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48 Cards in this Set

  • Front
  • Back
a series of electrical, radio, or light
Physical Layer
specifies the type of connection, and
the signals that pass through it
Physical Layer
are made of square waves.
Digital transmissions
Radio, Broadcast
Analog Data; Analog Transmission
Digital Data; Analog Transmission
PCM & Video
standards using
Analog Data; Digital Transmission
LAN Cable
Digital Data; Digital Transmission
commonly used for telephones and local
area networks
Twisted Pair
reduced electromagnetic interference
Twisted Pair
More expensive than twisted pair and shielded
LED (Light Emitting Dode)
Fiber Optic Cable
Sometimes called “dedicated circuits”
Point-to-Point Configuration
Many computer connected on the same circuit
Sometimes called “shared circuit”
Multipoint Configuration
Used when computers generate enough data to fill the capacity of the circuit
Point-to-Point Configuration
Used when each computer does not need to continuously use the entire capacity of the circuit
Multipoint Configuration
data flows move in one direction only, (radio or cable television broadcasts)
data flows both ways, but only one direction at a time (e.g., CB radio, it requires control info)
data flows in both directions at the same time
Breaking up a higher speed circuit into several slower (logical) circuits
Makes a number of smaller channels from a larger frequency band by dividing the circuit “horizontally”
(USed by most CATV)
Frequency Division Multiplexing
Dividing the circuit “vertically”
Time Division Multiplexing
Designed to make use of the idle time slots
Statistical TDM (STDM)
Shares the load by sending data over two or more lines
Inverse Multiplexing (IMUX)
Earliest fiber-optic systems
Signal spreads out over short distances (up to ~500m)
Multimode (Optical Fiber)
Reduces the spreading problem by changing the refractive properties of the fiber to refocus the signal
Can be used over distances of up to about 1000 meters
Graded index multimode (Optical Fiber)
Transmits a single direct beam through the cable
Signal can be sent over many miles without spreading
Expensive (requires lasers; difficult to manufacture
Single mode (Optical Fiber)
Sends bit by bit over a single wire
Can be used over longer distances since bits stay in the order they were sent
Serial Mode
Uses several wires, each wire sending one bit at the same time as the others
Used for short distances (up to 6 meters) since bits sent in parallel mode tend to spread out over long distances
Parallel mode
Use voltages either vary between 0 and a positive value or between 0 and some negative value
Unipolar signaling
Use both positive and negative voltages
Experiences fewer errors than unipolar signaling
Signals are more distinct (more difficult for interference to change polarity of a current)
Bipolar signaling
Signal returns to 0 voltage level after sending a bit
Return to zero (RZ)
Signals maintains its voltage at the end of a bit
Non return to zero (NRZ)
Used by Ethernet, most popular LAN technology
Defines a bit value by a mid-bit transition
A high to low voltage transition is a 0 and a low to high mid-bit transition defines a 1
Manchester Encoding
Height (loudness) of the wave
Measured in decibels (dB)
Number of waves that pass in a second
Measured in Hertz (cycles/second)
Wavelength, the length of the wave from crest to crest, is related to frequency
Refers to the point in each wave cycle at which the wave begins (measured in degrees)
Speed =
Frequency x wavelength
Μodification of a carrier wave’s fundamental characteristics in order to encode information
Basic sound wave transmitted through the circuit (provides a base which we can deviate)
Carrier wave
Changing the height of the wave to encode data
Amplitude Modulation (AM)
Changing the frequency of carrier wave to encode data
Frequency Modulation (FM)
Changing the phase of the carrier wave to encode data
Phase Modulation (PM)
Use each modification of the carrier wave to encode information
Combine Amplitude and Phase Modulation
QAM - Quadrature Amplitude Modulation
a unit of information
a unit of signaling speed
Number of bits transmitted per second
bit rate
number of symbols transmitted per second
baud rate