---
title: "Short note: Optical fiber versus STP"
subject: "Data Communication"
chapter: 4
key: "semester_5/data_communication:optical-fiber-vs-stp"
source: https://www.bctengineer.com/q/semester_5/data_communication/optical-fiber-vs-stp
site: BCT Engineering
---

# Short note: Optical fiber versus STP

Data Communication · Chapter 4: Transmission Media

- Asked in: 2076 Asoj, 4 marks
- Video: [Lecture 11# Guided Media Made Easy | Twisted Pair, Coaxial & Optical Fiber](https://www.youtube.com/watch?v=2UQf1vxbTkc) — TecHno RayZ
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/data_communication/optical-fiber-vs-stp
- Whole chapter: https://www.bctengineer.com/md/semester_5/data_communication/chapter-4

## Question

Write a short note on optical fiber versus STP.

## Short answer

Optical fibre transmits light, providing immunity to EMI, extremely high bandwidth (Tbps), low attenuation (0.2-0.5 dB/km), and long spans tens of kilometres; it is costly and fragile. STP uses shielded copper pairs, limited to about 10 Gbps over 100 m, higher attenuation, but lower cost and easier to install.

## Answer

**Optical fibre** carries data as light pulses through a glass or plastic core. **STP (shielded twisted pair)** carries electrical signals over twisted copper pairs wrapped in a metal shield.

| Point | Optical fibre | STP |
|---|---|---|
| Signal | Light | Electrical |
| Bandwidth / data rate | Very high (Gbps to Tbps) | Limited (up to about 10 Gbps, short range) |
| Attenuation | Very low (0.2-0.5 dB/km) | High; repeaters every 100 m (LAN) to 2 km |
| Maximum distance | Up to tens of km | About 100 m for LAN use |
| EMI / crosstalk | Immune | Reduced by the shield, but not immune |
| Security | Hard to tap | Can be tapped |
| Cost | Higher (cable, connectors, laser/LED) | Lower |
| Installation | Skilled work, fragile | Easier, but heavy and stiff |
| Weight and size | Lighter and thinner | Heavier, thicker |

Fibre is chosen for backbones and long distance, while STP suits short, noisy-environment links at a lower cost.

## Check yourself

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

1. Which statement about interference is correct?
   A. Both are completely immune
   B. STP is immune but fibre is affected
   C. Fibre is immune to EMI; STP is reduced by the shield but not immune
   D. Fibre is affected, STP is partly shielded
   Answer: C. Light signals are not affected by electromagnetic fields; shield only reduces it. (Key point: EMI)

2. What is the typical maximum distance for each?
   A. Fibre about 100 m; STP tens of km
   B. Both about 100 m
   C. Fibre about 2 km; STP about 100 km
   D. Fibre tens of km; STP about 100 m for LAN use
   Answer: D. Fibre's very low attenuation allows long distances. (Key point: Distance)

3. Which gives the very low attenuation of 0.2-0.5 dB/km?
   A. STP
   B. Optical fibre
   C. Both equally
   D. Neither; both are about 3 dB/km
   Answer: B. STP has high attenuation and needs repeaters sooner. (Key point: Attenuation)

4. Which choice fits the comparison?
   A. STP for backbones; fibre for short links
   B. Fibre because it is cheaper and easier to install
   C. STP because it is immune to tapping
   D. Fibre for backbones and long distance; STP for short noisy links at lower cost
   Answer: D. Fibre costs more and needs skilled installation but suits backbones. (Key point: Cost and use)

## Related in Data Communication

- [Short note: STP versus UTP](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Autp-vs-stp) — Data Communication, chapter 4, asked 2×
- [Short note: Multi mode optical fiber](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Amultimode-fiber-short-note) — Data Communication, chapter 4
- [Optical fiber vs satellite transmission](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aoptical-fiber-vs-satellite) — Data Communication, chapter 4
- [Coaxial cable vs optical fiber](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Acoax-vs-fiber) — Data Communication, chapter 4
- [Optical fiber advantages over coax and twisted pair](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Afiber-advantages) — Data Communication, chapter 4, asked 3×

## Related in other subjects

- [Optical fiber and its advantages](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Aoptical-fiber-advantages) — Basic Electronics Engineering, chapter 5, asked 5×
- [Derive numerical aperture of optical fiber](https://www.bctengineer.com/question.md?key=semester_1%2Fengineering_physics%3Ana-derivation-optical-fiber) — Engineering Physics, chapter 6, asked 4×
- [Advantages of optical fiber over copper](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aoptical-fiber-advantages) — Instrumentation II, chapter 5, asked 3×
- [Optical fiber, NA, single vs multimode](https://www.bctengineer.com/question.md?key=semester_1%2Fengineering_physics%3Aoptical-fiber-na-acceptance-mode-comparison) — Engineering Physics, chapter 6