dslreports logo

    All FAQs Site FAQ DSL FAQ Cable Tech About DSL Distance DSL Hurdles »»


how-to block ads

2Wire modems have a number of indicators for DSL line quality. There are informational displays on the main user interface (http: //homeportal) under the Broadband Link tab: Details, but this same information and much more is available through the Management and Diagnostic Console (http: //homeportal/mdc/).

Using this 2Wire Homeportal 1000HG as an example, we can see the effects of being a long distance away from the Central Office and having a phone line that picks up some noise.

This is the Broadband Link - Statistics page of the MDC ( »homeportal/mdc/ )

The first thing to notice here in the Downstream section is the Current Rate is 1440 and the Max Rate is 1440. The ordered package is 768-1.5Meg and right now the line is synced at 1440. 100% of the available downstream space on the line is in use. The Current noise Margin at 8dB is very low and the Current Attenuation at 59dB is very high. All indicate this line is just about tapped out, in truth on good days this line will give a full 1.5Meg sync, but there is no way we could ever order the 3.0Meg package for it, it would never hold.
A better line would have a higher Noise Margin. 6dB is about as low as you can go. Numbers above 10dB are better, and above 16dB superb. Attenuation numbers above 60dB are poor, and above 64dB are just about unusable. Better lines would be in the 20-50dB range.

This page is the Troubleshooting - DSL Diagnostics display of the MDC - And is available on software versions 3.5.11 and higer-

Here we see another reason this line is not holding the maximum 1.5Meg sync. This line is seeing impulse nose and the 2Wire is calling it Suspicious. Here you might start looking around your installation for things that could be generating noise on your home line. Electrical dimmers, lights, wireless phones, motors, the computer itself or a printer, etc. near your phone line. If the noise source is in your home, you can correct it - try running a new phone line and using an NID splitter. Move the modem at least 3 feet away from anything that can produce electrical noise.
In this case the noise is outside the home as an new line and splitter were already installed, so there is little more that can be done inside.
Another line of this display is Uncancelled Echo - This would be reading suspicious if you had forgotten to put a filter on every phone, fax, tivo, cable box, alarm, etc. in the home. This reading would be high because an unfiltered device could cause more echo then the modem can compensate for and thus lead to lower sync rates. This does not always happen, but if you get a Suspicious reading for Uncancelled Echo, filters are the first thing to check!

The Training History shows the status of various readings each time the modem has to re-sync itself to the line. It gives the date and time and indications of the Sync rates and other readings. Using this information you can get an overall picture as to how well your line is performing over time and if problems are due to retrains or something else.

Looking at this history, you can see that for a few days we had a sync rate at the maximum for the package: 1536, and had some room to spare in the 1920-1984 range. The noise margins were low, in the 5dB to 7dB range and the Attenuation high. CRC are Cyclic Redundancy Checks on the data, and it is normal to have some errors, especially on a marginal line.
You can see a period of time between 3/21 and 3/28 where we held 1536 for 7 days, then we retrained every couple of days. It is not uncommon to go weeks or a month or 2 without a retain on good lines.

Here is the right side of the Training History, and the Impulse Noise Tones. The Exit Code gives you an indication of what caused the retrain. In most cases here it was Loss Of Signal Limit, but there are others.

If you have a higher speed package, and you are not getting the full sync, these displays may help give you an idea why and what to look for. If its Suspicious Echo, look at your Filters. If its Noise Tones, look for items that generate electrical noise near the phone line or move the phone line. If the noise is from outside your home there may be little you can do about it. If you see a steady decrease in sync rates over time, along with an increase in Attenuation and decrease in Noise Margin you may have a phone line that has bad splices or jumpers. If you also hear static on the line this would be a good indication and you should run an NID test by plugging you modem directly in at the NID test jack. If your numbers improve at the NID then your problem is in your house wiring and you need to track it down. If they do not improve the problem is in the outside phone line and you need to have it checked. Not all lines can support all speeds, so you have to see what the DSL provider can do. Installing a NID splitter and pulling a home run cat 5 cable is not a bad idea, but if your numbers are low to start with this may only be of marginal help - but can go a ways to help eliminate poor inside wiring and missed filters.


Feedback received on this FAQ entry:
  • None of the example pics show

    2012-01-08 04:35:10

  • great stuff to know. thank you

    2011-09-11 05:36:50

  • This was a very useful post. Thank you!

    2009-12-28 20:11:42

Expand got feedback?

by Riss_Centaur See Profile
last modified: 2005-04-05 00:44:15