3.1 KiB
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,
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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
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Amplitude or the strength (height) of a wave changes over time.
Frequency
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Frequency is the amount of waves that pass a fixed point in a given amount of time.
Phase
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Phase specifies the location or timing of a point within a wave cycle of a repetitive waveform.
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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.
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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