C837 High value 'BER valid sec' (2nd post)

This is - in my experience - normal beheavior.

I have never seen a formal cisco explanation of sh dsl int atm0 output, but my interpretation is is that the bit error rate measurements were valid for that amount of time.

However, managing a lot of these c8xx routers, i also have lots of these were this timer stays at 0...

What is more important are the dB values and the "percentage used", together with the error counters. These give much better insights on the adsl line quality and stability.

Thanks for your answer,

I have about 150 827 and 837 routers and most of them have a value 0 for the "BER valid sec".

But it looks like on those where the value is high we got sometimes problems with the connection, the ATM line is dropped without any reason.

Very strange.

Did you find other sites with some explanation on the sh dsl int atm 0 output?

Kind Regards

Hi Tom, Joop!

I found this link that gives the field descriptions of the "sh dsl interface atm" output but doesnt go any further than that.

Regards,

Rob

A noise margin can never be too high, only too low.

This is the way i interpret these numbers:

Capacity used: lower = better (for the same speed) Noise margin: higher = better Attentuation: Lower = better

Hi Joop,

Are you sure about it never being too high?

When my ADSL was first installed about 3 years ago, my Noise Margin reading would bounce between 2db and 5db. Whenever it dropped below about 4db, I suffered from frequent retrains of the ATM connection (10

- 20+ per day!!!). I contacted my ISP and they agreed, the reading was a bit low, so they "tweaked" the DSLAM end and it eventually rose to between 7 - 11db and has hovered around those values ever since. As long as it was within those values the ATM link has been VERY stable for me, for months at a time...

About 9 months after the level change, I suffered some retrains again (about 3-4 per day), and when I checked I found that the Noise Margin was reading 14-15db. Anything over about 13db would eventually result in ATM retrains, anything less was stable for me. However this situation only lasted for a few days and then it returned to "normal" (about 8db).

A tech I know subsequently explained this to me that raising my Noise Margin meant my transmit level at the DSLAM was higher, which can adversely affected other ADSL services into the same DSLAM via Near End Cross-talk, due to the density of copper cable into the DSLAM premises. The reason for my issue when the reading was higher was because an adjacent user had had their line level increased too much, and that it was adversely affecting my line, so there seems to be some fine tuning required to establish "normal" use patterns for this reading. As explained to me, they only like increasing the users Noise Margin to just enough to provide stable service, without affecting adjacent users on the same DSLAM.

Cheers............pk.

Well, we are both correct here ;-)

As seen from the end user, the noise margin can never be too high. The higher it is, the better the signal-to-noise distance is and the smaller the chance is on errors and unstable beheavior, e.g. depending on external factors.

As seen from the adsl provider, there is an optimal signal level with a good compromise between crosstalk and error rate. He has to cope with the effects of more dsl signals in the wire bundles. So he does not like unnessecary high signal levels and he tweaks the signal levels so that they are 'just good enough'.