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School/Analyse/Periode 1/Layers/1. Physical Layer.md

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+# 1. Physical Layer
+This layer is responsible for the actual physical transfer of data between devices via cables or other mediums using switches, routers, etc..
+
+This layer also converts the data into a bit-stream of 1's and 0's. 
+
+The signal convention must be the same on both devices. (Meaning of a 0 and a 1)
+
+## In depth
+Information on computers is stored in a digital format. To transmit this information we have to convert the information to signals.
+
+Physical layer is responsible for this conversion. The Physical layer deals with the actual physical transmission of electrical signals.
+
+You could say the physical layer is a bridge between real life and software.
+
+## Waves
+Waves, like you would see on a lake, or in electrical cables are made when a physical quantity changes in the form of a moving ridge.
+
+Waves by them self store no real information.
+
+## Signal
+A signal is a wave (carrier) that holds information. (wave + data = signal)
+
+The carrier is a type of wave we add our information to. In most cases a sine wave is used as a carrier wave,
+
+![[encoder.png]]
+
+A encoder converts analog or digital information in signals that can be transmitted across different [[Comminucation Mediums]]
+
+The process of adding data to a carrier wave is called Modulation
+
+## Modulation
+Adding data to carrier waves is called modulation.
+
+This can be done in 3 different ways.
+
+### Amplitude
+![[modulation-amplitude.png]]
+
+Amplitude or the strength (height) of a wave changes over time.
+
+### Frequency
+![[modulation-frequency.png]]
+
+Frequency is the amount of waves that pass a fixed point in a given amount of time.
+
+### Phase
+![[modulation-phase.png]]
+
+Phase specifies the location or timing of a point within a wave cycle of a repetitive waveform.
+
+![[modulation-phase-2.png]]
+
+## Analog
+**Analog Signals** can have a infinite number of possible values in a range.
+
+For example: 0.0 <-> 1.0
+- 0.1436367436473......
+- 0.54454764654765......
+
+**Analog data** is continuous and have continuous values. 
+Values in analog data are always changing.
+
+A good analogy for analog data is like a physical (analogue) clock with hands.
+The hands on a clock like that are always moving (continuous) and do not have a specific value.
+
+## Digital
+Digital data is information represented as a string of discrete symbols each of which can take on one of only a finite number of values from some alphabet, such as letters or digits.
+
+For example:
+- a
+- b
+- 1
+- 0
+
+These values are specific and are not changing.
+
+## Transmitting Impairments
+
+Signals most often have to deal with problems during transmission. Problems like this are called transmission impairments.
+
+Important transmission impairments are:
+
+### Attenuation
+
+Attenuation is the strength or amplitude of a signal is decreasing over time and distance. 
+
+A good analogy for this would be the loss of volume you would hear from a speaker the further you are away from it.
+
+![[attenuation.png]]
+
+This makes is more difficult to correctly capture the signal on the receiving end.
+
+We can solve this issue by dividing the communication line up in smaller segments and amplify the signal between segments.
+
+### Distortion
+
+![[distortion.png]]
+
+Distortion is the change that occurs in a signal that affects how the signal looks.
+
+For example talking to someone while behind a thick glass pane changes how you sound on the other side.
+
+We can solve this by using a lower bit rate. Bit rate is kinda like the information per second. This way the signal is less susceptible to distortion.
+
+
+### Noise
+
+![[noise-signal.png]]
+
+Noise is when data is added to a signal and therefore changing the data itself.
+
+Analogy for this when you are listening to someone talk and somebody else is talking at the same time trough your conversation.
+
+We can solve this by using a stronger signal (bit like talking louder).
+This will reduce the impact noise has on the signal.
+
+This is also called signal to noise ratio (SNR)
+
+## Transmission Media
+These signals are send through a transmission medium.  A transmission medium is a physical object that can carry the information from source to destination.
+
+Transmission mediums are often space (air), metallic cable or fiber optic cables.
+
+Transmission media are divided in 2 groups.
+
+### Guided media
+Guided media like cables provide a conduit from one device to another.
+I like to think of it as you can steer the signal by moving the cable for example.
+
+Coaxial cable, twisted pair cable and fiber optic cables.
+
+![[type-cables.png]]
+
+### Unguided media
+Unguided media transport electromagnetic waves without using a physical conductor.
+
+This is called wireless transmission. (Technically using the air around you as a conductor)
+
+Signals are broadcast tough space and thus available for everyone to pick up.