Ch 1 - P1 Telephony

Question 1

Name the 3 basic components of a telecommunications transmission system.

Answer 1

1. Source of energy
2. Medium to carry the energy
3. Receiving Device

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Question 2

What is the purpose of an analog telephone?

Answer 2

To convert sound waves into electrical analog signals that can be transmitted over much longer distances than sound waves can travel.

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Question 3

Early telephones were designed to match the frequencies used in human speech, which included frequencies from 50 Hz to 12 kHz.

Answer 3

False, Although speech may contain frequencies from 50 Hz to 12 kHz, early studies found that good quality speech intelligibility could be obtained if only the frequency range of about 300 Hz to 3400 Hz was actually transmitted. Consequently, this is the frequency band that early telephone circuits were designed to support.

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Question 4

What is the most significant property of a digital signal?

Answer 4

The most significant property of a digital signal is that at any time it can take on only a value from a discrete set of values.

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Question 5

What 3 steps are sued to convert an analog signal to a digital signal?

Answer 5

1. Filtering
2. Sampling.
3. Quantizing/companding

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Question 6

What type of device converts electrical energy back into sound energy?

Answer 6

Receiver

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Question 7

What does the maximum transmission of electrical power occur in a telephone line?

Answer 7

When a transmitting device and a receiving device have the same load resistance or the same impedance.

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Question 8

How does impedance differ from resistance?

Answer 8

Both are measured in ohms, but impedance has both a magnitude and a phase component.

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Question 9

What is the preferred impedance for private line circuits and trunks?

Answer 9

600 ohms

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Question 10

What is the preferred impedance for CO switching system line circuits?

Answer 10

900 ohms

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Question 11

When is an echo perceptible during a long distance phone call?

Answer 11

When part of the transmitted signal is sent or reflected back to the originating end.

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Question 12

What causes part of a signal to be sent back or reflected to the originating end?

Answer 12

Impedance mismatch between the transmission line and the receiver.

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Question 13

What principal elements contribute to loss and phase distortion at voice frequencies?

Answer 13

• Conductor resistance
• Mutual capacitance of the cable pair

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Question 14

How does increasing the frequency affect the speed of transmission through cable pairs?

Answer 14

Increasing the frequency increases the speed of transmission.

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Question 15

Increasing the frequency to increase the speed of transmission does not noticeably affect speech intelligibility.

Answer 15

True. Increasing the frequency to increase the speed of transmission does not noticeably, affect speech intelligibility, but it can have a great affect on data transmission.

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Question 16

What is the purpose of placing load coils along a cable?

Answer 16

To improve speech transmission quality

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Question 17

How do load coils improve the quality of speech transmission?

Answer 17

By compensating for the capacitance of a cable pair

By reducing the capacitive current loading in the range of audio frequencies

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Question 18

What is the most common distance between loading points for D loading?

Answer 18

= 1.37 km (4495 ft)

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Question 19

What is the most common distance between loading points for H loading?

Answer 19

= 1.83 km (6004 ft)

Question 20

What types of signals are blocked by loading coils?

Answer 20

Analog high fidelity and digital signals

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Question 21

How do loading coils affect data transmission?

Answer 21

Load coils adversely affect data transmission.

Question 22

What determines the upper cutoff frequency of a loading coil?

Answer 22

Loading coil spacing determines the upper cutoff frequency.

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Question 23

Name 3 common interface options for IP telphony.

Answer 23

1. IP telephone
2. Computer with IP telephony software and microphone/ speaker or USB handset
3. Multifunctional devices with a wireless receiver

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Question 24

IP telephony software is only operational when the computer is running.

Answer 24

True. IP telephony software is only operational when the computer is running.

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Question 25

Name 3 common implementation options for IP telephony architecture.

Answer 25

1. Separate Lines
2. One line for everything using a dual-port IP telephone or a soft telephone
3. Wireless connection using ASs to connect the IP telephone

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Question 26

Although using a dual-port telephone or softphone may sound like an attractive option, what are the possible drawbacks?

Answer 26

A single cable carrying all information reduces flexibility and redundancy.

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Question 27

How many telecommunications outlets or connectors are recommended for each individual work area?

Answer 27

2

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Question 28

Both horizontal cables at the work area location should be considered cables that support data apllications.

Answer 28

True. While one cable may be associated with voice and the other with data, both should be considered cables that support data applications.

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Question 29

What is used to provide uninterrupted power to the telephone set?

Answer 29

Power over the Ethernet (PoE)