TRUE/FALSE
1. A telephone from 1930 could not work on today's public switched telephone network.
ANS: F
2. The public switched telephone network is changing from an all analog to a mostly digital system.
ANS: T
3. A LATA is a local calling area.
ANS: T
4. A feature of the public switched telephone system is that calls cannot be "blocked".
ANS: F
5. Telephones connect to the central office via trunk lines.
ANS: F
6. The telephone switching hierarchy is being replaced by a "flat" network topology.
ANS: T
7. Most local loops still use copper wire.
ANS: T
8. A "twisted-pair" is twisted to minimize "crosstalk".
ANS: T
9. The wires in a local loop are called TIP and GND.
ANS: F
10. In a local loop, the red wire is positive.
ANS: F
11. In a local loop, the TIP wire is positive.
ANS: T
12. Local loops can carry voice signals in only one direction at a time.
ANS: F
13. Local loops carry DC current.
ANS: T
14. Local loops carry signaling information.
ANS: T
15. Loading coils allow high-speed data loads to be carried on a local loop.
ANS: F
16. Typically, when a phone is on hook, a voltage of 48 volts appears across it.
ANS: T
17. When a telephone is off hook, the DC voltage across it can drop substantially from its on-hook value.
ANS: T
18. The DC resistance of a telephone is about 2000 ohms.
ANS: F
19. When a telephone is on hook, the DC current through it is in the range of 20 to 80 mA.
ANS: F
20. Touch-Tone is a registered trademark of AT&T.
ANS: T
21. DTMF is the same as Touch-Tone.
ANS: T
22. DTMF uses sets of 3 tones.
ANS: F
23. The technology to "dial" telephone numbers was invented in 1893.
ANS: T
24. A crosspoint switch allows any incoming line to be connected to any outgoing line.
ANS: T
25. The central office uses 24 volts AC at 20 hertz to cause a telephone to ring.
ANS: F
26. The local-loop is full-duplex.
ANS: T
27. Telephones usually contain a hybrid coil or an equivalent circuit.
ANS: T
28. To allow for "sidetone", a hybrid coil should be slightly unbalanced.
ANS: T
29. The signal levels in analog telephone systems have increased substantially over the past 100 years.
ANS: F
30. The signal levels in modern analog telephone systems are still based on 19th-century technology.
ANS: T
31. To allow multiplexing, the bandwidth of voice-grade telephone signals is deliberately restricted.
ANS: T
32. The net gain of a telephone system must be greater than 0 dB for an acceptable signal level.
ANS: F
33. Too much gain in a telephone system causes "singing".
ANS: T
34. Echo suppressors prevent oscillations on long-distance telephone circuits.
ANS: T
35. Echo suppressors can be switched off by a subscriber's equipment.
ANS: T
36. C-message weighting increases the bandwidth of a local loop.
ANS: F
37. The reference level for measuring noise in a telephone system is 10–12 Watts.
ANS: T
38. In a telephone system, signal strength is given relative to the zero transmission loss point.
ANS: T
39. TDM is being replaced by the newer FDM technology in telephone systems.
ANS: F
40. DS-1 can be used to carry digital data that did not originate as a voice signal.
ANS: T
41. When using DS-1 to carry data, it is common to use each channel to carry 64 kbps.
ANS: F
42. Digital carriers up to T3 can use copper wires.
ANS: F
43. A DS-1C signal carries twice as many channels as a DS-1 signal.
ANS: T
44. A DS-1C signal uses twice the bit rate of a DS-1 signal.
ANS: F
45. "Stuff" bits are used to compensate for differences in clock rates.
ANS: T
46. Every "in-channel" signal is also an "in-band" signal.
ANS: F
47. Common-channel signaling is being replaced by the more modern MF signaling.
ANS: F
48. Common-channel signaling reduces opportunities for stealing telephone service.
ANS: T
49. ADSL is faster than ISDN.
ANS: T
50. B-ISDN is a slower version of standard ISDN.
ANS: F
MULTIPLE CHOICE
1. DTMF stands for:
| a. | Digital Telephony Multiple Frequency | c. | Dual-Tone Multifrequency |
| b. | Dial Tone Master Frequency | d. | Digital Trunk Master Frequency |
ANS: C
2. PSTN stands for:
| a. | Public Switched Telephone Network | c. | Primary Service Telephone Network |
| b. | Private Switched Telephone Network | d. | Primary Service Telephone Numbers |
ANS: A
3. POTS stands for:
| a. | Private Office Telephone System | c. | Primary Operational Test System |
| b. | Primary Office Telephone Service | d. | Plain Old Telephone Service |
ANS: D
4. LATA stands for:
| a. | Local Access and Transport Area | c. | Local Area Telephone Access |
| b. | Local Access Telephone Area | d. | Local Area Transport Access |
ANS: A
5. A LATA is a:
| a. | a local calling area | c. | a way of accessing a tandem office |
| b. | a type of digital local network | d. | a way of accessing a central office |
ANS: A
6. Central offices are connected by:
| a. | local loops | c. | both a and b |
| b. | trunk lines | d. | none of the above |
ANS: B
7. Local loops terminate at:
| a. | a tandem office | c. | a central office |
| b. | a toll station | d. | an interexchange office |
ANS: C
8. Call blocking:
| a. | cannot occur in the public telephone network |
| b. | occurs on the local loop when there is an electrical power failure |
| c. | occurs only on long-distance cables |
| d. | occurs when the central office capacity is exceeded |
ANS: D
9. In telephony, POP stands for:
| a. | Post Office Protocol | c. | Power-On Protocol |
| b. | Point Of Presence | d. | none of the above |
ANS: B
10. The cable used for local loops is mainly:
| a. | twisted-pair copper wire | c. | coaxial cable |
| b. | shielded twisted-pair copper wire | d. | fiber-optic |
ANS: A
11. FITL stands for:
| a. | Framing Information for Toll Loops | c. | Framing In The Loop |
| b. | Fiber In the Toll Loop | d. | Fiber-In-The-Loop |
ANS: D
12. Loading coils were used to:
| a. | increase the speed of the local loop for digital data |
| b. | reduce the attenuation of voice signals |
| c. | reduce crosstalk |
| d. | provide C-type conditioning to a local loop |
ANS: B
13. DC current flows through a telephone:
| a. | when it is on hook | c. | as long as it is attached to a local loop |
| b. | when it is off hook | d. | only when it is ringing |
ANS: B
14. The range of DC current that flows through a telephone is:
| a. | 20 mA to 80 mA | c. | 2 mA to 8 mA |
| b. | 200 mA to 800 mA | d. | 20 mA to 80 mA |
ANS: D
15. The separation of control functions from signal switching is known as:
| a. | step-by-step switching control | c. | common control |
| b. | crossbar control | d. | ESS |
ANS: C
16. The typical voltage across a telephone when on-hook is:
| a. | 48 volts DC | c. | 90 volts DC |
| b. | 48 volts, 20 hertz AC | d. | 90 volts, 20 hertz AC |
ANS: A
17. The typical voltage needed to "ring" a telephone is:
| a. | 48 volts DC | c. | 90 volts DC |
| b. | 48 volts, 20 hertz AC | d. | 90 volts, 20 hertz AC |
ANS: D
18. The bandwidth of voice-grade signals on a telephone system is restricted in order to:
| a. | allow lines to be "conditioned" | c. | allow signals to be multiplexed |
| b. | prevent "singing" | d. | all of the above |
ANS: C
19. VNL stands for:
| a. | voltage net loss | c. | via net loss |
| b. | volume net loss | d. | voice noise level |
ANS: C
20. Signal loss is designed into a telephone system to:
| a. | eliminate reflections | c. | improve signal-to-noise ratio |
| b. | prevent oscillation | d. | reduce power consumption |
ANS: B
21. The reference noise level for telephony is:
| a. | 1 mW | c. | 1 pW |
| b. | 0 dBm | d. | 0 dBr |
ANS: C
22. The number of voice channels in a basic FDM group is:
| a. | 6 | c. | 24 |
| b. | 12 | d. | 60 |
ANS: B
23. Basic FDM groups can be combined into:
| a. | supergroups | c. | jumbogroups |
| b. | mastergroups | d. | all of the above |
ANS: D
24. In telephone system FDM, voice is put on a carrier using:
| a. | SSB | c. | PDM |
| b. | DSBSC | d. | PCM |
ANS: A
25. PABX stands for:
| a. | Power Amplification Before Transmission |
| b. | Private Automatic Branch Exchange |
| c. | Public Automated Branch Exchange |
| d. | Public Access Branch Exchange |
ANS: B
26. SLIC stands for:
| a. | Single-Line Interface Circuit | c. | Subscriber Line Interface Card |
| b. | Standard Line Interface Card | d. | Standard Local Interface Circuit |
ANS: C
27. In DS-1, bits are "robbed" in order to:
| a. | provide synchronization | c. | cancel echoes |
| b. | carry signaling | d. | check for errors |
ANS: B
28. "Bit-stuffing" is more formally called:
| a. | compensation | c. | justification |
| b. | rectification | d. | frame alignment |
ANS: C
29. ISDN stands for:
| a. | Integrated Services Digital Network | c. | Integrated Services Data Network |
| b. | Information Services Digital Network | d. | Information Systems Digital Network |
ANS: A
30. Basic ISDN has not been widely adopted because:
| a. | it took to long to develop |
| b. | it is too slow |
| c. | it has been surpassed by newer technologies |
| d. | all of the above |
ANS: D
31. ADSL stands for:
| a. | All-Digital Subscriber Line | c. | Allocated Digital Service Line |
| b. | Asymmetrical Digital Subscriber Line | d. | Access to Data Services Line |
ANS: B
32. Compared to ISDN, internet access using ADSL is typically:
| a. | much faster | c. | much more expensive |
| b. | about the same speed | d. | none of the above |
ANS: A
COMPLETION
1. A ____________________ is a local calling area.
ANS: LATA
2. Central offices are connected together by ____________________ lines.
ANS: trunk
3. One central office can be connected to another through a ____________________ office.
ANS: tandem
4. With 7-digit phone numbers, ____________________ thousand telephones can connect to a central office.
ANS: ten
5. Call ____________________ is when it becomes impossible for a subscriber to place a call due to an overload of lines being used.
ANS: blocking
6. New ____________________ switching equipment uses TDM to combine signals.
ANS: digital
7. Most local loops still use ____________________ copper wire.
ANS: twisted-pair
8. As compared to a hierarchical network, a ____________________ network never needs more than one intermediate switch.
ANS: flat
9. ____________________ coils were used to reduce the attenuation of voice frequencies.
ANS: Loading
10. In a twisted-pair telephone cable, the red wire is called ____________________.
ANS: ring
11. In a twisted-pair telephone cable, the green wire is called ____________________.
ANS: tip
12. Of the red and green 'phone wires, the ____________________ wire is positive with respect to the other.
ANS: green
13. A telephone is said to have ____________________ the line when the central office sends it dial tone.
ANS: seized
14. The ____________________ functions are provided by a SLIC.
ANS: BORSCHT
15. A ____________________ coil prevents loss of signal energy within a telephone while allowing full-duplex operation over a single pair of wires.
ANS: hybrid
16. In a crosspoint switch, not all ____________________ can be in use at the same time.
ANS: lines
17. The old carbon transmitters generated a relatively ____________________ signal voltage.
ANS: large
18. The generic term for Touch-Tone® signaling is ____________________.
ANS: DTMF
19. A ____________________ line provides more bandwidth than a standard line.
ANS: conditioned
20. In the telephone system, amplifiers are called ____________________.
ANS: repeaters
21. An echo ____________________ converts a long-distance line from full-duplex to half-duplex operation.
ANS: suppressor
22. ____________________ weighting is an attempt to adjust the noise or signal level to the response of a typical telephone receiver.
ANS: C-message
23. In FDM telephony, the modulation is usually ____________________.
ANS:
SSB
SSBSC
24. In FDM telephony, ____________________ bands separate the channels in a group.
ANS: guard
25. Because of "bit robbing", a channel in a DS-1 frame allows only ____________________ kbps when used to send digital data.
ANS: 56
26. A ____________________ is a group of 12 DS-1 frames with signaling information in the sixth and twelfth frames.
ANS: superframe
27. In DS-1C, ____________________ bits are used to compensate for differences between clock rates.
ANS: stuff
28. Busy and dial tone are referred to as ____________________ signals because they use the same pair of wires as the voice signal.
ANS: in-channel
29. SS7 is the current version of _________________________ signaling.
ANS: common-channel
30. SS7 is a ____________________-switched data network.
ANS: packet
31. In ISDN, the ____________________ channel is used for common-channel signaling.
ANS: D
32. In ISDN, the ____________________ channels are used for voice or data.
ANS: B
33. Terminal equipment especially designed for ISDN is designated ____________________ equipment.
ANS: TE1
34. The A in ADSL stands for ____________________.
ANS: asymmetrical
35. In ADSL, the speed from the network to the subscriber is ____________________ than the speed in the opposite direction.
ANS:
greater
faster
SHORT ANSWER
1. For a certain telephone, the DC loop voltage is 48 V on hook and 8 V off hook. If the loop current is 40 mA, what is the DC resistance of the local loop?
ANS:
1000 ohms
2. For a certain telephone, the DC loop voltage is 48 V on hook and 8 V off hook. If the loop current is 40 mA, what is the DC resistance of the telephone?
ANS:
200 ohms
3. Which two DTMF tones correspond to the digit "1"? (Use the table in the text.)
ANS:
697 Hz and 1209 Hz
4. Calculate the dB of VNL required for a channel with a 3 ms delay.
ANS:
1 dB
5. If a telephone voice signal has a level of 0 dBm, what is its level in dBrn?
ANS:
90 dBrn
6. A telephone test-tone has a level of 80 dBrn at a point where the level is +5dB TLP. If C-weighting produces a 10-dB loss, what would the signal level be in dBrnc0?
ANS:
65 dBrnc TLP
0 comments:
Post a Comment