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Agenda 1. QUIZ 2. HOMEWORK LAST CLASS 3. HOMEWORK NEXT CLASS 4. FREQUENCIES & PHYSICAL LAYER 5. NOISE 6. TRANSISSION LINES 7. FIBER 8. MICROWAVE 9. SATELLITES & EXAMPLES INTELSAT INMARSAT
Homework Chapter 7: 5, 6, 8, 11, 12, 16, 19, 23, 81, 85 Note: Since the substitute lecturer covered Juniper rather than the class viewgraphs, I’ll cover multiplexing (in syllabus as Session 4) and Error Detection (in syllabus as Session 5) next week.
Figure 7-4 Frequency Range for Twisted-Pair Cable Limitation is distance. Why?
Transmission Lines We understand transmission lines by oversimplifying them: a. Lump all resistances into a single large resistance. What is R? b. Lump all inductances into a single large inductance. What is L? c. Lump all capacitances into a single large capacitance. What is C? d. Lump all conductance (leakage) into a single large conductance. e. Assume perfectly uniform construction and perfect symmetry so it looks exactly the same from both ends. f. Lump all of the above into a simple impedance network and assume stability. What is Zo?
Transmission Lines Impedance mismatches (impedance of load does not equal impedance of the line) result in a standing wave ratio (how much energy is reflected back to the transmitter).
Figure 7-10 Shielded Twisted-Pair Cable Helps eliminate cross-talk. What is cross-talk?
EIA Categories of UTP • Category 1. The basic twisted-pair cabling used in telephone system. OK for voice & low speed data. • Category 2. Next higher grade. Generally good for voice & data up to 4 Mbps. • Category 3. Required to have at least 3 twists per foot and can be used for data transmission up to 10 Mbps. Standard for most telephone systems. • Category 4. At least 3 twists per foot & other conditioning to bring transmission rate up to 16 Mbps. • Category 5. Used for data transmission up to 100 Mbps.
Figure 7-11 Frequency Range of Coaxial Cable Why this lower limit?
Figure 7-12 Coaxial Cable RG 8, 9 & ll. Used in thick Ethernet RG 58. Used in thin Ethernet RG 59. Used for TV
Fiber Optics Attenuation: Light loss due to both scattering and absorption. Absorption: The amount of light loss due to its conversion to heat. Scattering: The disappearance of light due to its leaving the core of of a fiber. Chromatic dispersion: The tendency of a fiber to cause slightly differing wavelengths of emitted light to travel through the fiber at different speeds. (See Handout)
Fiber Optics--Markets Type Environment Type Fiber Common Problem Enterprise Building or campus Multi-mode Dirty patch cord Network Corroded Connector Cable New Installation Single-mode Certification of Contractor Multi-mode Installation Long haul Underground/sea Single-mode Breaks & splices Providers Conduit
Optical Power Budget 0 -5 -10 -15 -20 -25 -30 -35 Launch Power +2dB +2dB -3dB -3dB -2dB -4dB/k +1dB +1dB -3dB By this point you could be down to minus 20 dB By this point you could be down to minus 30 dB Launch Temp Coupling Aging Path Fiber Temp Coupling Repair, Srvce Power to Fiber Loss Loss Effect to Rx Safety Margin Source variables Connector & cable variables
Nominal Limits for Geosynchronous Orbit Daily Figure-8 Motion of Geosynchronous Satellite Mean circumference = 264,654 km Nominal Radius (from center of earth) 42,162 km Nominal Height (from surface of earth) 35,786 km Inclination Variation: (for ± 10 0, ± 7,352 km) Apogee-Perigee 85 km typical Active Satellite Box Typical Station-Keeping Volume = 1.62 x 1017 m3 N Latitudinal Motion (N/S) Orbit Motion Direction and Rotation Rate Match Earth’s E W Longitudinal Motion (E/W) Equatorial Plane S
Stationkeeping Window • Perturbations cause “Stationary” satellite to drift from • designated orbital slot • Causes varying roundtrip time (@ ± 285 ms) • Onboard propellant used to maintain position • Fixed and broadcast service satellites positioned to ± 0.050 75 km Earth 85 km 75 km 0.10 Satellite Drift NS EW Orbit Eccentricity 0.001 Equator ± 0.050 Nominal Geostationary satellite orbit
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