Forced SNR change on router no longer effective?!

Hi all,

A few weeks ago I noticed that my sync rate would no longer get over around 11300kbps despite nothing apparently changing at my end.
Over the last week or so, I've been backing off the forced SNR change on my router to see what happens following a hunch. Previously, I'd set it at around 55% of the MSAN set SNRM and it would sync at just over 12000kbps with the actual SNRM at about 3.7dB. At 54% now, it won't get over 11300kbps with a very, very similar SNRM. I've been backing it off 1% at a time and am now at 58% and it still hits the same/ very similar sync speeds with the same/ very similar SNRM figure.
MSAN target SNRM is displayed as 6.6dB and the router is a Billion BiPAC 7800N. My ISP is Vivaciti and I'm connected to Broadcom kit in the exchange.

The only change I've noticed in this period is that the upstream SNRM has gone from a inconsistent 10dB to a very consistent 6.5dB.

Has anyone else seen this? Or does anyone have any ideas?

Thanks,

Paul

more noise around perhaps ? The decline in SNRM on the upstream (presumably still at maximum speed) points to more noise, unless it's started doing power backoff (check upstream power).

Similarly lower speed for the same margin points to either more noise or more attenuation = less signal.

In reply to a post by yarwell:

The decline in SNRM on the upstream (presumably still at maximum speed) points to more noise

I would have thought quite the reverse. Less noise results in lower NM necessary to overcome it; more noise would require a larger NM to exceed the noise.

No. The more noise around the more it will eat in to the available margin.

No sure this is the same thing but for what it is worth for the last couple of weeks or so I have been unable to force change the SNR through my Netgear DG834GT. I have previously always forced it to around 1 from the default 6 and have found this to be quite stable. However now for some reason, on resyncing, the SNR seems to set to around 3.5 rather than 6 and I cannot force a lower figure. Accordingly I now have a profile of 4mbs instead of 4.5mbs. Frustrating!

Edited by deleted (Mon 24-Sep-12 23:53:12)

In reply to a post by b4dger:

No. The more noise around the more it will eat in to the available margin.

True and when it has gobbled up all or most of the available margin, it will negotiate a new higher margin sufficient to accommodate the known noise with some leeway (hence the word 'margin') with consequent lower Sync.

viz. High noise -> High Margin.

viz. High noise -> High Margin

Not really - high instability or variability of noise may lead DLM systems to raise target margin, or for an observed margin to be high if the noise has reduced since sync time.

With a rate adaptive system the noise margin should be close to target providing the speed is within it's limits - high noise on line = low SNR = low speed for same margin.

The margin is fixed, and the speed is variable. High margin only occurs with DLM or with speed hitting a cap.

Has anyone else seen this?

I'm getting something vaguely similar on my ADSL Max 20CN connection using the DGTeam firmware, no changes with the upstream data but using the same value of SNR % change I find I can't obtain a 4Meg sync rate anymore.

It's probably due to the exchange line management equipment getting it's own back on me for messing around with the connection

Then we were talking at cross-purposes.

I was referring to Target Margin set at sync time and you are talking about observed Margin varying over time. I agree with your point in that respect.

I was referring to the target margin - if it's 3 or 6 that's what it is, the target margin isn't a function of the noise excluding DLM systems.

If it gets noisier after sync then the observed margin will decline, if it gets better it'll increase.

But at sync time the target margin should prevail and result in whatever speed is required to achieve it. Hence the OPs speed decline for the same target margin suggests more noise (unless I misunderstood the OP).