---
title: "Multiplexing: definition and applications"
subject: "Data Communication"
chapter: 6
key: "semester_5/data_communication:mux-define-why"
source: https://www.bctengineer.com/q/semester_5/data_communication/mux-define-why
site: BCT Engineering
---

# Multiplexing: definition and applications

Data Communication · Chapter 6: Multiplexing and Spreading

- Asked in: 2079 Baisakh, 2 marks; 2074 Chaitra, 3 marks; 2072 Chaitra, 2 marks; 2072 Kartik, 4 marks; 2068 Chaitra, 4 marks (asked 5 times)
- Video: [Types of Multiplexing | FDM TDM WDM | Analog Digital | Computer Networks](https://www.youtube.com/watch?v=WXof7bg_Zys) — Dr. Ankit Verma
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/data_communication/mux-define-why
- Whole chapter: https://www.bctengineer.com/md/semester_5/data_communication/chapter-6

## Question

What is multiplexing and why do we need it? Mention its applications.

## Short answer

Multiplexing allows multiple signals to simultaneously share a single transmission link via a multiplexer/demultiplexer pair, efficiently utilizing high-bandwidth media and reducing infrastructure costs. It is needed for economic bandwidth usage. Applications include telephone backbone trunks (TDM), radio/TV broadcasting (FDM), cellular networks, optical WDM, DSL, and cable TV.

## Answer

**Multiplexing** is a set of techniques that allows many signals to share a single communication link at the same time. At the sender a multiplexer (MUX) combines n input lines into one link, and at the receiver a demultiplexer (DEMUX) separates them back into n output lines.

#### Why it is needed
- A link such as fibre, coaxial cable or a microwave channel has far more bandwidth than one user needs. Without multiplexing, most of it is wasted.
- Laying a separate cable for each connection is very costly; sharing one link cuts the cost of media, installation and maintenance.
- Better utilisation of bandwidth and equipment.
- Fewer physical links give a simpler network design.

#### Main techniques
- **FDM** (frequency division): each signal uses its own frequency band.
- **TDM** (time division): each signal uses the link in its own time slot.
- **WDM** (wavelength division): each signal uses its own light wavelength in fibre.
- **CDM** (code division): each signal uses its own code.

#### Applications
- Telephone trunks carry thousands of voice calls using FDM or TDM (T1/E1, SONET/SDH).
- Radio and TV broadcasting (AM, FM, TV channels share the air by FDM).
- Cellular networks (FDMA, TDMA in GSM, CDMA).
- Optical fibre backbones and internet service providers (WDM/DWDM).
- DSL, which separates voice and data by frequency using a splitter, and cable TV with many channels on one coaxial cable.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why is multiplexing needed?
   A. A link has far more bandwidth than one user needs, and separate cables are costly
   B. To reduce bandwidth of fibre
   C. To make each user slower
   D. To avoid using demultiplexers
   Answer: A. Sharing one link improves utilisation and cuts cost. (Key point: Why multiplexing)

2. Which technique gives each signal its own light wavelength in fibre?
   A. FDM
   B. TDM
   C. WDM
   D. CDM
   Answer: C. WDM uses wavelengths. (Key point: WDM)

3. Which is an application of FDM?
   A. AM/FM radio channels sharing the air
   B. Single-user cable
   C. Hard-disk storage
   D. Keyboard input
   Answer: A. Radio and TV stations share the air by FDM. (Key point: Application)

## Related in Data Communication

- [Applications of Fourier series](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Afourier-series-applications) — Data Communication, chapter 3
- [Why the Fourier transform is needed](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Awhy-fourier-transform-needed) — Data Communication, chapter 3, asked 2×
- [FDM bandwidth for 10 voice channels](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Afdm-10-voice-channels) — Data Communication, chapter 6
- [Minimum Hamming distance; find k and n](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Amin-hamming-k-n) — Data Communication, chapter 8

## Related in other subjects

- [Why do we need DFT](https://www.bctengineer.com/question.md?key=semester_7%2Fdigital_signal_analysis_and_processing%3Awhy-need-dft) — Digital Signal Analysis and Processing, chapter 7, asked 6×
- [Why do we need FFT](https://www.bctengineer.com/question.md?key=semester_7%2Fdigital_signal_analysis_and_processing%3Awhy-need-fft) — Digital Signal Analysis and Processing, chapter 7, asked 2×
- [Need for multiplexing and WDM](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Amultiplexing-need-wdm) — Telecommunications, chapter 3
- [Operator overloading: need and definition](https://www.bctengineer.com/question.md?key=semester_3%2Fobject_oriented_programming%3Aoperator-overloading-why-define) — Object Oriented Programming, chapter 5, asked 3×