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TDMM Flash Cards > Ch 1 - P 1 - Digital Signals > Flashcards

Ch 1 - P 1 - Digital Signals Flashcards

1
Q

What is the most significant property of a digital signal?

A

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.

TDMM: Page 1-29

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2
Q

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

A
  1. Filtering
  2. Sampling
    #. Quantizing / companding
    TDMM: Page 1 - 29
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3
Q

Why is the analog filtered before it is sampled?

A

To limit its frequency content

TDMM: Page 1-29

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4
Q

What sampling rate is used to faithfully reproduce the analog signal during the conversion process?

A

A rate that is at least twice the highest frequency component of the analog signal

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5
Q

What is quantizing?

A

Assigning each sampled value a discrete level that approximates the analog signal at the sampling instant

TDMM: Page 1-30

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6
Q

What is companding?

A

Non-uniform mapping between the analog sampled value to an assigned digital level

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7
Q

Name the 2 forms of companding that are in current use.

A
  1. A-Law
  2. Mu-Law

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8
Q

What type of companding is used in the United States, Canada, and Japan?

A

Mu-Law

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9
Q

What type of companding is used in Europe?

A

A-Law

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10
Q

A-Law and Mu-Law are compatible.

A

False. Although they perform similar functions, A-Law and Mu-Law are not compatible.

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11
Q

What term is used to describe the three-step process for converting an analog signal into a digital signal?

A

Pulse code modulation (PCM)

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12
Q

What is used to encode speech signals at data rates lower than 64 kb/s?

A

Data signal processing

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13
Q

What data rates can be used by ADPCM?

A

40,32,24 and 16 kb/s

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14
Q

What device is used to convert speech to a digital signal and its subsequent decoding to speech?

A

Codec

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15
Q

At what rates can vocoders transmit speech?

A

8 to 2.4 kbs

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16
Q

What do lower bit rates typically imply about a signal’s quality?

A

That the signal quality is degraded

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17
Q

What process involves combining binary data from several different sources into a single composite bit stream?

A

Time Division Multiplexing (TDM)

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18
Q

What is the purpose of TDM?

A

To increase the information-carrying capacity of the digital telecommunications channel. TDMM: Page 1-31

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19
Q

How is TDM accomplished?

A

By predetermined (deterministic) interleaving of samples from different voice channels along with one or more bits for control purposes to make up a frame.

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20
Q

What is the most popular form of TDM?

A

Statistical TDM

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21
Q

In the DS1 format, the digital data from __ speech channels is combined for transmission over a single transmission channel.

A

In the DS1 format, the digital data from 24 speech channels is combined for transmission over a single transmission channel.

TDMM: Page 1-31

22
Q

What is the data rate for the DS1 format?

A

1.544 Mb/s

TDMM: Page 1-32

23
Q

Describe the CEPT PCM-30 format.

A

In the CEPT PCM-30 format, the digital data from 30 speech channels is combined for transmission over a single transmission channel.

TDMM: Page 1-32

24
Q

What is the data rate for CEPT PCM-30 format?

A

2.048 Mb/s

TDMM: Page 1-32

25
Q

What term is used to describe the process of reconstituting the individual channels from the composite signal?

A

Demultiplexing

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26
Q

What is a channel bank?

A

Multiplexing and demultiplexing equipment

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27
Q

What stages of multiplexing contain A/D conversion?

A

Only the first order multiplexing stage (T1 and E1)

TDMM: Page 1-32

28
Q

In the United States, how many T1 frames are needed to create a superframe?

A

12

TDMM: Page 1-33

29
Q

In Europe, how many E1 frames are needed to create a multiframe?

A

16

TDMM: Page 1-33

30
Q

What is the basic unit of digital data?

A

Bit

TDMM: Page 1-33

31
Q

True or False – A sequence of binary pulses consisting of 1s and 0s is the optimum format for transmitting digital data over balanced-twisted pair cables.

A

False. A sequence of binary pulses consisting of ones and zeros is not the optimum format for transmitting digital data over balanced twisted-pair cables.

TDMM: Page 1-33

32
Q

What is the final step in the encoding process?

A

The modification of the shape and pattern of pulses to achieve more efficient transmission

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33
Q

What is the line-encoding technique designed to do?

A

Eliminate the DC component

Improve timing recovery

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34
Q

What encoding technique is used for T1 carriers?

A

Bipolar alternate mark inversion (AMI)

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35
Q

What type of encoding allows signal transition to occur in the middle of every bit interval?

A

Manchester encoding

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36
Q

What term is used to describe the rate at which a signal can change states?

A

Baud

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37
Q

What transmission method is used for ISDN (basic rate)?

A

2B1Q

TDMM: Page 1-35 Table 1.10

38
Q

What transmission method is used for ISDN (primary rate)?

A

Bipolar

TDMM: Page 1-35, Table 1.10

39
Q

What transmission method is used for HDSL?

A

2B1Q

TDMM: Page 1-35, Table 1.10

40
Q

What transmission method is used for 10Base-T?

A

Manchester

TDMM: Page 1-35, Table 1.10

41
Q

What is the encoding rate for ISDN (basic rate)?

A

160 kb/s

TDMM: Page 1-35, Table 1.10

42
Q

What is the encoding rate for ISDN (primary rate)?

A

1.544 Mb/s

TDMM: Page 1-35, Table 1.10

43
Q

What is encoding rate for HDSL?

A

2 x 784 kb/s

TDMM: Page 1-35, Table 1.10

44
Q

What is the encoding rate for 10BASE-T?

A

10 Mb/s

TDMM: Page 1-35, Table 1.10

45
Q

What is a QAM signal?

A

A signal composed of two sinusoidal carriers, each having the same frequency but differing in phase by one quarter of a cycle

TDMM: Page 1-37

46
Q

Which QAM sinusoid is the equivalent of a sine wave?

A

I signal

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47
Q

Which QAM sinusoid is the equivalent of a cosine wave?

A

Q signal

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48
Q

What type of modulation does DMT use?

A

Multicarrier modulation

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49
Q

How can data rates be adjusted with DMT?

A

By increasing the number of sub-bands and by carrying the number of bits carried in each sub-band

TDMM: Page 1-37

50
Q

Which line application uses 8B/1Q4 PAM 5 encoding?

A

1000BASE-T

TDMM: Page 1-37

TDMM Flash Cards (7 decks)

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