physical layer

what is the role of the physical layer?

to move raw bits between physically connected systems using specified standards for signaling, connectors, and synchronization

what’s the difference between analog and digital data?

analog is continuous, digital has discrete values

what’s the difference between analog and digital signals?

analog have infinite levels, digital have limited/defined levels

define bandwidth in signal transmission

the difference between the highest and lowest frequencies in a signal

what are the 3 main causes of signal impairment?

attenuation, distortion, and noise

what is jitter?

variation in delay between consecutive packets

what is line coding?

converting digital data into digital signals

what is block coding?

adds redundancy for synchronization and error detection by converting m bits into n bits (n > m)

what is scrambling?

modifies line/block coding to break long sequences of zeros using rules like B8ZS and HDB3

what does PCM stand for, and what are its steps?

Pulse Code Modulation
sampling → quantization → encoding

what is the sampling theorem?

sampling rate must be at least twice the highest frequency

fs >= 2 x fmax

what is delta modulation?

only the change from the previous sample is encoded and transmitted

what is the difference between parallel and serial transmission?

parallel sends multiple bits at once; serial sends one bit at a time over a single channel

what is Amplitude Shift Keying (ASK)

varies amplitude to represent data; frequency and phase stay constant

what is Frequency Shift Keying (FSK)

varies phase to represent data; amplitude and frequency stay constant

what is Phase Shift Keying (PSK)

varies phase to represent data; amplitude and frequency stay constant

what is Quadrature Amplitude Modulation (QAM)

combines ASK and PSK using in-phase and quadrature carriers

what is Spread Spectrum and why is it used?

adds redundancy to avoid interception/jamming in wireless; used in DSSS and FHSS

what is the difference between FHSS and DSSS

in FHSS data hops across multiple frequencies; in DSSS each bit is replaced with multiple chips using a spreading code

what are the 3 types of guided media?

twisted pair. coaxial cable, fiber optic

what are the 3 types of unguided media?

radio waves, microwaves, infrared

which medium is best for long-distance, high-speed communication?

fiber optic cable

which unguided medium cannot penetrate walls?

infrared