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Chapter Four

Chapter Four. Transmission Basics and Networking Media. Objectives. Explain data transmission concepts including full-duplexing, attenuation, and noise Describe the physical characteristics of coaxial cable, STP, UTP, and fiber-optic media

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Chapter Four

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  1. Chapter Four Transmission Basics and Networking Media

  2. Objectives • Explain data transmission concepts including full-duplexing, attenuation, and noise • Describe the physical characteristics of coaxial cable, STP, UTP, and fiber-optic media • Explain the benefits and limitations of different networking media • Identify the best practices for cabling buildings and work areas • Describe the methods of transmitting data through the atmosphere

  3. Transmission Basics • Transmission has two meanings: • Refers to process of issuing data signals on a medium • Refers to progress of data signals over a medium • On a data network, information can be transmitted via one of two methods: • Analog • Digital

  4. Transmission Basics • Both analog and digital signals are generated by electrical current, pressure of which is measured in volts • In analog signals, voltage varies continuously • In digital signals, voltage turns off and on repeatedly

  5. Transmission Basics Figure 4-1: Example of an analog signal

  6. Transmission Basics • Amplitude • Measure of a signal’s strength • Frequency • Number of times a signal’s amplitude changes over a period of time • Expressed in hertz (Hz) • Wavelength • Distances between corresponding points on a wave’s cycle

  7. Transmission Basics • Phase • Refers to progress of a wave over time in relationship to a fixed point Figure 4-2: Phase differences

  8. Transmission Basics Figure 4-3: A complex analog signal representing human speech

  9. Transmission Basics • Binary system encodes using 1s and 0s • Bits can only have a value of either 1 or 0 • Eight bits together form a byte • Noise or any interference that may degrade signals affects digital signals less than analog signals

  10. Transmission Basics Figure 4-4: Example of a digital signal

  11. Data Modulation • Modem • Name reflects function as modulator/demodulator • Modulation • Technique for formatting signals • Frequency modulation (FM) • Method of data modulation in which frequency of carrier signal is modified by application of a data signal • Amplitude modulation (AM) • Modulation technique in which amplitude of carrier signal is modified by application of a data signal

  12. Data Modulation Figure 4-5: A carrier wave modified by frequency modulation

  13. Transmission Direction • Simplex • Signals travel in only one direction • Half-duplex • Signals may travel in both directions over a medium but in only one direction at a time • Full-duplex • Signals are free to travel in both directions over a medium simultaneously • Also referred to just as duplex

  14. Transmission Direction • Channel • Distinct communication path between two or more nodes Figure 4-6: Simplex, half-duplex, and full-duplex transmission

  15. Transmission Direction • Multiplexing • Allows multiple signals to travel simultaneously over one medium • To accommodate multiple signals, single medium is logically separated into subchannels • For each type of multiplexing: • Multiplexer (mux) is required at sending end of channel • Demultiplexer (demux) separates the combined signals and regenerates them in original form

  16. Transmission Direction • Time division multiplexing (TDM) • Divides channel into multiple intervals of time Figure 4-7: Time division multiplexing

  17. Transmission Direction • Wavelength division multiplexing (WDM) • Used only with fiber-optic cable • Data is transmitted as pulses of light • Fiber-optic modem (FOM)is a demultiplexer used on fiber networks that employ WDM Figure 4-9: Wavelength division multiplexing

  18. Relationships Between Nodes • Point-to-point • Transmission involving one transmitter and one receiver • Broadcast • Transmission involving one transmitter and multiple receivers • Webcasting • Broadcast transmission used over the Web

  19. Relationships Between Nodes Figure 4-10: Point-to-point versus broadcast transmission

  20. Throughput and Bandwidth • Throughput is amount of data the medium can transmit during a given period of time • Also called capacity • Bandwidth measures difference between highest and lowest frequencies a media can transmit • Range of frequencies is directly related to throughput

  21. Transmission Flaws • 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

  22. Transmission Flaws Figure 4-11: An analog signal distorted by noise

  23. Transmission Flaws Figure 4-12: A digital signal distorted by noise

  24. Transmission Flaws • Attenuation • Loss of signal strength as transmission travels away from source • Analog signals pass through an amplifier, which increases not only voltage of a signal but also noise accumulated Figure 4-13: An analog signal distorted by noise, and then amplified

  25. Transmission Flaws • Regeneration • Process of retransmitting a digital signal • Repeater • Device used to regenerate a signal Figure 4-14: A digital signal distorted by noise, and then repeated

  26. Coaxial Cable • Consists of central copper core surrounded by an insulator, braiding, and outer cover called a sheath Figure 4-15: Coaxial cable

  27. Coaxial Cable Table 4-2: Some types of coaxial cable

  28. Thicknet (10Base5) • Also called thickwire Ethernet • Rigid coaxial cable used on original Ethernet networks • IEEE designates Thicknet as 10Base5 Ethernet • Almost never used on new networks but you may find it on older networks • Used to connect one data closet to another as part of network backbone

  29. Thicknet Characteristics • Throughput • According to IEEE 802.3, Thicknet transmits data at maximum rate of 10 Mbps • Cost • Less expensive than fiber-optic but more expensive than some other types of coaxial cable • Connector • Can include a few different types of connectors, which are very different from those used on modern networks

  30. Thicknet Characteristics • N-series connector (or n connector) • Screw-and-barrel arrangement securely connects coaxial cable segments and devices Figure 4-18: N-Series connector

  31. Thicknet Characteristics • Noise immunity • Because of its wide diameter and excellent shielding, has the highest resistance to noise of any commonly used types of network wiring • Size and scalability • Because of its high noise resistance, it allows data to travel longer than other types of cabling

  32. Thinnet (10Base2) • Also known as thin Ethernet • Characteristics: • Throughput • Can transmit at maximum rate of 10 Mbps • Cost • Less expensive than Thicknet and fiber-optic cable • More expensive than twisted-pair wiring • Connectors • Connects wire to network devices with BNC T-connectors • A seen in Figure 4-19, BNC barrel connectors are used to join two Thinnet cable segments together

  33. Thinnet (10Base2) • Characteristics (cont.): • Size and scalability • Allows a maximum of 185 m per network segment (see Figure 4-20) • Noise immunity • More resistant than twisted-pair wiring • Less resistant than twisted-pair wiring Figure 4-19: Thinnet BNC connectors

  34. Thinnet (10Base2) • Signal bounce • Caused by improper termination on a bus network • Travels endlessly between two ends of network • Prevents new signals from getting through Figure 4-20: A 10Base2 Ethernet network

  35. Twisted-Pair (TP) Cable • Color-coded pairs of insulated copper wires twisted around each other and encased in plastic coating • Twists in wire help reduce effects ofcrosstalk • Number of twists per meter or foot known as twist ratio • Alien Crosstalk • When signals from adjacent cables interfere with another cable’s transmission Figure 21: Twisted-pair cable

  36. Shielded Twisted-Pair (STP) • STP cable consists of twisted wire pairs that are individually insulated and surrounded by shielding made of metallic substance Figure 4-22: STP cable

  37. Unshielded Twisted-Pair • Consists of one or more insulated wire pairs encased in a plastic sheath • Does not contain additional shielding Figure 4-23: UTP cable

  38. Unshielded Twisted-Pair • To manage network cabling, it is necessary to be familiar with standards used on modern networks, particularly Category 3 (CAT3) and Category 5 (CAT5) Figure 4-24: A CAT5 UTP cable

  39. Comparing STP and UTP • Throughput • Both can transmit up to 100 Mbps • Cost • Typically, STP is more expensive • Connector • Both use RJ-45 connectors (see Figure 4-27) and data jacks • Noise immunity • STP is more noise-resistant • Size and scalability • Maximum segment length for both is 100 meters

  40. RJ-45 Connector Figure 4-27: An RJ-45 connector

  41. Fiber-Optic Cable • Contains one or several glass fibers at its core • Surrounding the fibers is a layer of glass called cladding Figure 4-28: A fiber-optic cable

  42. 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

  43. Fiber-Optic Cable • Throughput • Reliable in transmitting up to 1 gigabit per second • Cost • Most expensive type of cable

  44. Fiber-Optic Cable • Noise immunity • Unaffected by either EMI or RFI • Size and scalability • Network segments made from fiber can span 100 meters • Signals transmitted over fiber can experience optical loss

  45. Fiber-Optic Cable • Two popular connectors used with fiber-optic cable: • ST connectors • SC connectors Figure 4-30: ST and SC fiber connectors

  46. Atmospheric Transmission Media • Infrared transmission • Infrared networks use infrared light signals to transmit data through space • Direct infrared transmission depends on transmitter and receiver remaining within line of sight • In indirect infrared transmission, signals can bounce off of walls, ceilings, and any other objects in their path

  47. Atmospheric Transmission Media • RF transmission • Radio frequency (RF) transmission relies on signals broadcast over specific frequencies • Two most common RF technologies: • Narrowband • Spread spectrum

  48. Choosing the Right Transmission Media • Areas of high EMI or RFI • Corners and small spaces • Distance • Security • Existing infrastructure • Growth

  49. Chapter Summary • Information can be transmitted via analog or digital methodology • Throughput is the amount of data a medium can transmit during a given period of time • Noise is interference that distorts an analog or digital signal • Costs depend on many factors • There are three specifications that dictate size and scalability of networking media • Connectors connect wire to the network device

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