TRUE/FALSE
1. Little data communication is carried over voice-grade telephone lines.
ANS: F
2. The word "keying" is still used to denote digital modulation schemes.
ANS: T
3. ASK is rarely used for data communications.
ANS: T
4. Information capacity is proportional to bandwidth.
ANS: T
5. Information capacity is independent of noise.
ANS: F
6. "Baud rate" is the same as bits per second.
ANS: F
7. A "mark" is a binary one.
ANS: T
8. "Space" is another term for bandwidth.
ANS: F
9. FSK is slow, but "robust".
ANS: T
10. FSK makes efficient use of available bandwidth.
ANS: F
11. FSK is used extensively in high-frequency radioteletype transmission.
ANS: T
12. PSK is typically faster than FSK.
ANS: T
13. "Dibit" is another term for PSK.
ANS: F
14. PSK is typically DPSK.
ANS: T
15. QPSK is typically DQPSK.
ANS: T
16. Digital amplitude modulation is called QAM.
ANS: F
17. QAM uses PSK.
ANS: T
18. A "constellation diagram" shows the "symbols" used in QAM.
ANS: T
19. CCITT is now ITU-T.
ANS: T
20. Equalization compensates for phase and frequency distortions in a channel.
ANS: T
21. Signal complexity compensates for low S/N during transmission.
ANS: F
22. Receiver equalization requires a "training sequence" be sent at startup.
ANS: T
23. 54 kbps is about the maximum speed you can get from a telephone line modem.
ANS: T
24. High-speed modems cannot do data compression.
ANS: F
25. High-speed modems cannot do error correction.
ANS: F
26. MNP4 is an error-correction protocol.
ANS: T
27. V.42 is a data-compression scheme.
ANS: F
28. A computer is a DTE.
ANS: T
29. A MODEM is a DCE.
ANS: T
30. EIA-232D is the same as RS-232C.
ANS: T
31. RS-232 describes a parallel port protocol.
ANS: F
32. The response to RTS is DSR.
ANS: F
33. RTS and CTS provide a "handshake" between a DTE and a DCE.
ANS: T
34. +10 volts on an RS-232 control line is a HIGH or TRUE level.
ANS: T
35. +12 volts on an RS-232 signal line is a binary ONE.
ANS: F
36. A line is active when it is "asserted".
ANS: T
37. "Smart" MODEMS are initialized with a string of "AT" commands.
ANS: T
38. Twisted-pair telephone wire is not capable of more than about 4 kHz of bandwidth.
ANS: F
39. DSL carries high-speed data over twisted-pair telephone wire.
ANS: T
40. CATV cables only carry signals one way: from the head-end to the subscriber.
ANS: F
41. Fiber-optic CATV cables carry analog signals.
ANS: T
42. Typically, a NIC is required to interface a PC to a cable modem.
ANS: T
43. A cable modem is always on.
ANS: T
44. A DSL connection is always on.
ANS: T
45. A cable modem shares the channel with other users.
ANS: T
46. A DSL connection shares the loop with other subscribers.
ANS: F
47. ADSL Lite is faster than standard ADSL.
ANS: F
48. ADSL Lite requires a splitter at the subscriber end.
ANS: F
49. In practice, both ADSL Lite and a cable modem have comparable data rates.
ANS: T
MULTIPLE CHOICE
1. FSK stands for:
a. | Full-Shift Keying | c. | Full-Signal Keying |
b. | Frequency-Shift Keying | d. | none of the above |
ANS: B
2. PSK stands for:
a. | Pulse-Signal Keying | c. | Phase-Signal Keying |
b. | Pulse-Shift Keying | d. | Phase-Shift Keying |
ANS: D
3. QAM stands for:
a. | Quadrature Amplitude Modulation | c. | Quadrature Amplitude Marking |
b. | Quadrature Amplitude Masking | d. | none of the above |
ANS: A
4. In the equation I = ktB, I is measured in:
a. | amperes | c. | bits |
b. | amperes per second | d. | bits per second |
ANS: C
5. In the equation C = 2Blog2M, M is the:
a. | margin of noise | c. | number of possible states per symbol |
b. | modulation index | d. | maximum number of symbols per second |
ANS: C
6. An "eye pattern" shows a good channel when:
a. | the eye is maximally open | c. | the eye is half open |
b. | the eye is maximally closed | d. | the eye alternately opens and closes |
ANS: A
7. What you see in an eye pattern is the effect of:
a. | too many bits high | c. | intermodulation distortion |
b. | too many bits low | d. | intersymbol interference |
ANS: D
8. High-frequency radioteletype systems commonly use:
a. | FSK | c. | PSK |
b. | AFSK | d. | QAM |
ANS: A
9. Instead of a single bit, a QPSK symbol contains:
a. | a byte | c. | a dibit |
b. | 4 bits | d. | a Q-bit |
ANS: C
10. To reduce the need for linearity, p/4 DQPSK uses:
a. | angles of 0, 90, 180, and 270 degrees | c. | angles of p/4, 2p/4, 3p/4, and 4p/4 |
b. | angles of 45, 135, 225, and 315 degrees | d. | double phase-shift angles |
ANS: B
11. For QAM, a "constellation diagram" shows:
a. | location of symbols in "symbol space" | c. | effects of noise on symbols |
b. | separation of symbols in "symbol space" | d. | all of the above |
ANS: D
12. For QAM, the two dimensions of its symbol space are:
a. | amplitude and frequency | c. | frequency and phase angle |
b. | amplitude and phase angle | d. | I-bits and Q-bits |
ANS: B
13. The specs of the old Bell type 103 modem were:
a. | 300 bps, full-duplex, FSK | c. | 1200 bps, full-duplex, FSK |
b. | 600 bps, full-duplex, FSK | d. | 1200 bps, half-duplex, FSK |
ANS: A
14. ITU is an abbreviation for:
a. | International Telephony Unit | c. | International Telecommunications Union |
b. | International Telephony Union | d. | International Telecommunications Units |
ANS: C
15. The ITU is under the auspices of:
a. | CCITT | c. | IEEE |
b. | the U.N. | d. | ANSI |
ANS: B
16. High-speed modems equalize the line to compensate for:
a. | noise and interference |
b. | uneven phase and frequency response |
c. | low SNR |
d. | inconsistent bit rates at either end of channel |
ANS: B
17. The bits sent to allow equalization are called:
a. | Gaussian bits | c. | a training sequence |
b. | random bits | d. | a random sequence |
ANS: C
18. The V.90 standard is issued by:
a. | the EIA | c. | the ITU |
b. | the TIA | d. | the ISO |
ANS: C
19. MNP2, MNP3, MNP4, and MNP10 are all:
a. | data-compression schemes | c. | both a and b |
b. | error-correction protocols | d. | none of the above |
ANS: B
20. MNP5 and V.42 bis are both:
a. | data-compression schemes | c. | both a and b |
b. | error-correction protocols | d. | none of the above |
ANS: A
21. In RS-232, flow control is done using:
a. | RTS/CTS handshake | c. | both a and b |
b. | XON/XOFF characters | d. | none of the above |
ANS: C
22. The official name for RS-232C is:
a. | RS-232C | c. | ISO-232C/D |
b. | EIA-232D | d. | ANSI-232C |
ANS: B
23. In RS-232, a modem would be:
a. | a DTR | c. | a DCE |
b. | a DSR | d. | a DTE |
ANS: C
24. In RS-232, a personal computer would be:
a. | a DTR | c. | a DCE |
b. | a DSR | d. | a DTE |
ANS: D
25. On a DB-9 RS-232 connector, signal ground is pin:
a. | 1 | c. | 5 |
b. | 3 | d. | 7 |
ANS: C
26. On a DB-25 RS-232 connector, signal ground is pin:
a. | 1 | c. | 5 |
b. | 3 | d. | 7 |
ANS: D
27. The minimum lines required for RS-232 are:
a. | TD and RD | c. | TD, RD, DSR, and signal ground |
b. | TD, RD, and signal ground | d. | TD, RD, RTS, CTS, and signal ground |
ANS: B
28. Hardware flow control uses:
a. | XON and XOFF | c. | RTS and CTS |
b. | TD and RD | d. | DSR and DCD |
ANS: C
29. Software flow control uses:
a. | XON and XOFF | c. | RTS and CTS |
b. | TD and RD | d. | DSR and DCD |
ANS: A
30. Which voltage represents a binary zero on an RS-232 data pin:
a. | +15 volts | c. | +9 volts |
b. | +12 volts | d. | all of the above |
ANS: D
31. DSL stands for:
a. | Data Signal Line | c. | Digital Subscriber Line |
b. | Digital Signal Line | d. | Double-Speed Loop |
ANS: C
32. ADSL stands for:
a. | Asynchronous DSL | c. | Analog DSL |
b. | Asymmetrical DSL | d. | All DSL |
ANS: B
33. In a CATV system, HFC stands for:
a. | Head Frequency Control | c. | Hybrid Fiber-Coax |
b. | Hybrid Frequency Control | d. | Hybrid Fiber Control |
ANS: C
34. In a CATV system, CMTS stands for:
a. | Cable Modem Terminal Server | c. | Cable Modem Terminal System |
b. | Cable Modem Transmission System | d. | Cable Modem Transmission Server |
ANS: A
35. A "splitter" at the subscriber end is not required for:
a. | Any DSL scheme | c. | ADSL Lite |
b. | ADSL | d. | none of the above |
ANS: C
COMPLETION
1. RTS means Request To ____________________.
ANS: Send
2. The response to RTS is ____________________.
ANS: CTS
3. FSK stands for Frequency-Shift ____________________.
ANS: Keying
4. DSR stands for ____________________ Set Ready.
ANS: Data
5. QAM stands for ____________________ Amplitude Modulation.
ANS: Quadrature
6. The number of symbols per second is called the ____________________ rate.
ANS: baud
7. The 2 bits of information in a QPSK symbol is called a ____________________.
ANS: dibit
8. QPSK uses ____________________ different phase angles.
ANS: four
9. DPSK stands for ____________________ PSK.
ANS: Delta
10. The QAM amplitude-phase combinations are shown with a ____________________ diagram.
ANS: constellation
11. ITU stands for International _________________________ Union.
ANS: Telecommunications
12. In QAM modems, ____________________ coding adds extra bits to improve performance on a noisy line.
ANS: Trellis
13. ____________________ is used in a high-speed modem to compensate for uneven frequency and phase response on a line.
ANS: Equalization
14. The maximum allowed speed for a modem on a dial-up line is about ____________________ bps.
ANS: 54k
15. The nominal maximum speed on an RS-232 cable is ____________________ bps.
ANS: 20k
16. In RS-232, the ____________________ line is asserted when the analog carrier from another modem is being received.
ANS:
CD
DCD
RLSD
17. Between hardware flow control and software flow control, ____________________ flow control is preferred.
ANS: hardware
18. A voltage higher than ____________________ volts should be considered a high on an RS-232 receiver.
ANS: 3
19. A ____________________ modem cable is used to connect two DTEs via their serial ports.
ANS: null
20. ADSL stands for ____________________ DSL.
ANS: Asymmetrical
21. A typical CATV system is organized as a ____________________ network.
ANS: tree
22. In a CATV system using cable modems, a ____________________ is used to put several channels of data onto a fiber-optic backbone.
ANS: CMTS
23. ____________________ is the process of synchronizing transmitted data from cable modems to a CMTS.
ANS: Ranging
24. ____________________ systems send high-speed data over a POTS line while sharing the line with dial-up service.
ANS: ADSL
25. The ____________________ version of ADSL does not require a splitter at the subscriber end.
ANS: lite
26. ____________________ modulation divides the line bandwidth into many narrow bands called tones or bins for ADSL.
ANS: DMT
27. A DSLAM is a DSL Access ____________________.
ANS: Multiplexer
SHORT ANSWER
SHORT ANSWER
1. Calculate the bits per second capacity of a system sending 1000 symbols per second with 16 possible states per symbol.
ANS:
4000
2. How many points will be on the constellation diagram of a QAM system using 8 phase angles and 2 amplitude levels?
ANS:
16
3. A CATV system has 100 cable-modem customers sharing a single channel with a data rate of 36 Mbps. If half the modems are active at any given time, what bit rate can a customer expect?
ANS:
720 kbps
4. A DMT system uses 4.3-kHz bins on a 1-MHz cable. Approximately how many bins are there?
ANS:
230
5. Assuming a maximum symbol rate of 400 per second, how many possible states must a symbol have to achieve a data rate of 1200 bps?
ANS:
8
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