modems, modems, and more modems oct 24, 2002. announcements test #2 – oct 31 –it will cover...

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

All rights reserved.

FIGURE 13-3 Common modem voice and data jacks. (Reprinted with permission from Racal-Vadic.)




FIGURE 13-4 Typical direct-connection installation. (Reprinted with permission from Racal-Vadic.)




FIGURE 13-5 Modulation techniques employed by modems.




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.)




FIGURE 13-7 Bell 202 frequency assignment. (Courtesy of Racal-Vadic.)




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).




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.




FIGURE 13-12 Phasor diagram for the Bell 208A modem.




FIGURE 13-13 Phasor diagram for the Bell 209A modem depicting 9600-bps QAM.




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.




FIGURE 13-15 V.32 trellis 32-point signal constellation.




FIGURE 13-16 V.33 128-point signal constellation.




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.




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.




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.




FIGURE 13-21 The ADSL modem uses frequency-division multiplexing (FDM) in the subscriber loop.




FIGURE 13-22 Analog loopback test setup. (Reprinted with permission from Racal-Vadic.)




FIGURE 13-23 (a) Local DLB test setup; (b) remote DLB test setup. (Reprinted with permission from Racal-Vadic.)




Read the following

• 13.12

• 13.14-13.14.7

• 13.15-13.18

modems, modems, and more modems oct 24, 2002. announcements test #2 – oct 31 –it will cover...

Documents

new jersey

upper saddle river

warren hiokitelecommunications

us bell standards

frequency assignment

courtesy of racal

present modems

common modem voice