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Chapter 9

Chapter 9. High-Speed Digital Access: DSL, Cable Modem, and SONET. 9.1 DSL Technology. ADSL Other DSL Technologies. ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses.

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Chapter 9

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  1. Chapter 9 High-SpeedDigital Access:DSL,Cable Modem, and SONET

  2. 9.1 DSL Technology ADSL Other DSL Technologies

  3. ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses. The existing local loops can handle bandwidths up to 1.1 MHz. ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop line.

  4. Figure 9.1DMT Upstream: 25 channels (6-30), one channel used for control, so 24 channels x 4000 Hz per channel x 15 bits/baud yields 1.44 Mbps. Theoretically. Downstream: 225 channels, one channel used for control, so 24 channels x 4000 Hz per channel x 15 bits/baud yields 13.4 Mbps. Likewise.

  5. Figure 9.2Bandwidth division

  6. Figure 9.3ADSL modem Filter often called a splitter

  7. Figure 9.4DSLAM

  8. 9.2 Cable Modem Traditional Cable Networks HFC Network Sharing CM and CMTS DOCSIS

  9. Figure 9.5Traditional cable TV network

  10. Note: Communication in the traditional cable TV network is unidirectional.

  11. Figure 9.6Second generation hybrid fiber-coaxial (HFC) network

  12. Note: Communication in an HFC cable TV network can be bidirectional.

  13. Figure 9.7Coaxial cable bands

  14. Downstream data are modulated using the 64-QAM modulation technique. The theoretical downstream data rate is 30 Mbps. Upstream data are modulated using the QPSK modulation technique. The theoretical upstream data rate is 12 Mbps.

  15. Figure 9.8Cable modem

  16. Figure 9.9CMTS

  17. 9.3 SONET SONET Devices SONET Frame Frame Transmission Synchronous Transport Signals STS-1 Virtual Tributaries Higher-Rate Service

  18. Note: SONET is a synchronous TDM system controlled by a master clock.

  19. Figure 9.10SONET STS Mux – multiplexes and demultiplexes SONET streams Regenerator – optical repeater but also changes SONET header information Add/drop multiplexer – can add and drop signals without changing entire mux stream

  20. Figure 9.11SONETFrame format

  21. Table 9.1 SONET rates

  22. Figure 9.12STS-1Data rate

  23. Figure 9.13Virtual Tributaries (VT) types A VT is a partial payload that can be inserted into a frame and combined with other partial payloads to fill out the frame. So instead of using all 87 payload columns of an SPE frame for data from one source, we can subdivide the SPE and call each component a VT. VT1.5 accommodates a T-1; VT2 accommodates the European CEPT-1 service at 2.048 Mbps, etc.

  24. Figure 9.14STS multiplexing Lower rate STSs can be multiplexed into higher-rate STS streams. Simple multiples are used to denote the stream (four STS-3s combine to create an STS-12).

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