---
title: "Compare FDM, WDM and TDM"
subject: "Data Communication"
chapter: 6
key: "semester_5/data_communication:compare-fdm-wdm-tdm"
source: https://www.bctengineer.com/q/semester_5/data_communication/compare-fdm-wdm-tdm
site: BCT Engineering
---

# Compare FDM, WDM and TDM

Data Communication · Chapter 6: Multiplexing and Spreading

- Asked in: 2068 Chaitra, 4 marks
- 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/compare-fdm-wdm-tdm
- Whole chapter: https://www.bctengineer.com/md/semester_5/data_communication/chapter-6

## Question

Compare FDM, WDM and TDM.

## Short answer

FDM (analog) shares a medium by frequency bands; WDM (optical) does the same with wavelengths; TDM (digital) shares by time slots, one channel transmitting at a time. FDM and WDM send all channels simultaneously; TDM requires synchronization. FDM uses guard bands and modulators; WDM uses prisms/grating; TDM uses framing bits. FDM is for radio/cable, WDM for fibre, TDM for digital telephony.

## Answer

| Point | FDM | WDM | TDM |
|---|---|---|---|
| Full form | Frequency division multiplexing | Wavelength division multiplexing | Time division multiplexing |
| Signal type | Analog | Optical (light) | Digital |
| Sharing by | Frequency bands | Light wavelengths | Time slots |
| Medium | Coax, radio, twisted pair | Optical fibre | Any (wire, fibre, radio) |
| Simultaneity | All channels at once | All channels at once | One channel at a time, in turn |
| Needs | Modulators, filters, guard bands | Prism / grating MUX and DEMUX | Synchronisation, framing bits |
| Interference | Crosstalk, intermodulation | Very low | Timing jitter, slot synchronisation |
| Examples | Radio/TV, cable TV | DWDM backbone | T1/E1, SONET |

WDM is essentially FDM applied to light, and TDM is the basis of digital telephony.

## Check yourself

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

1. What does each technique share?
   A. FDM: time slots; TDM: frequency
   B. FDM: frequency bands; WDM: light wavelengths; TDM: time slots
   C. All share time slots
   D. FDM: wavelengths; WDM: frequency bands
   Answer: B. FDM shares by frequency, WDM by wavelength, TDM by time. (Key point: Sharing method)

2. Which statement is correct?
   A. FDM and WDM send all channels at once; TDM sends one at a time in turn
   B. TDM sends all channels at once
   C. All three send one channel at a time
   D. FDM sends one at a time
   Answer: A. FDM and WDM channels are simultaneous; TDM channels take turns. (Key point: Simultaneity)

3. Which technique is used on optical fibre?
   A. FDM
   B. TDM only
   C. WDM
   D. None
   Answer: C. WDM uses prism or grating MUX and DEMUX on fibre. (Key point: Medium)

4. TDM needs which of the following?
   A. Guard bands and modulators
   B. Synchronisation and framing bits
   C. Prisms
   D. PN codes
   Answer: B. TDM needs synchronisation and framing bits. (Key point: Needs)

## Related in Data Communication

- [Compare FDM and FHSS](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Afdm-vs-fhss) — Data Communication, chapter 6
- [Multiplexing; synchronous vs asynchronous TDM](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Amux-compare-sync-async-tdm) — Data Communication, chapter 6, asked 6×

## Related in other subjects

- [Comparison of FDM, TDM and WDM](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Amultiplexing-fdm-tdm-wdm) — Telecommunications, chapter 3, asked 2×
- [TDM vs FDM for voice; E1 and T1 hierarchies](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Atdm-fdm-voice-e1-t1) — Communication Systems, chapter 5
- [FDM and TDM with block diagrams](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Amultiplexing-fdm-tdm-block) — Telecommunications, chapter 3
- [Short note: FDM vs TDM](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Ashort-note-fdm-vs-tdm) — Communication Systems, chapter 5