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Network Media

Network Media. Chapter 4 Signal Transmission Network Media. Signal Transmission. Signaling—the way data is transmitted across the media Digital signaling Two discrete states 0 or 1, on or off Analog signaling Constantly changing electromagnetic waves. Digital Signaling.

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Network Media

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  1. Network Media Chapter 4 Signal Transmission Network Media

  2. Signal Transmission • Signaling—the way data is transmitted across the media • Digital signaling • Two discrete states • 0 or 1, on or off • Analog signaling • Constantly changing electromagnetic waves

  3. Digital Signaling • Two different voltages are used. One voltage to represent on and another voltage to represent off

  4. Analog Signaling • Constantly changing electromagnetic wave • Characteristics: • Amplitude • Strength of signal (height of wave) • Frequency • Amount of time needed to complete one cycle of the wave • Phase • Relative state of one wave in reference to another wave

  5. Attenuation/Noise • Loss of signal strength as signal travels across media • Signal must be amplified or regenerated to ensure that data is transmitted correctly • Noise on media can disrupt data signal • Static, cross-talk, etc. • Electromagnetic interference (EMI) • Radio frequency interference (RFI) • Amplifiers and regenerators are used to increase the distance that signals can travel

  6. Converting Analog to Digital • Modems • At sending computer, convert computer digital signal to analog signal for transmission via media • At receiving computer, convert analog signal to digital signal • Modulator/Demodulator

  7. Transmission Direction • Simplex—transmission of data in one direction only (television) • Half-duplex—transmission of data in both directions but only one direction at a time (CB radio) • Full-duplex—simultaneous sending and receiving of data (telephone)

  8. Multiplexers • Enables multiple signals to travel simultaneously by combining two or more separate signals and transmitting them together. • Multiplexer (mux) at sending end combines signals and demultiplexer (demux) at receiving end separates signals • Example: Cable TV--numerous signals travel through coaxial cable; circuitry in the TV, VCR, or cable box separate the signals into different channels

  9. Multiplexing Methods • Time Division Multiplexing • Divides channel into time slots--each device is allotted a time slot • Statistical Multiplexing • Number of time slots allotted for each device varies depending on priority and need • Wavelength Division Multiplexing • Used for fiber-optic (light); different wavelength used for each channel

  10. Throughput/Bandwidth • Throughput is the amount of data that can be sent across the network media in a given time. • Measured in bits per second • Bandwidth is the range of frequencies that the media can transmit • Frequently throughput and bandwidth are used interchangable • Two methods for allocating bandwidth: • Baseband • Broadband

  11. Baseband • Transmission signals use the entire media bandwidth. • Commonly used for digital signaling. • Most LANs use baseband signaling

  12. Broadband • Media bandwidth is divided into multiple channels. • Each channel can carry different analog signals • Broadband networks support multiple simultaneous signals over a single transmission medium

  13. Network Adapters (NICs or NACs) • Provide the physical connection between your computer and the network media • Transmit and receive data • Prepare data for the network cable • Send the data to another computer or device • Control the flow of data between the computer and the network media

  14. Media Characteristics • Throughput/bandwidth • Cost • Installation—cable cost, ease of installation • Maintenance—troubleshooting, repairing, replacing • Scalability • Node Capacity—max # of node, • Attenuation—max length of segment, max number of segments • Noise immunity • electromagnetic interference, radio frequency interference, and eavesdropping • Connectors

  15. Copper Coaxial cable Twisted-pair cable Glass Fiber-optic cable Wireless (Air) Radio waves Microwaves Infrared Network Media • Anything that carries the message through the network • Transmission media—Physical path through which computers send and receive signals

  16. Coaxial Cable (Coax) • Copper core surrounded by insulation and a sheath • Shielding makes it more resistant to interference • Two types of coax cable used in networks • Thinnet (10Base2)—RG 58 A/U • Thicknet (10Base5)—RG 62 Thinnet Thicknet

  17. Coaxial cable showing various layers Outer shield Insulation (PVC, Teflon) Conducting core Copper wire mesh or aluminum sleeve

  18. Thicknet cable transceiver with detail of a vampire tap piercing the core Thicknet Vampire tap Transceiver Drop Cable

  19. Coaxial Cable • Terminators used at both ends of network to prevent signal bounce back • Used with bus topology • BNC cable connector used for Thinnet cable; n-connectors are used for Thicknet BNC T-connector BNC cable connector BNC Terminator

  20. Coaxial Characteristics

  21. Twisted-Pair Cable • Similar to telephone wiring • Color-coded pairs of wire; twisted and encased in plastic coating • Unshielded twisted-pair and shielded twisted-pair cables UTP STP Shielding

  22. RJ-45 connector and jack

  23. Twisted Pair Cable Categories • Category 1-2: Voice communications and low speed data communications. • Category 3: Suitable for computer networks. Data transmission rates up to 10 Mbps. Currently used for phone installations (home) • Category 4: Data transmission rates up to 20 Mbps • Category 5: Data transmission rates up to 100 Mbps. Very popular for LANs. • Category 5E: Higher speeds are possible (200 Mbps); more twists • Category 6: Speeds up to six times faster than Cat 5 • Category 7: Speeds up to 1 Ghz (Gigabit)

  24. UTP Characteristics • Cost: Relatively inexpensive; depends on grade of copper and any enhancements • Installation: Easy to install • Bandwidth: 10-100 Mbps (Cat 5) • Higher speeds are possible (up to 1000Mbps—Cat5E, Cat 6 and Cat 7) • Node Capacity: Two (computer to hub) • Attenuation: 100 meters • EMI: Very susceptible to EMI and eavesdropping • Connector: RJ-45

  25. STP Characteristics • Cost: Relatively inexpensive (more UTP, less than Thicknet or fiber-optic. • Installation: Slightly more difficult than UTP • Bandwidth: same as UTP • Node Capacity: Two • Attenuation: 100 meters • EMI: Susceptible to EMI (but less susceptible than UTP) and eavesdropping • Connector: RJ-45

  26. Plenum Cable • A plenum is the space between the false ceiling and the floor above. • Plenum-grade cable is fire resistant and produces a minimum of smoke • More expensive than PVC cable and less flexible • May be required by fire code

  27. Fiber-optic cable • Contains one or more glass fibers (core) • Data transmitted via pulsing light • Two categories: Single-mode and multi-mode Optical fiber (core) Glass cladding Fiber-optic connectors: ST and SC Protective outer sheath (jacket)

  28. Fiber-optic Characteristics • Cost: More expensive than copper cable • Installation: More difficult than copper cable • Bandwidth: 100 Mbps to 1 Gbps • Node: 2 • Attenuation: Several kilometers • EMI: Not subject to EMI; immune to eavesdropping • Connectors: ST and SC are popular

  29. Cable Media Comparison

  30. Wireless Media (Atmospheric) • Infrared • Radio Frequency (RF) • Narrow-band • Spread-spectrum • Microwaves

  31. Wireless portable computer using an infrared light beam to print Infrared

  32. Infrared Transmission Systems • Use infrared light to transmit signals • Point-to-Point (Direct) or Broadcast (Indirect) • Point-to-Point (Direct)—highly focused and directed at a specific target • Line of Site • Broadcast—spread the signal to cover a wider area and allow reception of signal by several receivers • Signal can be bounced off walls and ceilings

  33. Infrared Characteristics • Line of site • Light must be able to reach target • Bandwidth: 100 Kbps to 16 Mbps • Tested at up to 100Mbps but slower speeds are currently standard • Attenuation: Depends upon the quality of light and atmospheric conditions • EMI: Can be affected by intense light. Point-to-Point transmissions are fairly immune to eavesdropping. However, broadcast transmission are more easily intercepted.

  34. Wireless portable computer connecting to a cabled network access point Network

  35. Radio Frequencies Characteristics

  36. Wireless bridge connecting two LANs

  37. Microwave Transmission • Terrestrial Microwave • Line of site (max distance ~ 23 miles) • Transmission can be affected by atmospheric conditions (rain/fog). Vulnerable to EMI, jamming and eavesdropping • Bandwidth 1-10 Mbps • Satellite Microwave • Can transmit data over vast distances • Extremely expensive if you put up your own satellite

  38. Example of Network Wiring patch cable

  39. Example Wiring Closet

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