Ccna routing and Switching Complete Study Guide

Fiber Optic

Fiber-optic cabling has been around for a long time and has some solid standards. The 

cable allows for very fast transmission of data, is made of glass (or even plastic!), is very 

thin, and works as a waveguide to transmit light between two ends of the fiber. Fiber 

optics has been used to go very long distances, as in intercontinental connections, but it is 

---

Ethernet Cabling 

65

becoming more and more popular in Ethernet LAN networks due to the fast speeds avail-

able and because, unlike UTP, it’s immune to interference like cross-talk.

Some main components of this cable are the core and the cladding. The core will hold the 

light and the cladding confines the light in the core. The tighter the cladding, the smaller the 

core, and when the core is small, less light will be sent, but it can go faster and farther!

In Figure 2.19 you can see that there is a 9-micron core, which is very small and can be 

measured against a human hair, which is 50 microns.

f i g u r E   2 .19     Typical fiber cable 

Core

Cladding

Buffer

250

125

9

Dimensions are in um (10

–6

 meters). Not to scale. 

The cladding is 125 microns, which is actually a fiber standard that allows manufacturers 

to make connectors for all fiber cables. The last piece of this cable is the buffer, which is 

there to protect the delicate glass.

There are two major types of fiber optics: single-mode and multimode. Figure 2.20 shows 

the differences between multimode and single-mode fibers.

f i g u r E   2 . 2 0     Multimode and single-mode fibers

Cladding

Multimode fiber