modems, modems, and more modems oct 24, 2002. announcements test #2 – oct 31 –it will cover...
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Modems, Modems, and more Modems
Oct 24, 2002
Announcements
• Test #2 – Oct 31– It will cover Chapters 8, 11, 12, 13, and 17
Class Objectives
• Modems-Past– Bell Family
• Modems-Present– ITU Recommendations– Cable Modem– ADSL
FIGURE 13-2 Acoustically coupled modem. (Reprinted with permission from Racal-Vadic.)
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-3 Common modem voice and data jacks. (Reprinted with permission from Racal-Vadic.)
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-4 Typical direct-connection installation. (Reprinted with permission from Racal-Vadic.)
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-5 Modulation techniques employed by modems.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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Transmission Modes
• Simplex– Data is sent in only one direction
• Half-Duplex– Data sent in both directions, but only one at a
time
• Full-Duplex– Data sent both directions simultaneously
FIGURE 13-6 Bell 103/113 frequency assignment. (Courtesy of Racal-Vadic.)
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-7 Bell 202 frequency assignment. (Courtesy of Racal-Vadic.)
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-9 Bell 212A frequency assignment for the high-speed mode. Frequency assignment for the low-speed mode is identical to the Bell 103 specification (See Figure 13-6).
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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M-ary
• Applies for PSK or Quadrature Amplitude Modulation (QAM)
• M = log2(n)
where M is the number of encoded bits
and n is the number of state changes
• See Example 13.1 in textbook
Phasor Diagram
• Based on geometry and the unit circle
• We use it to give us a visual representation of how the modulated signal behaves
• Used mainly to represent phase and amplitude relationship
• Commonly called a “Constellation” Diagram
Unit Circle
45
90
180
270
0
FIGURE 13-10 Phasor diagram for the Bell 212A modem.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-12 Phasor diagram for the Bell 208A modem.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-13 Phasor diagram for the Bell 209A modem depicting 9600-bps QAM.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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ITU Recommendations
• ITU sets standards for the international community.
• As a practical matter, most of the standards are compatible with the US Bell standards.
• Present modems can reconfigure themselves to be compatible with many V. recommendations through software options and upgrades.
See Table 15-1 of textbook
Internal PCI Modem Card
Features:•Internal Modem •PCI Slot required •56K v.90 Voice Capable
FIGURE 13-14 V.22bis 16-point signal constellation.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-15 V.32 trellis 32-point signal constellation.
Warren HiokiTelecommunications, Fourth Edition
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FIGURE 13-16 V.33 128-point signal constellation.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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ITU-TS V.90
• Is the basis of our “advertised” 56 kbps modems
• Has different data rate for transmit and receive– Transmits: 33.6 kbps– Receives: 40-53 kbps– Uses the characteristics of telephone company
infrastructure to optimize the receiver’s specs. – Look at example in textbook.
FIGURE 13-17 Comparison of a V.34 and V.90 modem connection: (a) V.34 connection showing analog-to-digital conversions in both directions; (b) V.90 connection to an ISP showing only one analog-to-digital conversion.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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Cable Modem
• Shares coax cable with television programming
• Uses “DOCSIS”: Data Over Cable Service Interface Specification
• Bandwidths are shared with other users– Downstream rates are the most affected by high
use– Effective if cable infrastructure is already in place
FIGURE 13-19 Cable modem setup in relation to CATV system.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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www.cable-modems.org
www.cable-modems.org
www.cable-modems.org
www.cable-modems.org
Asymmetric Digital Subscriber Line (ADSL)
• Uses the subscriber loop
• Uses equalizer-based design to improve bandwidth of subscriber loop cable
• Dedicated service– Data rates between Central Office and user
does not depend on the other users vs the Cable Modem
FIGURE 13-20 ADSL (digital subscriber line) modem connection.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-21 The ADSL modem uses frequency-division multiplexing (FDM) in the subscriber loop.
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-22 Analog loopback test setup. (Reprinted with permission from Racal-Vadic.)
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
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FIGURE 13-23 (a) Local DLB test setup; (b) remote DLB test setup. (Reprinted with permission from Racal-Vadic.)
Warren HiokiTelecommunications, Fourth Edition
Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458
All rights reserved.
Read the following
• 13.12
• 13.14-13.14.7
• 13.15-13.18