ADSL FAQ

1. How does ADSL compare to cable modems?
2. What is the expected throughput?
3. What is the microfilter used for?
4. How do I know the ADSL line is up?
5. How does the P662 work on a noisy ADSL line?
6. Does the VC-based multiplexing perform better than the LLC-based multiplexing?
7. How do I know the details of my ADSL line statistics?
8. What are the possible reasons when the ADSL link is down?
9. What are the signaling pins of the ADSL connector?

1. How does ADSL compare to Cable modems ?

ADSL provides a dedicated service over a single telephone line; cable modems offer a dedicated service over a shared media. While cable modems have greater downstream bandwidth capabilities (up to 30 Mbps), that bandwidth is shared among all users on a line, and will therefore vary, perhaps dramatically, as more users in a neighborhood get online at the same time. Cable modem upstream traffic will in many cases be slower than ADSL, either because the particular cable modem is inherently slower, or because of rate reductions caused by contention for upstream bandwidth slots. The big difference between ADSL and cable modems, however, is the number of lines available to each. There are no more than 12 million homes passed today that can support two-way cable modem transmissions, and while the figure also grows steadily, it will not catch up with telephone lines for many years. Additionally, many of the older cable networks are not capable of offering a return channel; consequently, such networks will need significant upgrading before they can offer high bandwidth services.

2. What is the expected throughput?

In our test, we can get about 1.6Mbps data rate on 15Kft using the 26AWG loop. The short the loop, the better the throughput. Besides, please do not stay in menu 24.1 it will slow down the throughput.

3. What is the microfilter used for?

Generally, the voice band uses the lower frequency ranging from 0 to 4KHz, while ADSL data transmission uses the higher frequency. The microfilter acts as a low-pass filter for your telephone set to ensure that ADSL transmissions do not interfere with your voice transmissions. For the details about how to connect the microfilter please refer to the user's manual.

4. How do I know the ADSL line is up?

You can see the DSL LED on the P662's front panel is on when the ADSL physical layer is up.

5. How does the P662 work on a noisy ADSL?

Depending on the line quality, the P662 uses "Fall Back" and "Fall Forward" to automatically adjust the date rate.

6. Does the VC-based multiplexing perform better than the LLC-based multiplexing?

Though the LLC-based multiplexing can carry multiple protocols over a single VC, it requires extra header information to identify the protocol being carried on the virtual circuit (VC). The VC-based multiplexing needs a separate VC for carrying each protocol but it does not need the extra headers. Therefore, the VC-based multiplexing is more efficient.

7. How do I know the details of my ADSL line statistics?

You can use the following CI commands to check the ADSL line statistics.
`CI> wan adsl perfdata
CI> wan adsl status
CI> wan utopia disp
CI> sys log disp`
`CI> wan adsl linedata far
CI> wan adsl linedata near`

8.What are the possible reasons when the ADSL link is down?

The physical ADSL line may not be up if:
(1) The DSLAM is not Alcatel.
(2) If it is Alcatel, the firmware version should be above 3.1.

9.What are the signaling pins of the ADSL connector?

The signaling pins on the P662's ADSL connector are pin 3 and pin 4. The middle two pins for a RJ11 cable.

All contents copyright (c) 2002 ZyXEL Communications Corporation.