Physical Layer Flashcards
What is the physical layer?
The lowest level of the Internet-model that consists of actual hardware
What are NICs
Network Interface Cards are the hardware components that connect the device to the network.
- With wired networks, the connection is the socket where the network cable is plugged into.
- With wireless networks, a NIC is connected to an antenna to send and receive radio signals.
Give some examples of cables that use electric signals, and the main material
Unshielded Twisted Pair(UTP)
-Pairs of twisted copper cables. Each cable is insulated with plastic, and then each pair as well. The most common type of LAN cable, with categories. The higher the number, the better the quality
Shielded Twisted Pair (STP)
-Same as UTP but with metal shielding for better protection against magnetic interference. Best for high speed Ethernet or in environments with high electromagnetic interference.
Coaxial cables
-Inner wire, surrounded by plastic insulation and a wire mesh.
BNs use what type of cables commonly, and why?
Backbone Networks use optical fibres, because they are faster than copper cables. This is more useful with high speed connections between switches
What is a signal?
Energy travelling through a medium.
What is the difference between digital and analog waves?
Digital means that we have discrete states whilst analog means that we have waves that are continuous
Digital Signals
They are a sequence of 0’s and 1’s sent through a wire. The 0s and 1s are sent in the form of voltages.
Unipolar Encoding
Using one polarity. With 1s representing 0V and 0s representing usually 3-5V. There is a fixed time window for each bit that is being transmitted (ex. 1bit/ms), which the receiver times in order to decode the message
What are the disadvantages of unipolar encoding?
It can be difficult to distinguish between a 0V and 1V when there is noise in the signal.
Bipolar encoding
Using both positive and negative voltage to achieve a bigger difference in signal
Non-Return to Zero
The simplest form of encoding. Where 0 is positive voltage, and 1 is negative voltage. It also has a timer, in order to figure out the transmission length of each bit, but the receiver and senders’ clocks have to be perfectly synchronized otherwise not all the bits will go through
Manchester Encoding
It embeds a synchronisation signal into the data signal, which means that the receiver is constantly re-sycnchronising itself. This is self-clocking.
Explain how Manchester encoding works?
The data is transmitted in the middle of the time window for each bit. 1 is transmitted as a transition from negative to positive voltave and a 0 for vice-versa.
Explain amplitude, frequency, phase and wavelength
Amplitude is the height of a wave. Frequency determines how many oscillations per second that the wave goes through. Wavelength is the distance a wave travels during one full oscillation. Phase the direction which a wave is going
How do we transmit data using analog waves? (with respect to the three parameters)
We modify the frequency depending on whether we want to send a 0 or a 1. A higher frequency for 1 and lower for 0. This is Frequency modulation (FM)
Modify the amplitude to send a 0 or 1. A high amplitude to represent 1, and lower to represent 0. This is amplitude modulation (AM)
Modify the phase, with the wave staring in a downwards direction as 1, and starting in an upwards direction as 0. This is phase modulation (PM).
