P-661H/HW Series User’s Guide
Appendix B
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Appendix B
About ADSL
Introduction to DSL
DSL (Digital Subscriber Line) technology enhances the data capacity of the existing twisted-
pair wire that runs between the local telephone company switching offices and most homes
and offices. While the wire itself can handle higher frequencies, the telephone switching
equipment is designed to cut off signals above 4,000 Hz to filter noise off the voice line, but
now everybody is searching for ways to get more bandwidth to improve access to the Web -
hence DSL technologies.
There are actually seven types of DSL service, ranging in speeds from 16 Kbits/sec to 52
Mbits/sec. The services are either symmetrical (traffic flows at the same speed in both
directions), or asymmetrical (the downstream capacity is higher than the upstream capacity).
Asymmetrical services (ADSL) are suitable for Internet users because more information is
usually downloaded than uploaded. For example, a simple button click in a web browser can
start an extended download that includes graphics and text.
As data rates increase, the carrying distance decreases. That means that users who are beyond
a certain distance from the telephone company’s central office may not be able to obtain the
higher speeds.
A DSL connection is a point-to-point dedicated circuit, meaning that the link is always up and
there is no dialing required.
ADSL Overview
Asynchronous Digital Subscriber Line (ADSL) technology provides high-speed data access
across regular telephone or ISDN lines by making use of previously unused high-frequency
bandwidth. ADSL is asymmetric in the sense that it provides a higher downstream data rate
transfer (up to 8Mbps), than in the upstream transfer (up to 832 Kbps). Asymmetric operation
is ideal for typical home and small office use where files and information are downloaded
more frequently than uploaded.
Advantages of ADSL
1
ADSL provides a private (unlike cable telephone and modem services where the line is
shared), dedicated and secure channel of communications between you and your service
provider.
2
Because your line is dedicated (not shared), transmission speeds between you and the
device to which you connect at your service provider are not affected by other users. With
Summary of Contents for P-661H Series
Page 2: ......
Page 5: ...P 661H HW Series User s Guide Certifications 5...
Page 10: ...P 661H HW Series User s Guide 10 Customer Support...
Page 44: ...P 661H HW Series User s Guide 44 Chapter 1 Getting To Know Your ZyXEL Device...
Page 76: ...P 661H HW Series User s Guide 76 Chapter 3 Wizards...
Page 108: ...P 661H HW Series User s Guide 108 Chapter 5 LAN Setup...
Page 132: ...P 661H HW Series User s Guide 132 Chapter 6 Wireless LAN...
Page 192: ...P 661H HW Series User s Guide 192 Chapter 10 Trend Micro Security Services...
Page 196: ...P 661H HW Series User s Guide 196 Chapter 11 Content Filtering...
Page 202: ...P 661H HW Series User s Guide 202 Chapter 12 Introduction to IPSec...
Page 230: ...P 661H HW Series User s Guide 230 Chapter 13 VPN Screens...
Page 234: ...P 661H HW Series User s Guide 234 Chapter 14 Static Route...
Page 246: ...P 661H HW Series User s Guide 246 Chapter 15 Bandwidth Management...
Page 250: ...P 661H HW Series User s Guide 250 Chapter 16 Dynamic DNS Setup...
Page 280: ...P 661H HW Series User s Guide 280 Chapter 19 System...
Page 290: ...P 661H HW Series User s Guide 290 Chapter 21 Tools...
Page 296: ...P 661H HW Series User s Guide 296 Chapter 23 Troubleshooting...
Page 300: ...P 661H HW Series User s Guide 300 Appendix A...
Page 304: ...P 661H HW Series User s Guide 304 Appendix C...
Page 326: ...P 661H HW Series User s Guide 326 Appendix E...
Page 328: ...P 661H HW Series User s Guide 328 Appendix F...
Page 334: ...P 661H HW Series User s Guide 334 Appendix G...
Page 368: ...P 661H HW Series User s Guide 368 Appendix K...
Page 376: ...P 661H HW Series User s Guide 376 Figure 219 Java Sun...