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CHAPTER 6
Bandwidth Utilization:
Solutions to Odd-Numbered Review Questions and Exercises
Review Questions
1. Multiplexing is the set of techniques that allows the simultaneous transmission of
multiple signals across a single data link.
3. In multiplexing, the word link refers to the physical path. The word channel refers
to the portion of a link that carries a transmission between a given pair of lines.
One link can have many (n) channels.
5. To maximize the efficiency of their infrastructure, telephone companies have tradi-
tionally multiplexed analog signals from lower-bandwidth lines onto higher-band-
width lines. The analog hierarchy uses voice channels (4 KHz), groups (48 KHz),
supergroups (240 KHz), master groups (2.4 MHz), and jumbo groups (15.12
MHz).
7. WDM is common for multiplexing optical signals because it allows the multiplex-
ing of signals with a very high frequency.
9. In synchronous TDM, each input has a reserved slot in the output frame. This can
be inefficient if some input lines have no data to send. In statistical TDM, slots are
dynamically allocated to improve bandwidth efficiency. Only when an input line
has a slot’s worth of data to send is it given a slot in the output frame.
11. The frequency hopping spread spectrum (FHSS) technique uses M different car-
rier frequencies that are modulated by the source signal. At one moment, the signal
modulates one carrier frequency; at the next moment, the signal modulates another
carrier frequency.
Exercises
13. To multiplex 10 voice channels, we need nine guard bands. The required band-
width is then B = (4 KHz) × 10 + (500 Hz) × 9 = 44.5 KHz
15.
a. Group level: overhead = 48 KHz − (12 × 4 KHz) = 0 Hz.
b. Supergroup level: overhead = 240 KHz − (5 × 48 KHz) = 0 Hz.
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