How many different types of physical media can you

How many different types of physical media can you
think of?
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Wires – Twisted Pair

Two insulated copper wires, twisted in helical (DNA) form.

Twisting reduces interference: canceling out electromagnetic
interference from external sources

Distance up to <5km, repeaters can extend this distance
cable with four
twisted pairs
11

Properties and Types of Twisted Pair

Bandwidth depends on distance, wire quality/ density

Cat 3 - 2 wires, 4 pairs in sheath, 16MHz

Cat 5 - 2 wires, 4 pair in sheath, more twists = less
interference, higher quality over longer distance, 100
MHz

Cat 8 – 2000 MHz
12
Don’t worry about this
unit for now, just higher
value is better!

Coaxial Cable (Co-ax)

Copper core with insulation, mesh, and sheath

Better shielding than twisted pair = higher speeds
over greater distances

Bandwidth approaches 1GHz

Still widely used for cable TV/Internet
13

Fibre Optics

Fibre has enormous bandwidth (THz) and tiny
signal loss

Data transmission over a fibre of glass

Common for high rates and long distances

e.g. backbone links between ISP facilities, Fibre-
to-the-Home (FTTH)
14

Transmission of Light Through Fibre

3 components: light source, transmission medium, detector

Semantics: light = 1, no light = 0 (basic binary system)

Signalling using LED’s or semiconductor lasers

A detector generates electrical pulse when light hits it

Refraction between air/silica boundary is compensated for by
design - total internal reflection
Light source
(LED, laser)
Photodetector
Light trapped by
total internal reflection
15

Fibre Optic Cables
Single-mode

Narrow core (10um), light can’t
even bounce around

Used with lasers for long distances,
e.g., 100km
Multi-mode

50um core, light can bounce

Used with LEDs for cheaper,
shorter distance links
16

Fibre Optic Connections

Connectors and Fibre Sockets (10-20% loss)

Mechanical Splice (10% loss)

Fusion (<1% loss)
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Examples: mechanical splice

Fibre Optic Networks

Fibre optic cable is a scalable network media - LAN,
WAN, long distances

Fibre optic cable networks can be organised either as a
ring or as a bus network (series of point to point
connections)
Fibre Optic Ring
18

Comparison of the properties of wires and fibre:
Comparison: Wires and Fibre
Property Wires Fibre
Distance Short (100s of m) Long (tens of km)
Bandwidth Moderate Very High
Security Easy to tap Hard to tap
Cost Inexpensive More Expensive
Convenience Easy to use Harder to use
19

Wireless Transmission

Mobile users requires a mobility enabled
network - contrast with the wired networks

Wireless networks can provide advantages even
in fixed location environments

Wireless data transmission networks have a
common basis - electromegnatic wave
propagation

Unlike previous media, wireless signals are
broadcasted over a region

Potential signal collisions – Need regulations
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