---
title: "FDDI features"
subject: "Computer Networks and Security"
chapter: 3
key: "semester_7/computer_networks_and_security:fddi-features"
source: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/fddi-features
site: BCT Engineering
---

# FDDI features

Computer Networks and Security · Chapter 3: Data Link Layer

- Asked in: 2072 Chaitra; 2074 Chaitra, 4 marks (asked 2 times)
- Video: [FDDI (Fiber Distributed Data Interface)](https://www.youtube.com/watch?v=AQkn7c4QT1Q) — BTech Days
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/fddi-features
- Whole chapter: https://www.bctengineer.com/md/semester_7/computer_networks_and_security/chapter-3

## Question

List the features of FDDI. (Short note: FDDI.)

## Short answer

FDDI is a 100 Mbps dual-ring fibre LAN with token passing, self-healing, up to 100 km, and 500 stations. It uses 4B/5B encoding, early token release, and supports synchronous/asynchronous traffic with Class A and B stations.

## Answer

**FDDI (Fiber Distributed Data Interface)** is a high-speed LAN/MAN standard (ANSI X3T9.5) that uses fibre optic cable in a **dual counter-rotating ring** topology at 100 Mbps with token passing.

#### Features
1. **Speed:** 100 Mbps data rate.
2. **Medium:** multimode fibre (62.5/125 micron), also supports copper (CDDI, UTP/STP).
3. **Topology:** two counter-rotating rings, primary and secondary. The secondary is a backup that is used when the primary breaks, giving **fault tolerance** (self-healing by wrapping the ring).
4. **Distance:** up to 100 km ring length and up to 2 km between stations, with up to 500 stations (1000 connections).
5. **Access method:** timed **token passing**. A station captures the token to send frames and releases a new token after transmission (early token release).
6. **Reliability and security:** immune to EMI, hard to tap.
7. **Station types:** Class A (dual attachment, on both rings) and Class B (single attachment, via a concentrator).
8. **Encoding:** 4B/5B with NRZI.
9. **Supports** synchronous (time-sensitive) and asynchronous traffic.
10. **Frame size** up to 4500 bytes.

Used as a backbone for LANs and campus networks, now replaced by Gigabit Ethernet.

## Check yourself

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

1. What topology does FDDI use, and why?
   A. Single bus, for cheap wiring
   B. Dual counter-rotating rings, so the secondary ring gives fault tolerance
   C. Star with a hub, for collision avoidance
   D. Single ring, for faster speed
   Answer: B. The secondary ring is a backup used when the primary breaks; the ring wraps to self-heal. (Key point: FDDI topology)

2. Which pair correctly gives FDDI's data rate and access method?
   A. 10 Mbps, CSMA/CD
   B. 16 Mbps, token ring
   C. 100 Mbps, timed token passing
   D. 1 Gbps, polling
   Answer: C. FDDI runs at 100 Mbps over fibre with timed token passing. (Key point: FDDI speed and access)

3. Which statement about FDDI station classes is correct?
   A. Class A attaches to both rings; Class B attaches singly via a concentrator
   B. Class A attaches via a concentrator; Class B attaches to both rings
   C. Both classes attach to the secondary ring only
   D. Class A is copper only; Class B is fibre only
   Answer: A. Class A is dual attachment (both rings); Class B is single attachment through a concentrator. (Key point: Station classes)