Physical Layer - CH 3 (EXAM 1) Flashcards
What is the physical layer?
layer 1 in the internet model
contains physical and logical circuits to send transmission to data link layer
What are the 2 types of circuit configuration?
point to point (wired) - server – client computer
multipoint (wireless) - client computer - client computer
What is simplex data flow?
data flow in ONE direction
What is half-duplex data flow?
data flow in BOTH directions (one at a time)
What is a full-duplex?
data flows simultaneously in BOTH directions
What is multiplexing?
dividing high speed circuits into slower logical ones
saving $$$
frequency and time
What is frequency division multiplexing?
creates channels from the LARGER frequency band
guardbands separate channels to prevent interference
What is wavelength division multiplexing?
a variant of FDM in fiber optics circuits
makes use of MULTIPLE wavelengths to divide circuits into channels
What is time-division multiplexing?
circuit divided by devices taking turns
more efficient than FDM
equal turns
What is statistical time division multiplexing?
variant of TDM
reduce time slots based on network usage
may cause delays when usage does not match allocated slots
What is inverse multiplexing?
combines low-speed circuits into high-speed
What is media?
physical manner to carry vice or data transmission
What is guided media?
transmission flows along physical media
What is wireless media?
transmission flow through the air
What is a twisted pair cable?
guided media
(twisted-pair cable)wires bundled together
used for telephones and LAN
What is a coax cable?
guided media
single copper core, outer insulation, shielding, inner insulation
less prone to interference
cable tv / internet
What is a fiber optic cable?
guided media
optical core made of glass or plastic
data transmitted through LED’s
extremely fast data rates
What are fiber optics?
multimode
graded-index multimode
single-mode
What is a radio?
wireless media
wireless transmission of electrical waves through air
mobile network communication
cordless, wireless LAN
What is a microwave?
high-frequency radio communication
requires line of sight which requires antennas and towers
What is a satellite?
special form of microwave communication
long distance leads to delays
What are the factors of media selection?
network type cost transmission distance security error rates speeds
What is a digital-analog?
discrete binary values (01)
What is an analog?
transmission involves continuous waves (sin, cos)
What is a parallel transmission mode?
multiple bits transmitted simultaneously
What is a serial transmission mode?
bits transferred sequentially one at a time
What do the sender and receiver have to agree on?
set of symbols (voltages or light pulses) symbol rate (how often sent)
What is a unipolar signaling technique?
voltage is 0 or positive
represents binary bits
What is a bipolar NRZ signaling technique?
voltage is positive or negative but NOT zero
What is a bipolar RZ signaling technique?
voltage is positive or negative returning to 0 between each bit
What is a bipolar AMI signaling technique?
voltage is 0, positive, negative, returns 0 between each bit, and alternates between a negative and positive voltage
What is a manchester signaling technique?
voltage is positive or negative and bits are indicated by a mid bit transition
What system was built for analog data?
telephone
needs a modem to convert analog to digital
What are the 3 characteristics of waves?
amplitude (height of the wave)
frequency (waves/second)
phase (wave direction in degrees)
What is a carrier wave?
basic wave transmitted through a circuit
What is modulation?
modification of carrier wave’s fundamental characteristics in order to encode information
What are the 3 ways to modulate information?
amplitude modulation (AM) frequency modulation (FM) phase modulation (PM)
What is a symbol?
+1 modifications to a carrier wave used to encode data
one bit defining two different symbols
What is 2-bit amplitude modulation?
2 bits transmitted per symbol (4 levels defined as symbols)
What is the data rate?
data rate = symbol rate * (#bits/symbol)
What are codecs?
device or software converting analog signals into digital form and vice versa
What is pulse code modulation?
converts analog to digital
sampling analog signal
measuring amplitude of each sample
encoding amplitude as binary data
What is quantizing error?
difference between an original analog signal and approximated digital signal
How can you reduce quantizing error?
sampling more frequently
using more levels of amplitude in encoding
