Flashcards
midterm
Flashcards do conjunto (14)
- 1Bipolar (two-way) NRZ vs RZ (line coding)voltage is positive or negative, but not
zero
NRZ: big block
RZ: short bock with tail (return to zero) - 2Unipolar (one-polar) RZsignal values are 0 Volts or some positive voltage (return to zero)
- 3Unipolar (one-polar) NRZignal values are 0 Volts or some positive voltage
- 4Describe what is meant by noise?is undesirable signal that impacts the quality of a desired signal In telecommunication networks noise comes from:
– Electromagnetic interference (EMI)
– System processing - 5Differentiate between digital and analog transmission– Digital signal: e.g. turn a switch on or off depending upon whether data to send is 0 or 1 (Digital signals are more immune to noise)
– Analog signal: e.g. create a sine wave and change (modulate) its amplitude or frequency, hence the names AM and FM - 6Explain what is meant by codingEncoding is the mapping from characters to bits.
- 7Describe what is sampling, and what is Nyquist theorem, what is meant by aliasingSampling the analog signal at regular time intervals
Nyquist signal must be at least twice the rate of the maximum frequency rate of the signal.
Aliasing when the signal is misidentifying when sampled at a rate lower than twice its maximum frequency - 8Explain the quantization processthe samples into a finite number of levels.
Idea: continuous amplitude is mapped to a finite set of amplitudes
b = log2 (M)
- 9Explain why we need Pulse Code Modulation (PCM) b = log2 (M)This allows us to convert analog signal, such as in voice transmission, to be encoded into to bits.
Definition: The conversion of a quantized signal into bits is essentially what we call as “pulse code modulation” or PCM - 10Describe the different types of line codesUnipolar: (RZ), (NRZ)
Bipolar: (RZ), (NRZ) - 11Describe Manchester encodingA special type of Bipolar, Manchester encoding is used in Ethernet.
Transitions in the middle
Signal power is the same as Bipolar NRZ
Less susceptible to have errors undetected
- 12Explain the meaning of a signal and why it is needed in networksA signal is generated from data and can be transmitted through electromagnetic freq. or wavelength across physical mediums or through the air to a receiver.
A signal allows us to transmit digital or analog data. - 13Explain the meaning of a channelChannel is the physical medium which we transmit signals over.
- 14Describe different channel impairments– Delay: propagation, queuing
– Losses: attenuation: energy is absorbed (through heat) and loses intensity.
Dissipation (energy gets scatters in many directions and loses intensity.
– Noise:
White Noise: - Due to random fluctuation of electrons – Is a function of absolute temperature
Impulse noise:
– Generated by natural and man-made sources
– Consists of voltage spikes – Random arrival
Informações
- Descrição
- Telecomm 1070 FlashCards sobre midterm, criado por David Hinton em 03-03-2017.
- Criado por
- David Hinton · mar 2017
- Atualizado
- 3 mar 2017
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