IT280-Chapter 3
Inverse multiplexing means
combining several low speed circuits to enable them to be transmitted across one high speed circuit
Transmission speeds:
differ widely among media
The ability to transmit in both directions, but only in one direction at a time is an example of _______________ transmission.
half-duplex
To get more "bandwidth" in a digital transmission, you must:
increase the range of frequencies available for a transmission
__________ is a line-of-sight type of wireless media.
microwave
Which statement is false about modems?
modems must always be internal to the computer
A(n) ___________ divides one high-speed communication circuit into several lower speed circuits for the primary reason of saving communication line costs.
multiplexer
Frequency division multiplexing:
operates by dividing the signal into different frequencies
When converting analog voice data to digital signals, Pulse Code Modulation samples the incoming voice signal _______ times per second.
8,000
A codec converts an incoming digital signal to an analog signal for transmission over an analog network.
False
A physical circuit refers to the transmission characteristics of the connection.
False
ASCII is the coding scheme developed by IBM for its mainframe computers.
False
ASCII is the least popular code for data communications.
False
Digital transmission produces more errors than analog transmission.
False
Newer telephone circuits, built during the last decade, offer higher quality because they were built using analog transmission.
False
Non-return-to-zero is a type of unipolar signaling
False
Propagation delay is negligible with satellite transmission
False
Radio, infrared, microwave and satellite are all examples of guided media.
False
Serial mode transmission is much faster than parallel mode transmission.
False
The amount of time it takes to switch between sending and receiving in half-duplex transmission is called the propagation delay.
False
Wavelength division multiplexing can only used with copper cables.
False
______________ refers to the time it takes for a signal to travel from sender to recipient (highly exaggerated with satellite transmission).
Propagation delay
Another term for the weakening of a signal over distance is:
attenuation
The _____________ of a circuit determines a circuit's capacity.
bandwidth
The medium is the physical matter or substance that carries the voice or data transmission
True
The physical layer is the only layer where two communicating nodes are directly connected
True
The predominant method of transferring information internally in a computer is via parallel mode.
True
Time division multiplexing is more efficient that frequency division multiplexing because the guardbands used in the frequency division multiplexing or not needed.
True
The height of a sound wave is called its:
amplitude
Which of the following statements is true?
bandwidth is constant across any wire, therefore distance is not relevant to its capacity
Which type of digital signaling would experience fewer errors because it has more distinct signals?
bipolar
Which of the following would be considered a type of wireless media?
microwave
____________ refers to changing the shape of the sound wave in different ways to represent a 1 or a 0.
modulation
The acronym, Modem, stands for _________________.
modulator/demodulator
The direction in which the sound wave begins is known as:
phase
Which of the following is a characteristic of sound waves that can be modulated to convert digital data into analog signals?
phase
In which type of modulation is a 1 distinguished from a 0 by shifting the direction in which the wave begins?
phase modulation
_________ is the basic layout of the circuit.
circuit configuration
Equipment used to transform analog voice signals to digital signals and digital signals to analog signals.
codec
Data is physically transmitted from one computer or terminal to another in the ________ layer.
physical
Which is not true about point-to-point circuits?
point-to-point circuits reduce the amount of cable required and use the circuit more efficiently than multipoint circuits.
Which of the following is not an important factor to consider when selecting media to be used in a network?
prestige value of the type of media
____________ is a modulation technique that combines two different amplitude combinations with eight different phase combinations modulation to send four bits per wave, or symbol.
quadrature amplitude modulation
_____________ refers to the difference between the original analog data and the approximation of that data using the techniques for translating from analog data to digital signals.
quantizing error
When all bits of a character are transferred one after another, the bits are transferred in ___________ mode.
serial
A(n) __________ circuit is another name for a multipoint configuration.
shared
Time (non-statistical) division multiplexing differs from frequency division multiplexing because it:
splits the communication circuit vertically (with time slots) instead of
When sending four bits at a time using frequency modulation, the number of different frequency levels that would be needed would be _______.
16
Using TCM that sends 6 bits per each signal and a voice grade line with a bandwidth of 3000 Hz (assume: no noise on the line), the data capacity would be ___________ bits per second
18,000
How many bits are required to sample an incoming signal 4000 times per second using 64 different amplitude levels?
6
If the highest frequency of a circuit is 10KHZ and the lowest frequency is 900 Hz, the bandwidth available for this circuit is :
9100 Hz
The type of multiplexer that divides the circuit horizontally into different light frequencies that are transmitted simultaneously across many channels is a:
wave division multiplexer
Baud rate is the number of bits transmitted per second.
False
Coaxial cable costs less and offers less shielding to electrical interference than twisted pair cable.
False
Digital transmission occurs when the signal sent over the transmission media constantly varies among an infinite number of states.
False
Fiber optic cable can only be used on LANs.
False
Fiber optic cable carries signals in traditional electrical form
False
Frequency division multiplexing divides the circuit into a set of different time slots.
False
Frequency modulation refers to the changing of the height of the sound wave.
False
Guided media refers to the type of media in which the message is broadcast through the air
False
In a multipoint circuit configuration, each computer can use the circuit at the same time.
False
In a multipoint circuit configuration, each computer has a dedicated circuit between itself and each of the other computers in the network
False
In simplex transmission, the data flows in both directions at the same time
False
Infrared transmission uses high-frequency light waves to carry data through the air on a direct line-of-sight path between two points
False
Manchester encoding is a special type of bipolar signaling in which the signal is changed from high to low or from low to high in the middle of the signal.
False
Multimode fiber is capable of longer transmission distances than single mode fiber.
False
Multiplexing increases the cost of provisioning network circuits.
False
With modem communications, the receiving modem converts the incoming digital signal from the telephone line into an analog signal that can be understood by the computer.
False
With non return to zero signaling, the voltage alternates between zero and a positive or negative voltage.
False
Amplitude, frequency and phase are all characteristics of a sound wave.
True
An intercom is an example of half-duplex transmission.
True
Bandwidth is the difference between the highest and lowest frequencies in a band.
True
Coding schemes are groups of bits that translate into the "alphabet" of any given system
True
Computers produce digital data whose values are binary: 0 or 1.
True
Data compression can increase the throughput of a communication link.
True
Data rate refers to how often the sender can send data and is measured in bits per second
True
Demodulation is the conversation of an analog signal into a digital signal.
True
Ethernet, a common LAN technology, uses Manchester encoding..
True
Frequency is the number of cycles per second and is expressed in Hertz.
True
In full-duplex transmission, two stations can send and receive simultaneously
True
The "local loop" refers to the wires that run from the customer premises to the telephone switch of the telephone company.
True
____________ refers to the transmission characteristics of the circuit.
logical circuit
If each sample uses 16 bits and the number of samples taken each second is 8000; then the transmission speed on the circuit is?
128 Kbps
Digital Subscriber Line:
-is a fairly recent approach to provide higher data transmission rates across traditional voice circuits in the local loop -combines analog transmission and frequency division multiplexing -involves the use of a customer premises equipment (CPE) -uses a combination of amplitude and phase modulation
Microwave transmission
-is a type of high frequency radio communication -requires a clear line-of-sight path -is typically used for long distance data transmission -does not require the laying of any cable
A coding scheme that uses 10 bits to represent each character is capable of representing _________ different characters.
1024
The typical range of human hearing is:
20 to 14,000 Hz
____________ is one of the most commonly used coding schemes used in data transmission.
ASCII
With respect to converting digital data into analog signals, AM stands for:
Amplitude Modulation
___________ is not a type of digital signaling technique.
Data rate signaling
________________ separate channels to reduce interference between channels in frequency division multiplexing.
Guardbands
Which of the following is not a key advantage of digital transmission?
It permits only low transmission rates.
The earliest type of fiber optic systems were:
Multimode
With which type of digital signaling does the signal always return to zero volts after each bit?
Return-to-zero signaling
Which of the following statements is correct?
Serial transmission is slower than parallel transmission.
"Handshaking" refers the testing of the circuit to determine the optimum combination of symbol rate and modulation technique that will produce the highest data transmission rates.
True
Microwave transmissions require a line of sight between any two points.
True
Of all the media available, fiber optic provides the highest transmission speeds.
True
One form of interference with satellite transmission is called raindrop attenuation in which the transmissions are absorbed by heavy rain.
True
One way to reduce quantizing errors is to increase the sampling rate of the analog signal.
True
Radio data transmission requires that each device has a radio receiver/transmitter and uses a specific frequency.
True
Statistical time division multiplexing does not require the capacity of the circuit to be equal to the sum of the combined circuits.
True
______ is a modem standard that uses Lempel-Ziv encoding to compress data.
V.44
____________ is used by IM and other applications that provide voice services over lower-speed digital circuits.
adaptive differential pulse code modulation
Two fundamentally different types of data are:
digital and analog
The representation of the character A by the group of 8 bits, 10000001, is an example of:
digital coding
In general, networks designed to transmit primarily computer data are likely to be ________, while networks designed to transmit voice data are likely to be ________.
digital, analog
___________ refers to the spreading of the signal that different parts of the signal arrive at different times at the destination.
dispersion
Which of the following media can best withstand harsh environmental conditions?
fiber optic cable
Which of the following media has the lowest error rates and the highest transmission speeds?
fiber optic cable
Having a conversation with someone using a cellular phone is an example of _________ transmission.
full-duplex
The two basic types of media are:
guided and wireless (radiated)
Which of the following media is the least secure?
infrared
____________ transmission is prone to interference from smoke, heavy rain and fog and requires line-of-sight.
infrared
__________ is a unit of signaling speed that indicates how often the signal changes on a communication circuit.
symbol rate
_____________ is not a form of modulation used to transform digital data into analog signals.
synchronous time division
The type of media usually installed on homes and businesses by the telephone company is called ____________.
twisted pair