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Wired Media

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... by motors, power lines, televisions, copiers, fluorescent lights, or broadcast signals from radio or TV towers Unlike thermal noise, impulse noise is variable ... – PowerPoint PPT presentation

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Title: Wired Media


1
Wired Media
2
Transmission Flaws
  • Transmission signals are adversely affected by a
    number of factors two of which we will discuss
  • Noise
  • Attenuation

3
Noise
  • Electrical interference causes spurious
    electrical currents in the media that interfere
    with the signal
  • Humans perceive noise during a telephone call
    call as static
  • Three sources of noise
  • Thermal noise
  • Impulse noise
  • Crosstalk

4
Effect of Noise
5
Thermal Noise
  • Caused by the thermal agitation of electrons in
    metal
  • Present in all electronic equipment and forms an
    upper bound on the potential capacity of a media
  • Also called white noise
  • Can be reduced by cooling media and equipment but
    this isnt usually practical

6
Impulse Noise
  • Caused by electromagnetic interference (EMI) and
    radio frequency interference (RFI)
  • Electromagnetic interference (EMI)
  • Interference that may be caused by motors, power
    lines, television, copiers, fluorescent lights,
    or other sources of electrical activity
  • Radiofrequency interference (RFI)
  • Interference that may be generated by motors,
    power lines, televisions, copiers, fluorescent
    lights, or broadcast signals from radio or TV
    towers Unlike thermal noise, impulse noise is
    variable and is difficult to plan for
  • Care must be taken when cables are laid to avoid
    sources of EMI/RFI

7
Crosstalk
  • Crosstalk is interference caused in one wire by
    the legitimate signal in an adjacent wire
  • Crosstalk can be detected as background
    conversations during phone calls
  • Crosstalk is particularly a problem at the
    connectors that connect cables to network devices

8
Attenuation
  • Loss of signal strength as transmission travels
    away from source
  • Analog signals may be boosted by an amplifier,
    which increases not only voltage of a signal but
    also noise accumulated
  • Digital signals may be boosted by a repeater
    which regenerates the original signal without
    noise if possible

9
Attenuation and Thermal Noise
10
Repeaters
  • Repeater
  • Device used to regenerate a signal

11
Effect of Increased Bandwidth
  • Increasing the bandwidth of a signal increases
    throughput by increasing the number of bits that
    can be represented in a given time
  • At higher frequencies the signal attenuates
    faster
  • Smaller bits may be wiped more easily by noise
  • Cant turn bandwidth up beyond what media can
    support
  • Higher bandwidth signals travel shorter distances
    on a given medium

12
Wired Media Types
13
Media Characteristics
  • Throughput
  • Perhaps most significant factor in choosing a
    transmission medium is throughput
  • Cost
  • Cost of installation
  • Cost of new infrastructure versus reusing
    existing infrastructure
  • Cost of maintenance and support
  • Cost of a lower transmission rate affecting
    productivity
  • Cost of obsolescence

14
Media Characteristics
  • Size and scalability
  • Specifications determining size and scalability
  • Maximum nodes per segment
  • Maximum segment length
  • Maximum network length

15
Media Characteristics
  • Connectors
  • Connects wire to network device
  • Noise immunity

16
Types of Wired Media
  • Coax
  • Twisted Pair
  • Unshielded Twisted Pair (UTP)
  • Shielded Twisted Pair (STP)
  • Fiber Optics
  • Multimode Fiber (MMF)
  • Single-Mode Fiber (SMF)

17
Coax
Metal Shield
Conductor
Insulation
Cover
18
BNC T-Connector
Terminator
19
BNC Connector and NIC
20
NIC with BNC Connector
21
Coaxial Cable
22
Coax
  • Advantages
  • Throughput Very good transmission
    characteristics
  • Noise immunity High resistance of EMI/RFI
  • Size and Scalability Can support large networks
  • Cost Durable so is sometimes used in hostile
    environments
  • Disadvantages
  • Cost Can be difficult to work with and not used
    often so will need to be replaced if network
    changes
  • Connectors Less reliable and more difficult to
    use than the RJ-45 used with twisted pair

23
Twisted Pair
Interference in one wire balances interference in
the other. A perfectly balanced pair of wires
with perfectly symmetrical twists would be
totally immune to noise.
24
Damaged Twisted Pair
Imperfections reduce the cables resistance to
noise. Imperfections may be due to poor
manufacturing or poor installation practices.
25
Four-Pair UTP
26
RJ-45 Connector
27
NIC with RJ-45 Port
28
Categories of UTP
29
PreStandard UTP
30
Unshielded Twisted Pair (UTP)
  • Advantages
  • Cost Easy to work with and inexpensive,
    supported by most network standards so can be
    used for many years as network evolves
  • Connectors RJ-45 connector is extremely reliable
    when properly constructed
  • Size and scalability Individual cable segments
    must be short but structured cabling methods
    support very large networks
  • Disadvantages
  • Throughput Capable of lower bandwidths than coax
    or fiber
  • Noise immunity Have to be careful during
    installation to avoid noise

31
Shield Twisted Pair (STP)
  • STP is similar to UTP except it has a shielding
    similar to coax around the cable
  • Shielding must be grounded as with coax
  • Imperfections in shielding can increase noise in
    cable

32
STP
33
Shield Twisted Pair (STP)
  • Advantages
  • Cost More expensive and difficult to work with
    than UTP
  • Disadvantages
  • Throughput Similar to UTP
  • Noise Immunity Not significantly better in terms
    of noise resistance than UTP if not installed
    exactly right
  • Connectors Reliable but not as easy as RJ-45
    since shielding must be grounded
  • Size and scalability Not supported by as many
    standards as UTP

34
Fiber Optic Cable
35
Fiber Cable
Cladding
Core
Cladding and core are different types of glass
with different reflective indices. Light travels
down the core.
36
Fiber-Optic Cable
  • Single-mode fiber
  • Carries light pulses along single path
  • Multimode fiber
  • Many pulses of light generated by LED travel at
    different angles

Figure 4-29 Single-mode and multimode
fiber-optic cables
37
Fiber Connectors
ST Connector
SC Connector
Ends of cable must be polished smooth to
reduce light loss and fiber must be perfectly
aligned in connector.
38
Fiber NIC
ST Connector Port
Requires two fiber strands. One for send and
receive.
39
Multimode Fiber (MMF)
  • Light bounces off boundary between cladding and
    core
  • Causes light loss
  • Uses short wavelength LEDs and lasers
  • Short wavelength signals attenuate faster
  • Comes in 62.5/125 µm and 50/125 µm
  • More expensive cable than SMF but less expensive
    connectors and light sources

40
Single Mode Fiber (SMF)
  • Light is focused down center of core
  • Very little light lost
  • Uses expensive long wavelength lasers
  • Long wavelengths can travel very long distances
  • Comes in 8/125 µm
  • Cable is cheaper than MMF but connectors and
    light sources are very expensive
  • This makes SMF network equipment is very
    expensive

41
Graded MMF
  • Boundary between cladding and core is not abrupt
    so that light rays are bent toward the center
    rather than reflected
  • This causes less light loss

42
Fiber Optics
  • Advantages
  • Noise immunity Totally immune to noise, no
    electrical emissions so almost impossible to tap
  • Throughput Capable of very high bandwidths and
    distances
  • Size and scalability Capable of very long
    distances
  • Disadvantages
  • Connectors Fiber connectors require special
    training and care to make
  • Cost More expensive cable, more expensive to
    install and much more expensive equipment
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