Chapter 5 – Multiplexing (Forouzan, Data Communications & Networking 4e)

27 question-and-answer flashcards covering definitions, techniques, calculations, and applications of FDM, WDM, synchronous TDM, and statistical TDM as presented in Chapter 5 of Forouzan’s Data Communications & Networking (4th Edition).

What is meant by "bandwidth utilization" in data communications?

The wise use of available bandwidth to achieve goals such as efficiency (via multiplexing) or privacy/anti-jamming (via spreading).

Define multiplexing.

A set of techniques that allows the simultaneous transmission of multiple signals across a single data link when the link’s bandwidth exceeds the bandwidth needs of the individual devices.

In a multiplexed system, what is the difference between a path and a channel?

Path refers to the physical link; channel refers to a portion of that link allocated to a specific signal.

Name the three major categories of multiplexing introduced in the chapter.

Frequency-Division Multiplexing (FDM), Wavelength-Division Multiplexing (WDM), and Time-Division Multiplexing (TDM).

What is a guard band in FDM and why is it used?

An unused portion of bandwidth placed between adjacent FDM channels to prevent signal overlap and interference.

Is FDM an analog or digital technique?

Analog; it combines analog signals.

How much minimum bandwidth is needed to multiplex 5 channels of 100 kHz each with 10 kHz guard bands between them?

540 kHz (5 × 100 kHz + 4 × 10 kHz).

List two common applications of FDM.

1) Television broadcasting over coaxial cable (6 MHz per TV channel). 2) AM/FM radio broadcasting (AM: 530–1700 kHz, 10 kHz per station; FM: 88–108 MHz, 200 kHz per station).

What does WDM stand for and what medium does it use?

Wavelength-Division Multiplexing; it multiplexes optical signals over fiber-optic cable.

Which fiber-optic standard often employs WDM?

SONET (Synchronous Optical Network).

What distinguishes TDM from FDM/WDM in terms of signal type?

TDM is a digital multiplexing technique that interleaves time slots from multiple low-rate digital channels onto a higher-rate digital link.

Complete the statement: In synchronous TDM, the link data rate is times faster than an individual input line and each slot duration is correspondingly .

n times faster; 1/n as long (where n = number of input lines).

State the three data-rate management strategies used when input rates differ in synchronous TDM.

Multilevel multiplexing, multiple-slot allocation, and pulse stuffing.

What is multilevel multiplexing?

Combining lower-rate multiplexed groups into higher-rate groups to match different input data rates.

Explain pulse stuffing.

Adding extra dummy bits or bytes to slower input streams so that all inputs appear at the same rate to the multiplexer.

Why are framing bits needed in synchronous TDM?

To allow the receiver to synchronize with frame boundaries; usually one bit per frame alternating 1 and 0.

How does statistical TDM improve bandwidth efficiency compared with synchronous TDM?

It dynamically allocates slots only to active input lines, so each frame contains fewer slots than the number of lines, reducing wasted capacity.

In statistical TDM, why must slot size keep a reasonable ratio of data bytes to address bytes?

To keep transmission efficient; the overhead (address) should be small relative to the data payload.

Give two applications of synchronous TDM.

Digital telephone hierarchy (DS/T-Lines, E-Lines) and 2nd-generation cellular systems (30 kHz bands shared by 6 users).

Give two applications of statistical TDM.

Digital TV broadcasting and data transmission over LAN or WAN links.

Example: Three 4-kHz voice channels are shifted to 20–24 kHz, 24–28 kHz, 28–32 kHz and combined. What multiplexing technique is used?

Frequency-Division Multiplexing (FDM).

Example: Four channels each send 100 bytes/s, 1 byte per channel per frame. What is the frame size, frame rate, and link bit rate?

Frame size = 4 bytes (32 bits); frame rate = 100 frames/s; link bit rate = 100 × 32 = 3200 bps.

Example: A TDM multiplexer combines four 100 kbps lines using 2-bit slots. What is the frame rate and overall bit rate?

Frame rate = 50,000 frames/s; each frame = 8 bits, so bit rate = 50,000 × 8 = 400 kbps.

What problem can arise in synchronous TDM when some input lines are idle, and what visual representation shows it?

Empty or unused slots waste bandwidth; this appears as blank positions in the TDM frame diagram.

Which multiplexing technique uses prisms to separate and combine channels?

Wavelength-Division Multiplexing (WDM).

Summarize the main purpose of multiplexing.

To share the excess bandwidth of a single physical link among multiple signals, increasing efficiency and reducing cost.