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Chapter 12 Long-Distance Digital Connection Technologies

Chapter 12 Long-Distance Digital Connection Technologies. Pulse Code Modulation DSU/CSU ISDN ADSL Cable Modem. To reproduce human voice up to 4 KHz, Nyquist sampling theorem implies that voice needs to be digitally sampled at 8 KHz ( once every 125 microseconds).

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Chapter 12 Long-Distance Digital Connection Technologies

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  1. Chapter 12 Long-Distance Digital Connection Technologies • Pulse Code Modulation • DSU/CSU • ISDN • ADSL • Cable Modem

  2. To reproduce human voice up to 4 KHz, Nyquist sampling theorem implies that voice needs to be digitally sampled at 8 KHz ( once every 125 microseconds).

  3. Pulse Code Modulation (PCM) • a standard for digital encoding of audio used in the telephone system. PCM takes 8bit samples at 8 Khz (note that bandwidth of digital voice channel is 64 Kbps)

  4. DSU/CSU • device which terminates the digital line • translates between the digital representation used by phone companies and the digital representation(eg. v.35, RS449, RS232) used by computer industry(figure 12.2)

  5. Digital Leased Lines • Cost depends on capacity (speed) and distance. • Fractional T1 digital circuit • 64kbps, 128kbps, 256kpbs • T1 line • 1.544 Mbps digital circuit capable of handling 24 digital voice circuits • Inverse multiplexing (bonding) (figure 12.4) • multiple T1 lines for higher bandwidth • T3 line(figure 12.3) • 45 Mbps digital circuit capable of handling 672 digitized voice circuits.

  6. Fiber Optic Digital Leased Lines • OC-1 circuit • 51.8 Mbps capable of handling 810 voice circuits • OC-3 circuit • 155 Mbps capable of handling 2430 voice circuits • Trunk • a high capacity circuit (eg. T1 trunk, OC-3 trunk) • OC-1 SONET frame contains 810 bytes(figure 12.6) • OC-3(figure 12.5) SONET frame contains 2430 bytes

  7. Integrated Services Digital Network (ISDN) • Basic Rate Interface(BRI): • 2B channels at 64kbps each and one D channel at 16kbps • Primary Rate Interface(PRI): • 24 64kbps channels

  8. Local Loop • wiring between subscriber’s residence and nearest Central Office (CO) •  aka “last mile”

  9. Asymmetric Digital Subscriber Line (ADSL)(figure 12.7) • a local loop technology that provides a higher bit rate downstream to the subscriber than upstream to the provider • can run simultaneously over the same wires as the standard phone service • is adaptive (overall speed is negotiated between each pair of ADSL modems) • uses both frequency division multiplexing(255 carrier frequencies spaced 4.1 KHz apart for downstream data transmission and 31 frequencies for upstream data transmission) and inverse multiplexing • overall downstream rate variable up to 6.4 Mbps while upstream rate up to 640 Kbps

  10. Cable Modem • uses existing cable tv wiring. • Uses broadband signaling (ie. Frequency division multiplexing) to send data. • Requires one cable modem at the CATV center • one cable modem for each subscriber whose modems use a common carrier frequency to encode data. • Each subscriber is assigned an address • Users must share overall bandwidth of 10Mbps with other subscribers whose modems use same carrier frequency

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