The Numericos Islands an Exercise in Communications

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The Numericos Islands an Exercise in
Communications
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• Lesson Objectives
• Convert numbers between bases 10, 2 16
• State the purpose of each layer of the ISO
• Basic Reference Model for OSI
• State the meanings of a number of
• data comms networking acronyms
• Work in small groups to plan a simple data
• communications system

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Discovered each others existence
85 years ago
or 55 years ago
or 1010101 years ago
or 125 years ago
depending which island youre on
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You see,
The Decimalians use base 10
the Hexians use base 16
the Binarians use base 2
and the Octavians use base 8
number systems
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So,
The Decimalians say 85 years ago
The Hexians say it was 55 years ago
The Binarians say 1010101 years ago
And the Octavians say 125 years ago
and theyre all telling the truth!
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Back in the Old Days,
Everyone feared the Binarians
Because they had an army of 10000
The Decimalians found out it was 16
And the Octavians that it was 20
And the Hexians that it was only 10!
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Why should we be interested in this?
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Because
Networking is awash with numbers
In binary, e.g. a flag in HDLC is 01111110
In decimal, e.g. a subnet mask 255.255.255.0
In octal, a files permissions 777
In hexadecimal, a MAC address 3C-01-D4-2F-04-31
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Some more Numericos problems
The Hexian population was BEEF
9 Years earlier the population was DEAF
Then it was actually DEAD
Theyd had BAD tourists from the other islands
The Decimalians asked the others to send teams of
11 football players!
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Some more Numericos problems
The Octavians sent nine
The Hexians sent seventeen
The Binarians sent three
Plus a sub.
However, the Islanders managed to trade with each
other reasonably well, after
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The Bosses had a Meeting
They would set up a business mail service to help
speed up trading between the islands.
Every island would have three boats, each one
delivering mail to one of the other islands.
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The mail boat routes
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Things were going well
Then the Duodecimalians decided theyd like to
join in
The others all agreed it was a good ideathen
President Evan Zabuv from Binarios said the
Alphabeticos islands wanted to join, too
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OK, Lets get their mail boats ready
Alec Tronnicks from Decimalia said theyd need
930 altogether!
Four existing islands DuoDec. 26 Alpha.
31 So each island needed 30 boats 30 x 31 930
far too many! So, the mail expansion was halted.
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They all went home fed up
Alec pondered the question for weeks, and months,
thenEureka! One boat could do it
Just have one boat visiting all the islands and
it could pick up and drop off and all the islands
could join in!
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So they all chipped in for the Island Queen
One day, Alec had a visit from Cilla ScopeShe
told him things could move much faster than the
speed of boats Do it with wires, Alec
She showed him how computers could communicate,
and Alec was impressed.
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Cilla went home and Alec thought about wires
Alec thought it would be a good idea to set up a
system of wires between the four main islands. He
sent letters to his three friends
Then he thought about the problems of sending
messages between them all - you have copies of
his notes
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Alec broke the communication problem down bit by
bit
Starting with the basic problems of voltages and
wires and connections, Alec worked methodically
through all the problems he needed to overcome in
order to send a complete message between two
people on two islands
He used seven key terms in his descriptions of
the problems
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These are Alecs Seven Key Terms
Application Presentation Session Transport Network
Data Link Physical
These are the same terms used by the
International Standards Organisation for its
Basic Reference Model For Open Systems
InterconnectionThe OSI model !