Network PHY - Cabling
Cabling
Issues with cabling LANs
Types of equipment/choices
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Network PHY - Cabling
Media is a layer 1 device
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Network PHY - Cabling
Introduction
What are/is media?
What categories or types of media exist?
What happens to signals sent?
What are the common media technologies?
How do they compare?
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Network PHY - Cabling
A real life business example
An engineering company
Requires to network the site
Different logistical issues on the site
Engineering bay full of engineering equipment
and hence electrical interference
Several depts are remote (across a street)
Several depts are within one building
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Questions to ask
 Costs
 Performance including speed
 Reliability and fitness for purpose
 Scalability
 Several types of media may be chosen
 We would hope they are chosen for the right reasons
 For example, what should we choose for the
engineering bays described earlier?
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Answers to give
Many different solutions exist, but…
Cost, environment, legacy compatibility and
reliability are some of the key factors when
choosing media
Faster is often better – and not always more
expensive
Many older solutions have been superseded
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Media types
Guided media - twisted pair (UTP/STP),
coaxial cable (coax), optical fibre
Unguided media - radio, infrared, microwave
Point to point, where two devices share the
medium (intermediate repeaters or amplifiers)
Multipoint or broadcast where more than two
devices share the medium
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Problems with signals
Strength of the signal decreases with
distance. This gets worse at higher
frequencies.
Signal velocity depends on signal frequency,
so different frequency components arrive at
different times
Noise – thermal (hot electronics “hiss”), crosstalk (sometimes happens on phones), etc.
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Twisted pair (UTP & STP)
Digital signal repeaters required every 2 to 3
km
UTP is unshielded twisted pair; it is ordinary
copper telephone wire, the cheapest media for
LANs
STP is shielded twisted pair; less prone to
interference but more expensive and harder to
work with
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Network PHY - Cabling
Twisted pair (UTP & STP)
Insulated copper wires twisted together
Wires acts as a single communication link
Often used in telephone networks
Usually used within buildings
Comparatively cheap and easy to work with
Twists help to avoid cross-talk & noise effects
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Network PHY - Cabling
STP Cable
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Network PHY - Cabling
UTP Cable
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Cable Categories
Cat-1 was for telephones and ISDN
Cat-2 was used by IBM for 4Mbps Token-Ring
Cat-5e is used for 100Mbps Fast Ethernet and
ATM at 155Mbps, extends to 1000Mbps
(Gigabit Ethernet)
Cat-6 is for high speed networks using
200MHz-250MHz signalling
Cat-6a supports 500MHz signalling and thus
10Gbps throughput
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Crossover cable reminder
 CROSSOVER cables
connect 2 PC’s directly
together
 They cannot be used to
connect from a PC to a
hub or switch or router –
a different type of cable
is used for that - a
straight through
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But why a Crossover?
To connect similar devices
Eg PC to PC
Switch to Switch
Switch to hub
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Coaxial cable
Better frequency characteristics, higher data
rates, and more immune to interference than
twisted pair
Uses: Television distribution,
Long distance telephone transmission,
Short run computer I/O channels,
LANs
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Coaxial Cable
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Thinnet Vs Thicknet
10BASE2 50 Ohm Coaxial Cable
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10BASE5 Thicknet cable
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Network PHY - Cabling
Optical fibre
Data rates of 2Gbps or more, over tens of
kilometres
Low attenuation (decrease of signal amplitude
over length of a link)
Not susceptible to electromagnetic
interference or cross-talk
Used for long haul, metropolitan and rural
trunk lines, secure LANs
See IEEE 802.8 standards for more
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Fibre connectors
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Fibre Optic Cabling
Fibre can be
manufactured in 40Km
lengths.
Some fibre-based
systems carry 100Gbps
signalling.
Using Wave-Division
Multiplexing, terabit data
rates are possible.
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Satellite microwave
Provides point to point or point to multi-point
connectivity
Common for TV broadcasting
Long distance telephone transmission
Public and private business networks
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Broadcast radio
Omnidirectional – broadcasts all around
Simple antenna, not like satellite microwave
Antenna alignment allowed to be imprecise
Good for data networks where some or all
stations may be mobile
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Infrared
Line of sight is needed
No radio-frequency spectrum allocation is
needed
Provides point-to-point connectivity (adds security?)
Good for short distances
No radio interference problems (but sunlight probs)
Speed: from 300Kbps to 4Mbps (IRDA), with
IR laser systems over 100Mbps
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Conclusion
Media types have been introduced and
discussed
There are choices of how we use our cables
Useful Links:
1. http://customcable.ca/cat5-vs-cat6/
2. http://www.howtogeek.com/70494/what-kind-ofethernet-cat-5e6a-cable-should-i-use/
3. http://en.wikipedia.org/wiki/Optical_fiber
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