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Datornätverk A – lektion 7

Datornätverk A – lektion 7 . Kapitel 7: Transmissionsmedia Kapitel 8: Kretskoppling Bredbandsinfrastruktur Kapitel 9: Bredbandsaccesstekniker: DSL, Cable Modem. Chapter 7. Transmission Media. Figure 7.2 Classes of transmission media. Figure 7.3 Twisted-pair cable (TP).

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Datornätverk A – lektion 7

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  1. Datornätverk A – lektion 7 Kapitel 7: Transmissionsmedia Kapitel 8: Kretskoppling Bredbandsinfrastruktur Kapitel 9: Bredbandsaccesstekniker: DSL, Cable Modem.

  2. Chapter 7 TransmissionMedia

  3. Figure 7.2Classes of transmission media

  4. Figure 7.3Twisted-pair cable (TP)

  5. Figure 7.4UTP (Unshielded TP) and STP (Shielded TP)

  6. Table 7.1 Categories of unshielded twisted-pair cables

  7. Figure 7.5UTP connector

  8. Figure 7.7Coaxial cable

  9. Table 7.2 Categories of coaxial cables Ledningens karaktäristiska impedans är den impedans (eller resistans) ledningen skulle ha om den vore oändligt långt.

  10. Figure 7.8BNC connectors BNC-Bayonet Neill Concelman T-koppling

  11. Ledningsreflektioner • Se animering. • Ledningsreflektioner kan orsaka s.k. stående vågor, som innebär att vissa frekvenser släcks ut i vissa punkter på ledningen. • Reflektioner kan uppstå: • om ledningar med olika karaktäristisk impedans kopplas samman, • om en ledning får t.ex. en kläm- eller fuktskada, • om långa ledningar parallellkopplas (t.ex. om man stoppar in en ledning mellan T-kopplingen och datorn som är längre än halva våglängden), eller • om en ledning inte avslutas med en termineringsresistor som har samma resistans som ledningens karaktäristiska impedans.

  12. Ledningsreflektioner (Forts) • Viktigt vid bussnät baserade på koaxialkablar. • Vid bussnät är nätverkskortet högohmigt, dvs avbrott. I ledningens båda ändar behövs en terminering på samma impedans som ledningen karaktäristiska impedans, t.ex. 50 Ohm vid Ethernet koaxialkabel. • Vid TP-kablar innehåller Ethernetkortet en termineringsresistor, dvs det är lågohmigt. Därmed behövs ingen extra termineringsresistor. Men därför är det inte möjligt att ansluta flera datorer till samma TP-kabel, utan att det uppstår reflektioner. Datorerna måste anslutas till ett nätnav (hub) eller en växel (switch), och således bilda ett fysiskt eller logiskt stjärnnät.

  13. Kabeltyper för Ethernet • 10BASE5=Tjock Ethernet, 10Mbps, 500m avstånd, koaxial. • 10BASE2=Tunn Ethernet, 10Mbps, 200m, koaxial. • 10BASE-T, 10Mbps, 100m, TP=Tvinnad parkabel, hubnät. • 100BASE-T=Fast Ethernet, 100Mbps, 100m, TP, hubnät. • 1000BASE-T, 1000Mbps, TP, hubnät.

  14. Kontaktdon för Ethernet

  15. Figure 7.13Modes

  16. Figure 7.15Fiber-optic cable connectors

  17. Figure 7.16Optical fiber performance

  18. Figure 7.9Coaxial cable performance

  19. Figure 14.22Fast Ethernet implementations

  20. 100Base-FX • Fast Ethernet with fiber optic cables • Uses two optical fibers, one for transmission and one for reception

  21. Gigabit Ethernet • Provides speeds of 1000 Mbps (i.e., one billion bits per second capacity) for half-duplex and full-duplex operation. • Uses Ethernet frame format and MAC technology • CSMA/CD access method • Backward compatible with 10Base-T,100Base-T and 100BaseTX • Can be shared (hub) or switched

  22. Figure 14.29Physical layer in Gigabit Ethernet

  23. Gigabit Ethernet Implementations • Fiber • 1000 Base – SX • Short wavelengths, two fiber-optic cables • 1000 Base – LX • Long wavelengths, two fiber-optic cables • Copper • 1000 Base – CX • Uses shielded twisted pair copper jumpers • 1000 Base – TX • Uses category 5 twisted pair copper cable

  24. Figure 7.2Classes of transmission media

  25. Figure 7.17Electromagnetic spectrum for wireless communication

  26. Våglängd och frekvens Ju högre frekvens desto kortare våglängd.

  27. Vågutbredning av radio- och mikrovågor • Exempel: Radio-LAN använder ofta frekvensen 2.4GHz,dvs våglängden 300/2400 =0.125m. • Radioskugga kan uppstå bakom föremål med storlek några våglängder (några dm i vårt exempel). • Radiovågor dämpas kraftigt av metallnät, t.ex. armeringsjärn, med mindre hål än en halv våglängd (ca 6 cm i vårt fall). Metallnätet utgör då Faradays bur.

  28. Figure 7.19Wireless transmission waves 30kHz – 2GHz 2 – 300GHz Kort avståndeller line-of-sight 300 – 400GHz Line-of-sight • Fjärrstyrning • IRDA • Mikrovågslänkar (tvåparabolantenner på två huseller master) • Satellitkommunikation • Radio-LAN • Korthållskommukation(t.ex. Bluetooth) • Broadcasting (radiooch TV), • Mobiltelefoni

  29. Figure 7.20Omnidirectional antennas Används ofta vid radiovågor

  30. Note: Radio waves are used for broadcast communications, such as radio and television, and paging systems.

  31. Figure 7.21Unidirectional antennas Används ofta vid mikrovågslänkaroch satellitkommunikaton

  32. Note: Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.

  33. Chapter 8 Circuit SwitchingandTelephone Network

  34.            switch Telephone network – Local Switch • The telephone network uses switches • Every subscriber ( telephone jack in a house) has a twisted-pair wire connected to the closest telephone exchange. They are called local switches or local exchanges. subscriber • This cannot provide connection to subscribers connected to another local switch.

  35. Switches • What is a switch? • A central device usually used with a star topology • Can be built in hardware and/or software • Used to provide temporary connections between any two devices connected to the switch • A network of switches can be made if a very large number of devices spread in a large geographic space need to be connected

  36. Subscribers connected to the same swich   A Circuit Switch • Device with a number of inputs and outputs • Creates temporary physical connection between an input and output link • The local switch can connect each telephone with each other

  37. Figure 8.2A circuit switch

  38. Circuit Switching • Three phases of the connection: • Circuit establishment • Data transfer • Circuit disconnect • The bandwidth is guaranteed during the connection • The bandwidth cannot be used by anyone else, even if it is not needed at certain moment (no flexibility)

  39. Figure 8.4Crossbar switch

  40. Figure 8.5Multistage switch Space switching

  41. Figure 8.6Switching path

  42. Figure 8.7Time-division multiplexing, without and with a time-slot interchange

  43. Figure 8.8Time-slot interchange

  44. Figure 8.10TST switch (Time-Space-Time)

  45. Characteristics of the Switches • Space switches • The advantage is that if a cross point is available, the connection is almost instantaneous • The disadvantage is the need for many cross points which is expensive • Time switches • Advantage is that it does not need cross points • Limited by the maximum data rate of one line. • Introduces a fixed delay. • Combined switches combine the advantages of both types

  46. Figure 8.11A telephone system Accessnät (Spridningsnät)

  47. Hierarchy of the Telephone Network International network International gateway exchange National tandem exchanges regional tandem exchanges trunk network Tandem offices local tandem exchanges local network local exchanges (toll offices) subscriber lines (local loops)

  48. Chapter 9 Bredbandsaccess- tekniker

  49. Bredbands-infrastruktur Ethernet-LAN används ofta i flerfamiljshus

  50. 9.1 DSL Technology ADSL Other DSL Technologies

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