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Computer Networking

Ethernet Fiber-Optic Cables

Blue light passing over fibre optic cable
Photo by Compare Fibre on Unsplash

We would use fiber-optic over UTP cables for multiple reasons:

  • Longer maximum distance
  • Faster speed
  • No vulnerability to EMI (Electromagnetic Interference)
  • Better security (UTP emits a signal outside of the cable that can be copied)

How does fiber-optic transmission work?

Fiber-optic cables send light over glass fibers.

A light (optical transmitter) shines into the core.
To stay inside the core, the light is reflected off the cladding.

The outer jacket, strengthener and buffer are there to protect what is inside the cable (cladding and core) and also make it easier to manipulate.

This is a typical fiber-optic cable:

Photo by PawinG on pixabay

In one pair, one connector transmits data and the other receives data.
This is actually a single-mode cable (yellow jacket); multimode cables have an orange or aqua jacket.

Multimode and single-mode fiber-optic cables

There are two types of fiber-optic cables:

  • Multimode: multiple angles of light waves (LED light) are entering the core.
  • Single-mode: a single angle of light waves (Laser) is entering the core

Comparison between the two:

MultimodeSingle-mode
– Greater maximum distance than UTP cables
– But its maximum distance is still lower than single-mode’s (approximately 500m)
– Less expensive than single-mode		– Greater maximum distance than multimode (approximately 40km)
– More expensive than multimode

Using fiber-optic transmission with a switch

To use fiber with a switch, we need to have either a switch with built-in ports that support fiber-optic cables, or a switch with modular ports so that we can plug a SFP transceiver in, which can receive the fiber cable (see photo bellow).

Photo by Thomas Jensen on Unsplash. Modified.

SFP stands for “Small Form Pluggable”.
It is a hot-swappable device that we can plug into a device’s SFP port.

Cisco switches, for example, include these ports so that we can change them to Gigabit Ethernet interfaces or Fiber interfaces, depending on our needs.

Examples of SFP transceivers:

  • SFP : for Gigabit interfaces
  • SFP+ : for 10Gbps interfaces (but same size as SFP)

Resources:
Jeremy’s IT Lab: Free CCNA | Interfaces and Cables | Day 2 | CCNA 200-301 Complete Course
ICC: Singlemode Fiber and Multimode Fiber Optic Cable Differences