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Understanding Data Communications: From Fundamentals to Networking

Gilbert Held

Chapter 8

Basic Transmission Devices: Line Drivers, Modems, and Service Units - all with Video Answers

Educators

Chapter Questions

Problem 1

What is the general relationship between pulse width and data rate?

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Problem 2

What is the general relationship between the transmission rate and cable length on an RS-232 serial connection?

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Problem 3

Discuss an application for a line driver.

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Problem 4

Describe the basic signal conversion performed by modems.

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01:49

Problem 5

What is a carrier signal? By itself, does it convey any information? Why?

Arpit Gupta
Arpit Gupta
Numerade Educator

Problem 6

How can the characteristics of a carrier signal be altered?

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Problem 7

What is the difference between a bit per second and a baud? When can they be equivalent? When are they not equivalent?

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Problem 8

What is the Nyquist relationship and why does it require modem designers to develop multilevel phase-shift keying modulation schemes for modems to operate at high data rates?

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Problem 9

Why does full-duplex transmission enhance transmission efficiency?

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Problem 10

How could you use a reverse channel? What is the difference between a reverse channel and a secondary channel?

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Problem 11

How does a modem obtain a multiport capability?

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Problem 12

Describe the operation of a security modem.

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Problem 13

What is the function of the modem handshaking process?

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Problem 14

What is the difference between a local analog modem test and a digital loopback modem test?

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Problem 15

Assume that two modems connected to a leased line have both local and digital loop-back self-testing features. If communications were disabled, discuss the tests you would perform to determine if the line or one or both modems caused the communications failure.

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Problem 16

What does the term 'Bell System' compatibility mean when discussing the operational characteristics of a modem?

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Problem 17

If an originate mode modem transmits a mark at $f_1$ and a space at $f_2$ and receives a mark at $f_3$ and a space at $f_4$, what would be the corresponding frequencies of an answer mode modem to ensure communications compatibility?

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Problem 18

Discuss the conventional utilization of originate and answer mode modems.

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Problem 19

Why is it more likely than not that an American using his or her portable personal computer in Europe would not be able to communicate with a computer located in Europe?

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Problem 20

What does the signal constellation pattern of a modem represent? What is the normal relationship between the signal constellation pattern and the susceptibility of a modem to transmission impairments?

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Problem 21

Discuss the difference between Trellis coded modulation and conventional quadrature amplitude modulation with respect to the density of the signal constellation and the susceptibility of a modem employing each modulation technique to transmission impairments?

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Problem 22

Why are Bell System 212 -type modems operating at 1200 bps sometimes compatible with V. 22 modems, whereas at other times they are incompatible?

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Problem 23

Why are Bell System 202 type modems incompatible with ITU-T V. 23 modems?

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Problem 24

Discuss the compatibility of a ITU-T V. 26 modem employing a pattern $A$ phase change with a similar modem using the pattern B phase change.

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01:08

Problem 25

Explain why the V. 29 signal constellation pattern forms a mirror image.

Andy Chen
Andy Chen
Numerade Educator

Problem 26

What is echo cancellation and why is its use important for modem operations on the switched network?

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Problem 27

Besides a faster operating rate, name another advantage associated with the use of a V. 32 bis modem over a V. 32 modem.

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Problem 28

Compare the features of a V. 32 bis modem to a V. 33 modem.

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Problem 29

What is the purpose of the V. 34 modem supporting signaling methods below 300 Hz ?

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Problem 30

Discuss two potential problems when using a V. 34 modem that could limit its ability to operate at 33.6 kbps .

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Problem 31

How can the asymmetrical transmission capability of a V. 34 modem improve its performance?

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Problem 32

How does a reduction in quantization noise effect the transmission capability of a modem?

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Problem 33

Why is a V. 90 modem limited to a 56 kbps data rate in one direction?

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Problem 34

Why is flow control important when using error detection and correction?

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Problem 35

Describe two flow control methods.

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Problem 36

What is the difference between V. 42 and V. 42 bis?

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Problem 37

Discuss the reason why a cable modem can transmit data at a higher operating rate than a modem designed for use on the switched network when both modems use the same general modulation method.

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Problem 38

How can an ADSL modem use the same portion of frequency for upstream and downstream transmission?

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Problem 39

Describe two differences between an ADSL modem and a G.lite modem.

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Problem 40

Describe two DSU functions in addition to network synchronization.

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Problem 41

xDescribe two CSU functions.

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Problem 42

How does a DSU perform network synchronization?

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Problem 43

Discuss the relationship of the DSU to the CSU with respect to loopbacks.

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