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Chapter Four

Chapter Four. Transmission Basics and Networking Media. 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:

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Chapter Four

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  1. Chapter Four Transmission Basics and Networking Media

  2. 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

  3. 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

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

  5. Transmission Basics • Amplitude • Measure of a signal’s strength (height of the wave) • Frequency • Number of times a signal’s amplitude changes over a period of time • Expressed in hertz (Hz) (Heinrich Hertz) • Wavelength • Distances between corresponding points on a wave’s cycle • Inverse to frequency • Freq 1,000,000 cycles/second (1MHz) – WL 300m • Freq 2,000,000 cycles/second (2MHz) – WL 150m

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

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

  8. Transmission Basics • Binary system encodes using 1s and 0s • Bits(binary digit) can only have a value of either 1 or 0 • Eight bits together form a byte • Byte “01111001” = “121” on digital network • Noise or any interference that may degrade signals affects digital signals less than analog signals

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

  10. Transmission Basics • Digital more reliable than analog • Digital is less effected by noise • However, digital requires many pulses to transmit the same info an analog signal can transmit with a single wave • Higher reliability/efficiency make the extra digital signaling worth it

  11. Data Modulation • Modem • Name reflects function as modulator/demodulator • Digital to analog – analog to digital • 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 • Used by modern Ethernet networks

  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 • Commonly used to increase the amount of data that can be transmitted in a time period

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

  17. Transmission Direction • Statistical multiplexing • Similar to TDM • Assigns slots to nodes according to priority and need instead of in succession Figure 4-8: Statistical multiplexing

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

  19. 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

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

  21. 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

  22. Throughput Table 4-1: Throughput measures

  23. Baseband and Broadband • Baseband • Transmission form in which (typically) digital signals are sent through direct current (DC) pulses applied to the wire • DC requires exclusive use of wire’s capacity • Example: Ethernet networks • Broadband • Transmission form in which signals are modulated as radiofrequency (RF) analog pulses that use different frequency ranges

  24. 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

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

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

  27. 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

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

  29. Media Characteristics • Determining transmission media for your network: • Throughput • Perhaps most significant factor in choosing a transmission medium is throughput • Cost • Cost of installation – yourself vs. contractors • Cost of new infrastructure versus reusing existing infrastructure • Cost of maintenance and support • Cost of a lower transmission rate affecting productivity – wait times • Cost of obsolescence

  30. Media Characteristics • Size and scalability • Specifications determining size and scalability: • Maximum nodes per segment • Maximum segment length • Maximum network length • Latency is the delay between the transmission of a signal and its receipt

  31. Media Characteristics • Connectors • Connects wire to network device • Noise immunity • Thicker cables are generally less susceptible to noise • Installation location very important • Conduits can protect cabling from noise

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

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

  34. 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

  35. 10Base5 • Designation explanation: • 10 – throughput (10 Mbps) • Base – Baseband transmission • 5 – maximum segment length (500 meters)

  36. 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

  37. Thicknet Characteristics • In Thicknet networking, the transceiver is a separate device and may also be called a media access unit (MAU) Figure 4-16: Thicknet cable transceiver with detail of a vampire tap

  38. Thicknet Characteristics • Attachment Unit Interface (AUI) • Ethernet standard establishing physical specifications for connecting coaxial cables with transceivers and networked nodes • An AUI connector may also be called a DIX or DB-15 connector Figure 4-17: AUI connectors

  39. 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

  40. 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

  41. 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 • BNC barrel connectors are used to join two Thinnet cable segments together

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