Actually, it turns out that DLM in FTTC is considerably more immune to suddenly dropping sync in this way.

It is much better to power-down the modem first, of course, as the DSLAM can detect the "dying gasp" bits in the final frames sent from the modem. However, we just don't get reports from frustrated users that they accidentally triggered DLM from any sort of disconnection.

If you'd been here a while, you'd know that we already know this.

_{Edit: The important bit, of course, is powering down the modem before removing the DSL cable. Powering it down only before plugging the cable back in is pointless.}

Edited by deleted (Sat 25-Jan-14 23:17:08)

As someone who, in the course of their work, will knowingly cause multiple disconnections on an FTTC or indeed ADSL circuit in a short space of time, I can say that what you suggest is poor advice.

I always power down on my ADSL2+ router before change the cable / faceplate myself. As the DLM haven't trigger downgrade but instead increase my sync rate with a nice speed.

Sorry to keep the post going I am wondering what a good SNR would be VDSL2

It is currently 4.5db or around that and it only manages to get as high 6.6 in the day and that only for about half an hour and them comes down again.

I been reading and apparently the higher the better?

But i'm not sure what a good SNR for a line of my length or whether it means I have a bit noise on my line?

When I had ADSL2+ with the aluminium cable I used to get a SNR as low as 0.1 - 0.0db sometimes which is extremely low that's when problems occured.

"The higher the better" has never been true except on ADSL Max when on a shortish line that easily sync'ed at 8128kbps.

In the past, on BTW circuits the nearer to 6dB the better. That changed a few months ago, as on a clean line the sync-time value can be set by the DLM to 3dB. So that becomes the reference point. Similarly, on unstable lines where the sync-time margin has been set higher to help achieve stability, the nearer to the reference point the better.

On FTTC/VDSL2 the noise margin in normal setups is nothing to do with the BTW DLM. It is to do with the Openreach one. The sync-time value used by that is 6dB, (though there are I believe ISP options that allow them to request a higher value). The nearer to 6dB the better. The greater the variance from that the stronger the indication is of unwanted interference somewhere.

SNR is not determined by line length. (That being the distance from the FTTC cabinet in the case of VDSL2). It is set so as to avoid disconnections being caused by electro-magnetic noise. My Noise margin page has a more detailed explanation, using ADSLx as the basis but the methodology is the same.

Edited by RobertoS (Sun 26-Jan-14 22:38:45)

Lol

Thank you for explanation, I like your website very informative . So I guess I shouldn't wrry to much about my SNR unless it way off 6db like in the low 3's and high 2's

I have checked tonight and it is even lower. Last night was 4.5db tonight into the 3db's.
Also my attainable rate is lower that what the modem is actually synced at.

Anyway the internet is still working well so I will only worry if it gets to the 2's or 1db's.