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Transmission medium

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... pair of antenna can be aligned without interfering with another pair Microwave propagation is ... A signal traveling along ... Chapter 1 Introduction Author: – PowerPoint PPT presentation

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Title: Transmission medium


1
Transmission medium
  • We can say that transmission media belong to
    layer zero

2
Transmission medium
  • Transmission media can be divided into two broad
    categories
  • Guided media include twisted-pair cable, coaxial
    cable, and fiber-optic
  • Unguided media is usually air

3
Guided media
  • Guided media, which are those that provide a
    conduit from one device to another, include
    twisted-pair cable, coaxial cable, and
    fiber-optic cable.
  • A signal traveling along guided media is directed
    and contained by the physical limits of the
    medium
  • Twisted-pair and coaxial cable use metallic
    (copper) conductors that accept an transport
    signals in the form of electric current
  • Optical fiber is a glass cable that accepts and
    transports signals in the form of light

4
Twisted-Pair Cable
  • Consists of
  • two conductors (normally copper)
  • each with its own plastic insulation
  • twisted together

5
Twisted-Pair Cable
  • One of the wires is used to carry signals to the
    receiver
  • And the other is used as a ground reference
  • Receiver uses the difference between the two
    level
  • Interference (noise) and crosstalk may affect
    both wires and create unwanted signals
  • Receiver operates only on the difference between
    these unwanted signals
  • If the two wires are affected by noise or
    crosstalk equally
  • Receiver is immune (the difference is zero)
  • If the two wires are parallel
  • The effect of these unwanted signals is not the
    same in both wires (one close and one farther)
  • By twisting the pairs, a balance is maintained

6
Twisted-Pair Cable
  • The number of twists per unit of the length (e.g.
    inch) determines the quality of the cable
  • More twists mean better quality

7
Unshielded versus Shielded
  • Two common twisted-pair cable used in
    communications
  • Unshielded twisted-pair (UTP)
  • Shielded twisted-pair (STP)
  • STP has a metal foil or braided-mesh covering
  • Preventing the penetration of noise or crosstalk
  • It is bulkier and more expensive

8
Categories
  • EIA the Electronic Industries association
    classifies unshielded twisted-pair cable into
    seven categories which determined by quality (1
    lowest and 7 highest)

9
Connectors
  • Most common UTP connector is RJ45
  • R J stands for Registered Jack

10
Performance
  • One way measure performance is to compare
  • attenuation vs. frequency and distance.
  • A twisted-pair can pass a wide range of
    frequencies.
  • Figure 7.6 shows with increasing frequency,
    attenuation in decibels per kilometer (dB/km),
    sharply increase with frequency above 100 kHz.
  • Gauge is a measure of the thickness of the wire.

11
Application
  • Used in telephone Lines (UTP)
  • DSL lines (UTP)
  • Local area networks

12
Coaxial Cable
  • Carries signals of higher frequency ranges than
    twisted-pair cable
  • Coax has a central core conductor of solid or
    stranded wire (usually copper)
  • Encased in an outer conductor of metal foil,
    braid, or a combination of the two
  • The outer metallic wrapping services as
  • Shield against noise
  • Second conductor (completes the circuit)
  • Outer conductor is also enclosed in an insulating
    sheath
  • Whole cable is protected by a plastic cover

13
(No Transcript)
14
Coaxial Cable Standards
  • Coaxial cables are categorized by their radio
    government (RG) ratings
  • Each RG number denotes a unique set of physical
    specifications
  • Wire gauge of the inner conductor
  • Thickness and type of the inner insulator
  • Construction of the shield
  • Size and type of the outer casing
  • Each RG ratings is adapted for a specialized
    function

15
Coaxial Cable Connectors
  • Coaxial cable connector is BNC (Bayone-Neill-Conce
    lman)
  • Figure shows the BNC connector, the BNC T
    connector, and the BNC terminator

16
Performance
17
Applications
  • It was used in analog and digital telephone
    networks (replaced by fiber-optic)
  • Cable TV networks (replaced by fiber-optic)
  • Traditional Ethernet Lans

18
Fiber-Optic Cable
  • It is made of glass or plastic and transmits
    signals in the form of light
  • If a ray pf light traveling through one substance
    and enters another (more or less dense), the ray
    changes directions
  • Optical fibers use reflection to guide light
    through a channel

19
Fiber-Optic Cable
  • Glass or plastic core is surrounded by a cladding
    of less dense glass or plastic

20
Propagation Modes
  • Current technology supports two modes (multimode
    and single mode) for propagating light along
    optical channels
  • Multimode multiple beams from a light source
    move through the core in different paths
  • Multimode can be implemented in two forms
  • Step-index
  • Graded-index

21
Propagation Modes
22
Fiber Sizes
  • By the ratio of the diameter of their core to the
    diameter of their cladding micrometers

23
Cable compostion
24
Fiber-Optic Connections
  • Fiber-optic use three different type of
    connectors
  • Subscriber Channel (SC) connector
  • Used in cable TV and it uses a push/pull locking
    system
  • The Straight-Tip (ST) connector
  • Used for connecting cable to networking devices
  • MT-RJ in new connector with the same size as RJ45

25
Optical fiber performance
26
Fiber-Optic Connections
  • Applications
  • It used in backbone networks
  • For cable TV with coaxial cable (a hybrid
    network)

27
Advantages and Disadvantages of Optical
  • Advantages over twisted-pair and coaxial
  • Higher bandwidth
  • Less signal attenuation
  • Signal with fiber-optic can run for 50 km with
    requiring regeneration
  • 5 km for coaxial or twisted-pair cable
  • Immunity to electromagnetic interference
  • Electromagnetic noise cannot affect fiber-optic
    cables
  • Resistance to corrosive materials
  • Glass is more resistant to corrosive materials
    than copper
  • Light weight
  • More immune to tapping
  • Fiber-optic cables definitely more immune to
    tapping than copper cables

28
Advantages and Disadvantages of Optical
  • Disadvantages
  • Installation/maintenance
  • Because it is new technology, need expertise
  • Unidirectional
  • If we need bidirectional we need two fibers
  • Cost
  • The cables and interfaces are expensive

29
UNGUIDED MEDIA WIRELESS
  • Unguided media
  • transport electromagnetic waves without using a
    physical conductor (wireless communication)
  • Signal broadcast through air

30
UNGUIDED MEDIA WIRELESS
  • Unguided signals can travel from the source to
    destination in several ways
  • Ground propagation
  • Sky propagation
  • Line-of-sight propagation

31
UNGUIDED MEDIA WIRELESS
  • Ground propagation (below 2 MHz)
  • Radio waves travel through the lowest portion of
    atmosphere
  • Waves emanate in all directions from the
    transmitting antenna
  • Distance depends on the amount of power in the
    signal
  • Sky propagation (2 - 30 MHz)
  • Higher frequency radio waves radiate upward into
    ionosphere where they reflected back to earth
  • This type of transmission allows for greater
    distance with lower power output

32
UNGUIDED MEDIA WIRELESS
  • Line-of-sight propagation (above 30 MHz)
  • Very high-frequency signals are transmitted in
    straight lines directly from antenna to antenna
  • Antennas must be directional
  • Facing each other
  • Either tall enough or close enough

33
UNGUIDED MEDIA WIRELESS
  • Electromagnetic spectrum defined as radio waves
    and microwaves is divided into eight ranges,
    called bands

34
UNGUIDED MEDIA WIRELESS
  • Wireless transmission can be divided into
  • Radio waves
  • Microwaves
  • Infrared waves

35
UNGUIDED MEDIA WIRELESS
  • Radio waves
  • Radio waves waves range in frequencies between 3
    KHz and 1 GHz
  • Microwaves waves ranging in frequencies between
    1 and 300 GHz
  • Radio waves are omnidirectional (propagated in
    all directions)
  • The sending and receiving antennas do not have to
    be aligned
  • Disadvantage
  • One antenna interferences another antenna when
    they using same frequency
  • Radio waves that propagate in the sky mode, can
    travel long distance AM radio
  • Radio waves low and medium frequencies can
    penetrate walls inside a building
  • Advantage an AM radio can be received inside a
    building
  • Disadvantage we cannot isolate a communication
    to just inside or outside a building
  • Applications
  • Useful for multicasting Radio, television.
    Cordless phones and paging system

36
UNGUIDED MEDIA WIRELESS
  • Microwaves
  • Microwaves are unidirectional
  • Antenna need to be aligned
  • Advantage pair of antenna can be aligned without
    interfering with another pair
  • Microwave propagation is line-of-sight
  • For long distance communication
  • Very tall towers
  • Repeater
  • Very high-frequency microwaves cannot penetrate
    walls
  • Disadvantage if receiver inside a building

37
UNGUIDED MEDIA WIRELESS
  • Applications
  • Due to unidirectional properties, microwaves
    useful when unicasting (one-to-one) communication
  • Cellular phones
  • Satellite networks
  • Wireles LANs

38
UNGUIDED MEDIA WIRELESS
  • Infrared
  • From 300 GHz to 400 THz (wavelengths from 1 mm to
    770 nm)
  • Use for short-range communication
  • It has high frequency, cannot penetrate walls
  • Prevents interference between one system and
    another
  • Remote control not interfere with our neighbors
  • Can not be used outside because suns rays
    contain infrared waves (interference)
  • (IrDA) Infrared Data Association established
    standards for communicating between devices
  • Keyboards, mice, PCs and printers
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