Fichas
The Physical Layer (2)
Fichas del conjunto (20)
- 1Give ecamples of guided mediaGuided media (provide physical path) and unguided media (air, vacuum or water)
Guided: Twisted pair, coaxial cable, power lines, fiber optics. - 2Twisted what are 2 types?telephone lines, LANs, 4 pairs, twisting reduces noise as magnetic fields induce currents in opposite directions. 2 types: unshielded twisted pair (UTP), Shielded Twisted Pair (STP) – additional shielding
- 3CoaxialEthernet Lans, cable tv and MANs, good shielding reduces noise, more bandwidth for longer distances and higher rates than twisted
- 4Power linesnetwork that uses household electrical wieing, convenient but not great
- 5what are the 2 types? fiber optics: long distance ISP links, fiber-to-the-home. Common high rates and long distances enourmous bandwidth and tiny singal loss. Light carried in a very long thing strand of glass. 2 types: multi-mode – light bonce winder core. Used with LEDs for cheaper shorter. Single-mode: core so narrow so light can’t bounce around. Used with lasers.
- 6radioUnguided: radio, microwave, infrared
Radio signals penetrate buildings well and propagate for long disatnces - 7microwavemuch bandwidth and widely used indoors (WiFi) and outdoors between amsts of 4G, 5G, networks, between satellites) attenuated/reflected by everyday objects. Strength varies with mobility due multipath fading…
- 8Infared Transmissionshort-range communication, doesn’t pass through solid objects
- 9Signal is affected by? 3- Attenuation: loss of signal strength over distance
- Distortion: alteration of signal shapre or form (indced by attenutaiton, noise or delay)
- Noise (internal or external): random or unwanted signal that mixes up with the original signal - 10parallel transmisisonhigh bit rate – transmits group of bits simultaneously. Expensive over long distance as need thicker cable. Synchronisation problem over long distance (bit skew)
- 11serial transmissionslower than parallel, one bit after another. More reliable and cheaper for long distance. Incurs additional complexity for sending and receiving devices
- 12multiplexing what are the 3 major techniques?: allows carrying of multiple signals of a single medium (share a channel among users) – more efficient use of transmission medium. 3 major techniques:
- Frequency-division multiplexing(FDM)
- Time-division multiplexing(TDM)
- Code Division Multiple Access(CDMA) - 13FDMshares channel by placing users on different frequencies. Useful bandwidth of medium exceeds required bandwidth of a given signal. Filters used at receiver to separate channels. ** go over
- 14TDM: shares a channel over time. Achievable bit rate of the medium exceeds required data rate of a digital signal.
- 15CDMAshares channel by giving specific code to users. 3G. (like a tree)
- 16line codesdigital data to digital signal. Represents bit stream.
* on exam especially manchester encoding - 17NRZNRZ(Non-Return-to-Zero) +1V=1 -1V=0
long stream of bits introduces a synchronization problem. CLockes of the sender and receiver never run exactly at same speed. To deal use separate clock wiere. (only short distances). Embed clock signal into bit stream. - 18RZ/Manchester NRZIRZ/Manchester – clock extraction circuit at receiver uses transitions to regenerate clock signal. NRZI – use bit stream to synchronise receiver clock occasionally. Occasional presence of signal tranisaitons.
- 19GE ThomasG.E. Thomas: High-to-low transition (Negative edge) in middle of bit is 1
Low to high transition (positive edge) in middle of bit is 0
If goes down = 1 if goes up = 0 - 20NRZINRZI means invert of 1. Presence or absence of change indicates 0/1
Change at bit boundary means 1. No change = 0
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- Uni (Software Systems) Uni Second Level Fichas sobre The Physical Layer (2), creado por HRYN red el 18/11/2024.
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- HRYN red
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