IT300 Midterm Review

How do coaxial cables prevent RF interference?

By use of a properly grounded conductive shielding surrounding the signal wire

What is reactance?

The time-dependent elements of capacitance and inductance are called reactance, and they are present when AC signals are. Reactance in a circuit causes a phase angle difference thus reducing power efficiency if not corrected.

What deos a BER of 10^-4 mean?

There is a probability of one error for every 10,000 bits transmitted

Which OSI reference model layer provides information regarding the proper application port that received data should be sent to?

Transport Layer 4

Depolarization of a transmitted signal reduces the amount of energy transfer between the RF wave and antenna True False

True

It is useful to observe information signal in both the time and frequency domains. The time domain gives us information about the signal's amplitude over time, while the frequency domain gives us information regarding signal frequency and bandwidth. True False

True

Network availability takes into consideration both the amount of time that the network fails and is not functioning, as well as the time it takes to bring the network back into full service. True False

True

Only MMF cores can be constructed as step-index or graded-index cores True False

True

Radio Frequency (RF) signals propagate as an electromagnetic (EM) wave. Optical signals behave as both a wave and as a particle as it propagates. Although optical waves possess this "wave-particle duality", they are still considered EM waves. True False

True

Signal modulation is used to mix a baseband signal with a carrier wave for the purpose of relocating the modulated channel to the higher carrier frequency. True False

True

What is Ohm's Law?

V=IxR, V = Volts, I = Amperes, R = Ohms

Which of the following describes the relationship between current (I), voltage(V), and resistance (R)?

a. V = IR b. I = VR c. R = IV d. V = I^2R a. V = IR

A five-bit dataword can represent how many encoded symobls? a. 16 b. 32 c. 64 d. 128

b. 32, 2^5

Select the true statement regarding error control algorithms a. ARQ is solely an error detection algorithm b. the concept of codeword and dataword is only applicable to error correction c. CRC is an error detection method that requires the use of a shared polynomial between communicating nodes d. PCM is a prime example of an error detection method

c. CRC is an error detection method that requires the use of a shared polynomial between communicating nodes.

Select the correct statement regarding antenna beamwidth

c. beamwidth decreases as frequency increases

Select the correct statement(s) regarding electrical and electromagnetic (EM) information/signal waves. a. an electrical signal traveling through a guided conductive wire will create a surrounding EM wave that is proportional to the current. b. electrical and EM signals carrying information will have an associated bandwidth that can be seen in the frequency domain. c. an EM wave in the RF part of the spectrum will create a current in a receive antenna that is proportional to the RF wave. d. all are correct answers.

d. all are correct answers

Select the correct statement(s) regarding Hartley's Law. a. Hartley's Law gives us a relationship between baud rate ( symbols per second) and data rate ( bits per second) b. by increasing "M" you also increase bit rate c. by increasing baud rate, you also increase bit rate. d. all are correct statements.

d. all are correct statements.

Select the correct statement(s) regarding digital baseband modulation. a. with digital modulation, logical "1s" and "0s" are encoded to specific values of carrier wave amplitudes, frequencies or phase angles b. QAM is a modulation technique in which both carrier amplitude and phase angle changes represent logical data. c. with QAM, two carrier waves of the same frequency, but separated by π/2 radians, are used to represent logical data. d. all statements are correct

d. all statements are correct

Select the correct statement(s) regarding the Shannon-Hartley Capacity Theorem.

According to the theorem an increase in signal bandwidth or SNR resutls in an increase in bit rate capacity.

What is an electromagnetic wave? How does it relate to acoustic, RF, and optical signals?

An EM Wave is when a moving magnetic field causes an electrical current to flow through a wire. Conversely, a changing current traveling through a conductive wire will produce both an electrical field (E-Field) and a magnetic field (H-Field) in free space around the wire. Whenever the E-Field is present, so is the H-field, and thus the combination of fields is termed electromagnetism.

What is correct regarding an ideal isotropic antenna? a. An ideal isotropic antenna is a highly efficient antenna used extensively in today's communication systems b. An ideal isotropic antenna is a specialized antenna used to direct EM signal energy towards a specific direction c. An ideal isotropic antenna is a theoretical antenna that does not exist in practice, but is useful in explaining power density and unguided EM signal attenuation. d. None of the above

C. An ideal isotropic antenna is a theoretical antenna that does not exist in practice, but is useful in explaining power density and unguided EM signal attenuation.

A telephone is an example of: a. simplex communications b. half duplex communications c. full duplex communications d. complex communications

C. Full Duplex Communications

___________ noise is caused when the same frequency is used by adjacent transmitters that interfere with one another.

Cochannel Interference (CCI)

Select the correct statement(s) regarding packet switching

Connection oriented circuits must use overhead to establish communications prior to data exchanges between nodes.

Select the correct statement(s) regarding partial mesh networks. a. The number of links connecting nodes in a partial mesh network depends upon the availability and reliability requirements of the network. b. Switches play an integral role in a partial mesh network, where several paths through the network are available. c. Redundant links and switches are used to improve the availability and reliability of partial mesh networks. d. All statements are correct.

D. All statements are correct

Describe the difference between a DC (direct current) and AC (alternating current) circuit.

DC circuit is in the same direction, AC circuit is constantly switching. In a DC circuit, voltage remains constant as does the direction of the current. The voltage in AC circuits changes with time between positive and negative values, resulting in changes in the direction of current within the circuit.

Select the correct statement regarding DCE and DTE interfaces

DTE and DCE describes the interface and direction of data flow between devices; a single device may have botht ypes of interfaces.

What is true about delay skew?

Delay skew exists in UTP cables where each wire pair is twisted at different twist ratios

Select the correct statement regarding circuit switching.

During a circuit switched connection, a physical path through the network is established, but only for the duration of the call.

A unipolar signal crosses zero, while a bipolar signal always remains positive. True False

False

Optical signals are not part of the electromagnetic (EM) spectrum. Only radio frequency (RF) waves are considered part of the EM spectrum. True False

False

Orthogonal Frequency Division Multiplexing is a spread spectrum technology. True False

False

The noise floor includes thermal noise, impulse noise, intermodulation noise (IM), and cochannel interference (CCI). Link margins are only added to counter weather. True False

False

How does a DC Circuit differ from an AC Circuit?

In a DC circuit, the electrons flow steadily in one direction. In an AC circuit, it's constantly changing directions.

What is impedance?

It is the combined effect of resistance, inductive reactance, and capacitive reactance in an AC circuit.

What makes a fiber optic cable work?

Light propagation occurs when the refractive index of the core differs from the refractive index of the cladding

Select the correct statement regarding fiber optic cable

Multimode optical fibers (MMF) are vulnerable to modal dispersion

For guided mediums, insertion loss is dependent upon which of the following?

Number of connectors and splices Wire diameter Signal frequency

Determine the power in watts given the following: R = 100 Ohms , I = 10 A

P = I^2 x R, P = 10^2 x 100, = 10,000 W

Determine the power in watts given the following: R = 100 Ohms, V = 12 volts

P = V^2/R = 12^2/100 = 1.44 W

What is the difference between periodic and aperiodic signal?

Periodic signals are repeating, and aperiodic are not.

What is the significance of power (watts)?

Power measured in watts is energy in Joules expended over time. Power in a DC circuit is dissipated by the resistor in the form of heat. P(watts) = I^2 x R = V^2/R is used to determine the amount of power transferred to the resistor given either the voltage across or current through the resistor.

Which of the following determine the capacity of data in bits per second that can be supported over a transmission medium?

RF (EM) noise environment M'ary modulation and or M-ary line coding methods The coding communications medium itself

Describe the difference between impedance and resistance.

Resistance opposes the flow of current. IN a DC circuit, only resistance is experienced. However, in an AC circuit where voltage and current directions change over time, a time varying reactive component accompanies the resistive component within the circuit. Impedance is the combination of resistance and the time varying component of reactance.

UTP wire pairs use balanced signaling to eliminate undesired noise components.

Signals propagate on both wires but appear as mirror images of each other. Balanced signals implement noise cancelling techniques. The twisting of wire pairs minimizes cross talk.

Select the correct statement(s) regarding the polarization of RF waves.

The electric field of the RF wave determined the wave's polarization.

What is the power triangle.

The power triangle describes the relationship between apparent power (VA), real power (watts) and reactive power (VARs)

A carrier is a periodic wave that can be represented by either a sine or cosine wave. Once the carrier is combined with a message wave, the modulated carrier will have a frequency bandwidth that can be viewed in the frequency domain. True False

True

A switched circuit is one in which a user maintains the physical path through a network during the period of a call. Once the user's call is complete, the communications path is made available to other users. True False

True

In an unguided RF system, frequency reuse can be accomplished by transmitting two different signals at the same frequency, but with each EM signal having an orthogonal polarization from the other. True False

True

In unguided medium (free space), the electromagnetic (EM) signal wave spreads as it leaves the transmit antenna. Since the power of the EM signal resides at the surface area of the wave front, signal power is described as signal power density (i.e., watts per area). As the signal propagates away from the transmitter, power density decreases, and attenuation is experienced. True False

True

The time varying components of capacitance and inductance results in reactive power elements that can decrease power transfer. True False

True

When considering the impact of impulse noise, we find that it is more devastating to a digital communications link, than an analog one. Therefore error control methods should be used on all digital links. True False

True

When datagrams are exchanged using a connectionless virtual circuit, there is no guarantee that datagrams will arrive in proper sequence. It is left to the upper OSI layers to resequence received datagrams. True False

True

When determining the decibel value of the signal-to-noise ratio (SNR), both the signal and noise floor power must be referenced to the same power units (i.e., both referenced to 1 watt or 1 milliwatt) however SNR is a unitless ratio. True False

True

With error control, n-k bits are added to a dataword (k-bits in length) to create a codeword (n-bits in length) True False

True

In a DC circuit, use Ohm's Law to determine the current (I), given a voltage (V) of 3.5 volts and a resistance (R) of 240 ohms.

V = I x R, 3.5 = I x 240, I = V/R, I = 3.5/240 = 0.1458, = 14.58E-3 A

What is true regarding Ohm's Law?

a. Given a 10 Ohm resistive load, as voltage increases, current decreases. b. Given a 10 Ohm resistive load, as voltage increases, current increases. c. An increase in resistance causes an increase in current. d. None of the above b.

Select the correct statement(s) regarding amplitude modulation (AM). a. If the AM index is greater than 1, than overmodulation occurs leading to signal distortion. b. With AM, the message is captured as carrier frequency changes c. The AM modulated carrier bandwidth is always equal to the baseband bandwidth d. All of the above are correct

a. If the AM index is greater than 1, than overmodulation occurs leading to signal distortion.

Impedance is made up of resistance and reactance. Choose the correct statement.

a. Impedance describes only resistance, and reactance is an imaginary force that performs no work. b. Impedance in an AC circuit is equal to resistance plus reactance. c. Reactance values changes with time, while resistance does not change with time. d. Both B and C d. Both B and C.

__________ describes the electrical charge stored between parallel plates of opposite voltage polarity.

a. Inductance b. Reactance c. Capacitance d. Resistance c. Capacitance

Select the correct equation(s) for DC power.

a. P = IR b. P = I^2R c. P = V^2/R d. P = V cos (I) b and c

If both voltage and current waveforms have the same phase angles, they are in-phase to one another and the transfer of power from the source to the load is highly-efficient.

a. True b. False a.

Power factor (PF) can be determined for any DC or AC circuit.

a. True b. False a. True

Power in watts is related to voltage, resistance, and current.

a. True b. False a. True

The root mean square (RMS) method is used to determine the average AC values of instantaneous voltage, current, and power.

a. True b. False a. True

Select the correct statement(s) regarding DC and AC circuits.

a. Voltage and current levels change with time in a DC circuit. b. Voltage and current levels change with time in an AC circuit. c. DC voltages and currents are represented by sinusoidal waveforms. d. All of the above. b. Voltage and current levels change with time in an AC circuit.

Select the correct statement(s) regarding the difference between analog and digital signals. a. analog signals are comprised of an infinite number of amplitude and time slices. b. digital signals are only represented by discrete values of "0s" and "1s", and therefore can never convey analog information c. digital signals are more accurate than analog signals; this is why digital music sounds much better d. analog networks easily fit into the OSI Reference Model

a. analog signals are comprised of an infinite number of amplitude and time slices.

Select the correct statement(s) regarding impedance in a communications circuit. a. capacitance and inductance changes with signal frequency b. impedance is comprised of only resistive components c. the greater the reactance in a circuit, the less the overall resistance of within the circuit. d. all are correct statements.

a. capacitance and inductance changes with signal frequency

Identify the device that combines multiple time slots of frequency channels into an aggregate for transmission a. multiplexer b. modem c. repeater d. switch

a. multiplexer

An analog signal with a bandwidth of 36MHz is sampled at a frequency of 36,000,000 samples per second during the ADC (analog to digital conversion) process. What is the outcome of the received signal after the DAC (digital to analog conversion) process? a. The signal will have experienced aliasing b. The signal will not experience aliasing. c. the signal will perfectly represent the original pre-ADC analog signal d. none of the above describes the outcome

a. the signal will have experienced aliasing

Select the true statement regarding Amplitude Modulation (AM) a. when using DSB-LC AM modulation, the frequency bandwidth is fm b. both DSB-LC and DSB-SC have a frequency bandwidth of 2fm c. SSB modulation provides the highest quality AM signal. d. there are no true statements

b. Both DSB-LC and DSB-SC have a frequency bandwidth of 2fm

What is the difference between M-ary line coding and M-ary modulation. a. there is none b. M-ary line coding results in a baseband signal, while M-ary modulation results in a modulated digital signal c. M-ary line coding applies to digital baseband signals, while M-ary modulation applies to analog signals. d. Hartey's Law applies to M-ary line coding but not to M-ary modulation.

b. M-ary line coding results in a baseband signal, while M-ary modulation results in a modulated digital signal.

In selecting a line coding technique, we consider the need for receive clock synchronization, as well as the frequency bandwidth occupied by the resulting signal. What is true about the Manchester line coding technique. a. Manchester occupies less frequency spectrum (i.e., frequency bandwidth), than simpler line coding techniques such as NRZ b. Manchester ensures signal transitions for each bit sent, thus helping to ensure receive clock synchronization;however, it occupies twice the frequency bandwidth compared to NRZ. c. Manchester ensures greater receive clock synchronization and efficient bandwidth usage compared to NRZ d. there are no true statements listed above

b. Manchester ensures signal transitions for each bit sent, thus helping to ensure receive clock synchronization; however, it occupies twice the frequency bandwidth compared to NRZ.

What is the purpose of a transducer? a. They are used to transform potential energy (joules) into power (watts) b. Transducers are used to convert one form of signal energy into another form of signal energy. As an example, a microphone is an example of a transducer. c. Transducers are used to convert DC signals into an alternating (AC) signal d. None of the above

b. Transducers are used to convert one form of signal energy into another form of signal energy. As an example, a microphone is an example of a transducer.

Select the correct statement(s) regarding frequency modulation (FM) bandwidth. a. the more the carrier frequency is allowed to change frequencies, the smaller the modulated signal bandwidth. b. the larger the FM index, β, the larger the modulated signal bandwidth. c. as you increase kvco, you decrease modulated signal bandwidth d. all statements are correct

b. the larger the FM, index, β, the larger the modulated signal bandwidth.

Select the correct statement(s) regarding FDM and TDM. a. FDM and TDM are both identical in the way channels are aggregated; therefore their terms can be used interchangeably b. FDM aggregates channels by separating each by time slots, whereas TDM aggregates channels by frequency c. FDM separates channels in the frequency domain, whereas TDM separates time slots in the time domain. d. TDM requires guard channels in between information channels, whereas FDM does not require the use of guard channels

c. FDM separates channels in the frequency domain, whereas TDM separates time slots in the time domain.

Select the correct statement(s) regarding EM waves. a. EM depolarization enables frequency reuse b. RHCP and LHCP are EM waves that are considered linearly polarized c. RHCP and LHCP waves can be created by transmitting the same signal, separated by 90 degrees, using orthogonal polarizations. d. all of the statements are correct

c. RHCP and LHCP waves can be created by transmitting the same signal, separated by 90 degrees, using orthogonal polarizations.

Select the correct statement regarding acoustic and electrical signals. a. Acoustic wave propagate at the speed of light (3E8 m/s) b. Electrical waves depend upon the existence of air molecules in order to propagate c. Transducers are required to turn acoustic signals into an electrical signal. d. Acoustic signals are electric signals.

c. Transducers are required to turn acoustic signals into an electrical signal.

Select the correct statement(s) regarding symbol rate (baud rate) and bit rate (bits per second). a. a single logical bit can represent one or more symbols b. symbol rate is another term for bit rate - they are the same. c. a symbol can represent one or more logical bits. d. all are correct statements.

c. a symbol can represent one or more logical bits.

Identify the correct statement(s) regarding dedicated circuits. a. because call setup is not required, dedicated circuits are very efficient. b. dedicated and circuit switched concepts are identical c. dedicated circuits are used between specific locations where 24/7 connectivity is needed. d. all statements are correct

c. dedicated circuits are used between specific locations where 24/7 connectivity is needed.

Select the true statement(s) regarding a virtual circuit. a. both analog and digital networks take advantage of the virtual circuit concept b. virtual circuits require the assignment of dedicated physical links during network connection c. regarding the efficient use of physical links, virtual circuits are more efficient than analog circuits. d. both a and b are true statements

c. regarding the efficient use of physical links, virtual circuits are more efficient than analog circuits.

Select the correct statement(s) regarding optical signals. a. Optical signals are immune from radio frequency interference (RFI) b. Optical signal operate in the THz frequency range, which can support high data throughput c. Optical signals cannot be collected using RF antennas. d. All are correct statements.

d. All are correct statements

Analog information can be converted into digital data using techniques such as PCM (pulse code modulation). Select the correct statement(s) a. in order to convert an analog signal that consists of an infinite number of values, it must be sampled using the Nyquist sampling theorem. b. digitized analog signals always experience quantization loss. c. signal aliasing is experienced when sampling falls below the recommended Nyquist sampling rate. d. All of the above

d. All of the above

Select the best definition of a virtual connection or path. a. a virtual connection is one in which the physical path is shared by several users, but without their knowledge that the physical path is being shared b. a virtual connection is one in which a physical path is shared between the two users in a half-duplex manner (e.g., push to talk radios) c. a virtual connection is another term for a physical connection. d. a virtual connection is one in which the physical path is shared by several users, but without their knowledge that the physical path is being shared.

d. a virtual connection is one in which the physical path is shared by several users, but without their knowledge that the physical path is being shared.

Identify the ways a full duplex digital connection can be achieved by users. a. by separating transmit and receive directions using separate wires, cables, or channels in each direction. b. by using different modulation frequencies to separate transmit and receive directions c. by using different time slots to separate transmit and receive frequencies over a common medium d. all of the above

d. all of the above

Select the correct statement(s) regarding signal-to-noise ratio (SNR) a. SNR represents the ratio of receive power to noise floor power b. the decibel form of SNR is a unitless c. the correct equation for SNR in decibels is [SNR]dB = 10log10(S/N) d. all of the above

d. all of the above

What needs to be considered to ensure successful communications over guided or unguided mediums? a. determining the EM noise environment in which communications will take place b. understanding the frequency and frequency bandwidth limitations associated with the assigned communication frequencies c. matching modulation or line coding methods to the characteristics of communications being established d. all of the above

d. all of the above

Select the correct statement(s) regarding 4B5B. a. a four bit dataword is mapped to a 5 bit codeword; this results in only half of the possible codewords being mapped to legitimate datawords b. 4B5B means that only 80% of the codeword represents information, with 20% representing overhead. c. 4B5B avoids long string of logical "1s" and "0s" thus enabling use of simpler line coding techniques. d. all statements are correct.

d. all statements are correct

Select the correct statement(s) regarding AC signals. a. both current and voltage change over time b. AC can be represented as either periodic or aperiodic wave c. in a sinusoidal circuit, voltage may be out of phase from the current waveform d. all statements are correct.

d. all statements are correct

Select the correct statement(s) regarding DC circuits. a. Ohm's law states that voltage equals current multiplied by resistance b. power equals energy expended over time c. power in watts equals voltage multiplied by current d. all statements are correct

d. all statements are correct

Select the correct statement(s) regarding optical repeaters a. with an optical repeater the data signal must go through an OEO process b. unlike amplifiers, repeaters eliminate nosie from the signal c. repeaters can only be used on digital signals d. all statements are correct.

d. all statements are correct

Select the correct statement(s) regarding packet switching networks. a. all packets must contain source and destination addresses in a connectionless packet switching network. b. connection-oriented packet switching requires the establishment of a circuit between communicating nodes prior to the exchange of information. c. connection-oriented packet switching requires greater use of overhead bits compared to connectionless data exchanges. d. all statements are correct.

d. all statements are correct.

A _________ data compression technique results in some of the original data being lost.

lossy