Teacher Page 24 File

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Transcript Teacher Page 24 File

24 Wired Transmission
24 Wired Transmission
• This is about the method used to
actually transmit or send data
• That means actual wires or cables
• You need to know three types
• And the advantages/disadvantages
• You might think wires are boring
• But imagine life without Sky TV,
the web and computer networks…
24 Wired Transmission
UTP Cable
Co-axial
Fibre Optic
24 Wired Transmission
• When it comes to cabling, you might
think ‘who cares’ ?
• But networks are hugely important today
• So designers take care to pick the right
cable to build networks
• Key issues are cost and speed, meaning
how much data the cable can carry
• The goal is to reduce latency
• That’s the delay in between sending and
receiving data
24 Wired Transmission
STP
Cable
Network
Co-axialTV
Digital
Backbone
Fibre Optic
Backgrounder
– Cables & Digital Data
24
Wired Transmission
• Information such as computer data and
telephone calls can be converted into
electrical signals
• These can be carried through wires that
conduct electricity, such as copper cables
• But the info can also be converted into light
signals and transmitted by optical fibre
• Let’s have a quick look at how that works…
Backgrounder
– Data Means Bits
24
Wired Transmission
Remember that ‘digital’ data means 1s & 0s…
Binary
Bit is a 0 or a 1
Byte is 8 bits
01100001
Backgrounder
– Electric Signals
24
Wired Transmission
That digital data can be shown as a ‘square’ wave, like on & off…
0
1
1
0
0
0
0
1
And those 1s and 0s could be high & low voltage on a wire…
But electric signals must have no interference to get clean 1s & 0s
24 Wired Transmission
UTP
• UTP is the cable used for
for most LANs, like our
network in school
• It’s called Unshielded Twisted Pair
• Inside are several pairs of copper wire
• They’re twisted to stop electrical
interference
• UTP cable is popular for LANs because it is
cheap and can carry lots of data
• There’s also Shielded Twisted Pair (STP)…
24 Wired Transmission
UTP Unshielded
STP Shielded
24 Wired Transmission
Co-Axial
• You’ll find ‘coax’
round the back of
at
your satellite TV box
• It has two copper conductors separated
by an insulator
• That enables it to work at higher data
rates than twisted pair
• It can be used for networks but costs
more than UTP and is harder to install
because it’s not as flexible
24 Wired Transmission
Fibre Optic
• Strands of glass as thin as
hair that carry data as light
• Lots of fibres are bundled together
to form cables
• Cheaper than traditional copper
telephone wire
• T1 lines give local connection
• T3 lines form Internet backbone
24 Wired Transmission
24 Wired Transmission
SUBMARINE
24 Wired
CABLE
MAP
Transmission
Backgrounder
– Electrical Interference
24
Wired Transmission
Optical signals can be transmitted so far due to how light travels…
Backgrounder
– Optical Data
24
Wired Transmission
• A laser at one end of the pipe switches on and off to
send each bit.
• Modern fiber systems with a single laser can transmit
billions of bits per second -- the laser can turn on and
off several billions of times per second.
• The newest systems use multiple lasers with different
colors to fit multiple signals into the same fiber.
24 Wired Transmission
STP Cable
Network
Co-axial
Digital TV
Fibre Optic
Backbone
24 Wired Transmission
24 Wired Transmission