These are the notes of all the lessons of Digital Communication, 2020/2021. In the notes there are also many examples that will help you understand the substance better.
Digital comes from the Latin digitus which means finger
Why is this important?
Numbers are counted of fingers
If something is digital, it can be counted discretely 0,1,2,3,4,5,6…
If you talk and you explain something with counting it’s digital. If you talk face to face you
can talk in different volumes so analogue. Soundwaves are analogue. If the information is
transmitted in “buckets/containers” its digital. If it can take many values, its analogue. The
choice of words is a digital system. If you are screaming or whispering, its analogue.
The opposite of digital is analogue
A number that is continuous (no discrete values /infinity of values)
- History of communications:
- Communicating via drums. (making music together, encoding messages, copying the
patterns) This is fully digital communication, but also analogue in the mimic of
speaking
- Greek hydraulic semaphore system
- Optical telegraphs (end 1700) fully digital communication and use of control signals.
These signals are also found in social media: two blue ticks in whatsapp.
- Electric telegraph (1809). 35 wires to represent all the Latin letters.
Morse code:
Samuel Morse, 1820. Dot – Dash. Truly digital (key pressed vs key released)
e.t.a.i.n are the 5 most frequent letters in English.
Same principle is used in ZIP files.
In morse al afkortingen vanaf 1870
- First commercial telegraph 1844
- Transatlantic cable 1850. Tussen Amerika en Engeland d.m.v schepen
- The Victorian “internet” (1870) via morse. Allemaal kabels door de hele wereld
waardoor ze konden communiceren via morse/telegraph.
Digital to analogue:
- The telephone (1880)
Ontstaan van nieuw woord/taal:hallo
- Telephone regels/directory:1878. Start with hello, end with that’s all. Other has to
say: ok.
- First streaming of music 1880’s
- Telephones were connected to human operators who connects you with the other
person.
The invention of automatic switching: Strowger decided to find a way of replacing human
operators with an automatic switchboard. Solve human error.
,History of internet
- 1957 Russia launched the first satellite Sputnik.
USA created special agency ARPA. Military communication network. Decentralized -
that still works if parts of it were destroyed.
ARPA-Net. 4 cities in US west-coast and Utah.
- 1970/1971 ARPA-Net grows. From west-coast to east-coast university to university.
- 1971 first e-mail
- 1972 3 connections west to east ARPA
- 1973 ARPA goes international. London and Norway
- 1978 First E-mail spam. After that 10 years of no spam.
- 1982 first smiley
3 kind of networks:
- Centralised
- Decentralised
- Distributed
Internet is a decentralised network of networks. Communicating using a shared standard.
Internet routing: Each router has a lookup table (like a directory) of the best next node to
send to for any destination. If parts of the internet are destroyed, the internet adapts,
sending it via a different route. Pachet Switching.
- 1988 first internet chat
- 1989 World Wide Web(www)
- 1993 first webcam
- 1997-2001 internet bubble and crash
Web 1.0 before crash: Connecting people to programs
Web 2.0 after crash: Connecting people to people.
- 99% of internet is underwater
Recentralized by social media platforms.
Digital or Analogue:
Digital: Letters, words, sentences. CAR vs CAT. Changes meaning entirely.
Analogue: Volume, pitch, duration: yeah vs yeahhh vs yeahhhhhhh
Digital communications:
- Machine with machine (wifi, internet router, Bluetooth)
- Human with human (whatsapp, social media)
- Human with machine (siri, human robot interaction)
- Human with interface (dvd player menu, pilot controls in an aeroplane)
Different communications:
- Face-to-face communication
- Computer-mediated communication
- Human computer interaction
- Human robot interaction
, LECTURE 2:
What is a computer?
A computer exists out of microchips.
Input where it comes in
Output where it leaves
Binary is communications between machines
Information is transmitted through very small wires. Wires can only be 0 and 1.
0=off
1=on
If you have 110001 the sum is:
1x1=1
2x0=0
4x0=0
8x0=0
16x1=16
32x1=16
=49.
Each of these “containers” is a bit. A bit can be either 0 or 1
Why binary? It’s much easier for electronic devices to use. 0=off 1=on
Binary allows logical operations.
Not And OR
A=0 X=1 A=0 B=0 X=0 A=0 B=0 X=0
A=1 X=0 A=0 B=1 X=0 A=0 B=1 X=1
A=1 B=0 X=0 A=1 B=0 X=1
A=1 B=1 X=1 A=1 B=1 X=1
Harvard architecture: Data and instructions are separated.
Von Neumann architecture (inside most PC’s): Data and instructions are stored and
processed in the same channels.
Before computers a machine only did one single task.
The computer separates properties of the physical machine (hardware) from the
specification of the steps followed by the machine (software).
Anatomy of a google search:
Step 1: Browser checks cache
Step 2: Browser checks expiry date
Step 3: the browser checks to see if it knows the server’s ID Address (similar to post
addresses)
Step 4: But what if your browser doesn’t know what the IP-Address is? (root)
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