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Lecture notes on Digital Communication
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Notes of all the lectures of G. Mills on Digital Communication.
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DIGITAL COMMUNICATIONLECTURE 1: Historical background to Digital
Communication
The simplest form of digital system is 0 and 1 (OFF/ON)
The boundary between digital and analogue is blurred: for example, digital audio recordings use
analogue systems.
Spoken language is digital and analogue:
The way you use words to make sentences and make words is digital; it is the one or the other. The
way you talk is analogue; pitch and volume.
There are different types of digital communication:
- Machine with machine
USB, Bluetooth
- Human with human (through a computer)
- Human with machine (conversation)
Siri, customer services hotline
- Human with interface
pilot control in an airplane, DVD player menu
There were different ways of communicating with each other when there was no internet:
- Slit drums
A long wooden tube on which people would drum so they could send a message to the next
village.
Three ways of communicating:
1. Making music together
2. Encoding messages with specific patterns
= fully digital communication
3. Copying the patterns of speech
- Greek hydraulic semaphore system
Sender and receiver have the same pots with water in it. In the pots were
floating sticks with messages on them. At the same time, sender and receiver
let the water out of the pots. When the water is at the edge, the floating stops
and the receiver looks at the message on the edge. The messages were selected
from a pre-existing list.
- Optical telegraphs (semaphore)
A big tower with wooden arms that could be directed in lots of ways. It had
three linked arms which can be moved separately: 98 positions.
This was fully digital communication.
There were also control signals, such as ‘message received’ or ‘please wait’.
These types of signals are also found in speech: ‘go on’ ‘what did you mean?’
Digital is not necessary electronic.
,Sommering invented the electric telegraph. It used 35 wires to represent all the Latin letters. The
sender passes an electric current through the wire for each letter. The receiver reads what letter is
sent by seeing where the bubbles form in the tower. This could transmit messages up to 4 km.
Morse (1820) invented a way of communicating over long distances: Morse code.
In 1850 the first transatlantic cable was laid through the Atlantic Ocean. 20 years later, there were
cables all over the world. To convey messages through these cables, telegraph operating rooms
were set up. Here people would pass on the Morse messages to other operating rooms. Some people
working here could even recognize other people on their code style. They could recognize gender,
accents and individual patterns.
Abbreviations were already used in Morse code. Also, spam was active in Morse code.
LECTURE 2: The internet (past and future)
The development of the internet consists of 2 parts:
- The technological part
- The effect of the development on social issues
The Morse key became smaller and smaller. The smaller it gets, they found out it vibrates sound. Out
of this became the telephone (1880, Bell).
To communicate via telephone, there was a new convention created: the use of ‘Hello’. Before the
telephone, hello was only used as a way of attracting attention and a mild form of surprise. Since
using the telephone, hello was used as a greeting.
Telephone was originally intended to be used for ‘theatrophone’. They put the phone on
microphones in concert halls and theatres and then you could ‘stream’ all over the world. After a
while they began using it for conversations.
Strowger came with the automatic switch for telephones, so the women who would send you
through were replaced by technology. The clicking in old telephones is clicking through the different
numbers and lines. By designing this, he solved a few problems:
- Unintended human errors
- Speed of making a connection
- Direct dialing
- Lowering the costs of running a local exchange
- Deliberate human error
1950
Internet was developed by the military. The Russians launched a satellite
(Sputnik) and the US military was scared is was used as a weapon. They used
, the internet as an automatic communications network what still would work when bits of it were
destroyed. This is called decentralized; there is not one central power. This way, it can survive a
nuclear attack.
It was called the ARPAnet: Advanced Research Projects Agency
In 1973 the ARPAnet goes international
In 1971 was the first email written. Up till then, you could only send a message to someone on the
same computer. Tomlinson came with the solution: dividing the username with the computer name
with a @ (elin@computer)
The internet is a network of networks. The internet connect the ARPAnetworks.
The internet searches per place which route is the shortest. (just as with the ARPAnet).
Packet switching is when one message is split up in different pieces, which all ‘travel’ by different
routes.
Berners-Lee invented the World Wide Web -> you can click on text or images that redirect you to
other text or images. (= hypertext) It is a document that contains links to other documents. The http
(hypertext transfer protocol) is for the communication between webservers to interact with each
other. This is how a client and server communicate with each other to download text, images and
movies.
Lynx was the first browser.
Mosaic was the first browsers with images (de hele oude grijze versie van windows).
The stock price of internet went up and up until 2001, when it crashed. This was because they could
not make it work. The internet should be used for connecting people to each other. At first, it was
used to connect people to programs.
The period before the crash is called Web 1.0, the period after the crash is Web 2.0.
Web 1.0: connecting people to programs. (person to online news, shopping) Before 2001
Web 2.0: connection people to people. (Facebook, Twitter) After 2001
Software should:
- Connect people
- Emphasize online collaboration, discussion, sharing content
- Be social
99% of internet traffic is underwater with cables.
With new technologies, there comes new behavior. People don’t know yet how to behave, so these
should be new social rules. Just as there was a behavior book for when the telephone was invented,
there was also a behavior book for Google Glasses.
LECTURE 4: What exactly is a computer: Future of
computing
What is a computer? -> Commando’s come in, announcements come out.
The original computers were people.
Zero’s + one’s is the language of computers
How original numbers work;
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