, or the current. It's better to reduce the
current, since the loss increases as the square of the current.

The telecomm engineers copied the power engineers to do this, and installed step-up and step-
down transformers – called 'loading coils' – in the lines.

                                transmission line




               loading coils

Bandwidth

Bandwidth is a bit like a water pipe.




Which pipe lets the most water through?
The largest one, of course.
An Internet connection is like a water pipe. If one person uses it, it's fast, provides lots of data at a
good speed. But if many people use it, the data slows down. Things take longer.

The amount of data that can pass through a transmission circuit at any one time is called the
BANDWIDTH of the connection. The highest bandwidth is provided by a Fibre-Optic circuit.

Examples of Bandwidth:

Voice telephone circuit (original copper cable, analogue) 3.3 K Bits/second

Modem (basic Internet connection)                                     56 K Bits/second

DSL (Digital Service Line)                                            256 K Bits/second

Early on, it became inconvenient to have one telephone line for every
subscriber (user). Telephones became very popular very quickly, so
some method had to be found for combining many telephone calls on
to one line.


FDM: Frequency Division Multiplexing

Can many calls be sent on one line without them all getting mixed together? You can find the
answer by thinking about some common things we use today.
How about cable TV? All the stations come on one cable, right? How come we can watch them
individually instead of all at once?
* Because each one occupies ONE CHANNEL.

             Think about a radio set. The "AM" (amplitude modulated) band starts at 550 KHz and
             finishes at 1600 KHz.
             The total bandwidth is given by f2 – f1 where f2 = 1600 and f1 = 550, so the
             bandwidth of the whole AM band is 1600 – 550 = 1050 KHz. One radio station is
             allowed to occupy 10 KHz of bandwidth.




        550 KHz                                   10 KHz                               1600 KHz
Start of AM band = 550 KHz         One station occupies 10 KHz        End of AM band = 1600 KHz

One AM radio station occupies 10 KHz of bandwidth. How many radio stations can 'fit' into the
1050 KHz of bandwidth? 1050 / 10 = 105 stations.
The "FM" (Frequency Modulated) band starts at 88 MHz and finishes at 108 MHz, so the total
bandwidth is 108 – 88 = 20 MHz. (20 x 1000 or 20,000 KHz)

Notice how the bandwidth of the FM band is about 20 times as big as the AM band.
Each station in the FM band is allowed to use 200 KHz of bandwidth. Therefore the maximum
number of stations allowed to use the FM band is:

20,000 / 200 = 100 stations.

This illustration, below, is taken from the US government site
http://www.fcc.gov/mb/audio/includes/83-oddno.htm
which is about how the frequencies are allocated to radio stations in the FM band.




Which band has the best quality sound? AM or FM? The FM band. That's because of its extra
bandwidth. More bandwidth = more quality. Why? Because MORE INFORMATION can be
transmitted per second with a wider bandwidth.

With computers, when you have a higher bandwidth, you can send and receive information more
rapidly. These days, many Internet users are paying for "Broadband" Internet service. "Broad" is
another word for "wide".

"Broadband Internet" might typically be a 256 KB/s service. What does that mean? It means that,
in theory, you could send or receive 256 Kbits (32 KBytes, because there are 8 bits in a byte) of
data, each second. And this is like having a bandwidth of 256 KHz – roughly speaking, about the
same amount of bandwidth that one radio station occupies on the FM band.

Telephone engineers used the same idea to combine lots of telephone calls into one 'band' of
signals. Once they combined them, engineers sent them all down one cable, just like using cable
TV. At the distant end, the 'band' of signals was split up again into the individual telephone calls.

This system of combining telephone calls was called FDM (Frequency Division Multiplexing). The
combined signal can be sent by radio or along coaxial cable (similar to the type used in cable TV)

Question:

If a single telephone call has a bandwidth of 3 KHz, and the transmission circuit has a bandwidth
of 12 MHz (12,000 KHz) how many telephone calls could be sent simultaneously through the
circuit?
Answer: _____________ calls.
                                      4:    THE INTERNET
Mumbai (Bombay) and the Dabba-wallahs.

Extracts from Travel-wise, "The Dabbawallahs of Mumbai"
http://www.travel-wise.com/europe/india/mumbai.html

"I am standing near Mumbai's Churchgate Station in the commercial hub of the city. It is almost
noon, and about five hundred yards away, I catch a glimpse of a man I have been waiting to see.
He wears a loose white shirt, cotton pyjamas, and, the trade mark of his profession, a white
"Nehru" cap.

His name is Naru Bhade and he is with a group of similarly clad
men who are frantically sorting out about a hundred cylindrical
metal containers ("dabbas") set out on the sidewalk. Some are
being hitched to the handles and back-carriers of bicycles, while
others are placed on wheeled wooden trolleys.

Bhade and his fellow-workers are dabbawallahs ("dabba"
translates as lunch 'box' or 'tiffin carrier'; "wallah" means a 'man').
In the next hour, he and his team, along with about 5,000 other
dabbawallahs (emerging from other suburban railway stations) will
deliver approximately 170,000 lunches from suburban households,
to schools, colleges, mills and offices spread across the entire city
and its environs.

Their customers are middle-class citizens, who for reasons of
economy, hygiene, caste and dietary restrictions-or simply
because they prefer wholesome food from their own kitchens-rely
on the dabbawallahs to deliver a home-cooked midday meal.

Amazingly enough, most of the dabbawallahs are illiterate. Yet, according to a report published
by Forbes Global Magazine in 1998, they reputedly only make one mistake for every eight million
lunches delivered-a record that would be the envy of most multinational companies, not to
mention Canada Post!

How do they do it? Each tiffin-carrier lid carries a complex coding system: colours identify each
suburb, and individual sectors of the downtown core. Dashes, crosses and dots pinpoint the
street, the building and even the floor to which the dabba will be delivered, and eventually
returned to its source.

The entire system depends on teamwork and meticulous timing. Depending upon the distance to
be covered, dabbas are collected from customers' homes between 7 and 8 o'clock in the
morning, and taken to the nearest suburban railway station. At various intermediary suburban
stations, the tiffin containers, are hauled onto platforms and sorted out for area-wise distribution,
so that a single dabba could change hands three to four times in the course of its daily journey. At
Mumbai's downtown terminus stations, the last link in the chain-a final relay of dabawallahs-fan
out to specific locations. After lunch hour is over, the whole process goes into reverse, and the
dabbas are returned to suburban households, by 6 in the evening."

                                              *******

Mumbai's dabbawallah system works very much like the Internet. The wallahs collect lunches
from a large number of locations. Each lunch carries marks that identify WHERE IT CAME FROM
and WHERE IT'S GOING.
Sun Microsystems has a short video on the dabbawallahs. You can find it here:

http://www.sun.com/executives/digitaljourney/stories/26human/index.html

When you send any information on the Internet, it works very much like the dabbawallah system!
Except that first, it has to divide your 'meal' into smaller portions.

Let's think about posting a 'normal' letter. (One written on paper and put inside an envelope)
On the front of the envelope you should put the DESTINATION address. That way, the mail
system will know where to deliver the letter.

On the back of the envelope, it is a good idea to write the SENDER's address. Why? Well,
suppose that the person who you want to receive this letter, has moved away, to a different
address? If that happened, the mail delivery person would not be able to deliver the letter.
Instead, the letter should be returned to the person who sent it. If the person who sent the letter
wrote their address on the back, then in the case where the letter can't be delivered, it can be
returned to the person who sent it. In that way, the person who sent the letter knows when it can't
be delivered.




The INTERNET works in a similar way.



                                         Your email                 TO address
              FROM address


So as to make it easier to store and send emails, early on it was decided that all files (and an
email is just a file of data, just like a music file or a video file or a program file) should be 'cut up'
into individual PACKETS. So your email, above, is cut up and might look like this:


                  TO                TO                 TO                TO                  TO
       FROM              FROM              FROM              FROM                 FROM




There's still one problem with the system as drawn above. What if the packets arrive 'out of
order'?
Your data would be 'scrambled' and unusable!
To solve this problem, each packet also contains its own sequence number, like 'This is packet
number 9' or 'This is packet 27'.
When the packets arrive at their destination, they are automatically put together in the right order.

The original reason for the Internet was to provide a method of communication that would still
work in the event of a nuclear war or other catastrophe destroying most of the communications
circuits in the USA. Imagine a case in which the major cities and towns had been destroyed. No
more mail (postal) deliveries; hardly any telephone service. The few circuits that remained
working would have to try to carry as much information as possible.
1962    Hosts: None

RAND. Paul Baran, of the RAND Corporation (a government agency), was commissioned by the
U.S. Air Force to do a study on how it could maintain its command and control over its missiles
and bombers, after a nuclear attack. This was to be a military research network that could survive
a nuclear strike, decentralized so that if any locations (cities) in the U.S. were attacked, the
military could still have control of nuclear arms for a counter-attack.

Baran's finished document described several ways to accomplish this. His final proposal was a
packet switched network.

"Packet switching is the breaking down of data into datagrams or packets that are labeled to
indicate the origin and the destination of the information and the forwarding of these packets from
one computer to another computer until the information arrives at its final destination computer.
This was crucial to the realization of a computer network. If packets are lost at any given point,
the message can be resent by the originator."

1968 ARPANET - Hosts: 4
ARPA awarded the ARPANET contract to BBN. BBN had selected a Honeywell minicomputer as
the base on which they would build the switch. The physical network was constructed in 1969,
linking four nodes: University of California at Los Angeles, SRI (in Stanford), University of
California at Santa Barbara, and University of Utah. The network was wired together via 50 Kbps
circuits.

1972 ARPANET - Hosts: 23
The first e-mail program was created by Ray Tomlinson of BBN.

1974
First Use of term "Internet" by Vint Cerf and Bob Kahn in paper on Transmission Control
Protocol.

1976 ARPANET - Hosts: 111

1981 ARPANET - Hosts: 213

1983 ARPANET - Hosts: 562
The University of Wisconsin created Domain Name System (DNS). This made it much easier for
people to access other servers, because they no longer had to remember numbers.

1984 ARPANET - Hosts: 1024

1985 ARPANET - Hosts: 1961

1986 ARPANET- Hosts: 2308

1987 ARPANET - Hosts: 28,174

1988 ARPANET - Hosts: 56,000

1990 Hosts: 313,000
Tim Berners-Lee and CERN in Geneva implements a hypertext system to provide efficient
information access to the members of the international high-energy physics community.

1991 - Hosts: 617,000
1992 - Hosts: 1,136,000
Internet Society is chartered.
World-Wide Web released by CERN.
1993 - Hosts: 2,056,000
Marc Andreessen and NCSA and the University of Illinois develops a graphical user
interface to the WWW, called "Mosaic for X". – The FIRST BROWSER.
Pizza Hut offers pizza ordering on its Web page.
First Virtual, the first cyberbank, opens.

1994 - Hosts: 3,864,000

1995 - Hosts: 6,642,000

1996 - DATE Hosts: over 15,000,000, and growing rapidly




CLASS PROJECT

Build an Excel worksheet, showing the GROWTH of the INTERNET from its start, in 1962.

Try researching in GOOGLE to find the most recent total for the number of hosts.

Make a chart showing the growth of the Internet.

Use the chart to predict, if you can, how many hosts will the Internet have in 2010?