Billion UK Forum

I set the margin at 6. At night the margin dropped to about 4, and the following day it recovered a little - not to 6 but to about 4.5. Then the next night the margin dropped to about 2.5 then recovered the following day to about 3. this has been going on for days and I am now at about 1.5 during the day and at night it drops below 1. Right now (9pm) it is at 1.1.

Throughout this period there have been no disconnects and everything is fine, but if it goes on like this then I suppose it will disconnect.

Does anyone know if there is a reason why the margin has never recovered to the target of 6 which i set in the hidden menu?

thanks

Because that's a percentage if I'm not mistaken. There for 6 is 6% and that's 6% of the sync SNR meaning VERY LOW.

Example would be if your Sync SNR was 8 the target would be 0.48 SNR at 6%

the table below should help you.

• Your current SNR target margin, Your desired SNR target margin, The number you should enter
  6 dB 4.5 dB 75
  6 dB 3 dB 50
  9 dB 6 dB 50
  9 dB 4.5 dB 25
  9 dB 3.5 dB 1
  12 dB 9 dB 50
  12 dB 6.5 dB 1
  12 dB 6 dB 65550
  12 dB 4.5 dB 65525
  12 dB 3 dB 65500
  15 dB 12 dB 50
  15 dB 9 dB 65550
  15 dB 6 dB 65500
  15 dB 4.5 dB 65475
  15 dB 3 dB 65450
  18 dB 15 dB 50
  18 dB 12 dB 65550
  18 dB 9 dB 65500
  18 dB 6 dB 65450
  18 dB 4.5 dB 65425
  18 dB 3 dB 65400

Table was taken from another post on another forum. The later values look crazy but hopefully your SNR is before the insane ones

Hi

This sounds completely normal.

Bit swapping takes place where frequencies that become unusable due to more noise, especially during the night, have their capacity swapped to better frequencies, these are usually lower ones. As the lower frequencies are now having to carrying more data, they have less signal to noise ratio so your SNR drops.

The problem is that once all the bits are swapped from a frequency, that frequency (bin) is turned off. When the day arrives and that frequency is probably usable again, ADSL has no mechanism for turning on that frequency again and relieving the load on other frequencies and so recovering the original signal to noise ratio.

In order to reuse those frequencies you need to drop the line and re-sync. It is only during a re-sync that all the frequencies are rescanned for usability again. This is just how ADSL has been designed.

So over the course of time, more and more frequencies get switched off but not turned back on again, and at some point the signal to noise ratio may become so bad that the line will spontaneously drop and re-sync, and so the cycle continues.

Most people are lucky with ADSL in that after a few cycles of bad noise over the course of a couple of days, like natural selection all the frequencies left are stable and the line remains up quite happily for a long period all be it with a reduced SNR.

Essentially the SNR margin is the initial buffer to cater for frequencies having to be turned off, so if your SNR reduces but all is stable, it has done it's job.

Of course there are all sorts of random events that will gradually knock out other frequencies over time, so eventually your line will drop and re-sync, however that is exactly how ADSL is designed to work, it isn't meant to guaranteed a 100% constantly connected connection, it is designed to extract as much speed as possible out of the old telephone line and to do that we have to accept it isn't 100% reliable.

Regards

Phil

I know this thread is a few months old now but what phil says about tones that become unusable at night are not re used the next day is true for many routers like the Netgear dg834gt, but in my experience this is not true for all routers.
The 2wire 2700hgv does reuse tones the next day that become unusable at night before !

As i have just bought the 7800n i hope these tones are re allocated, or else it looks like it may be short lived, i hope not !

Paul.

maximod wrote:I know this thread is a few months old now but what phil says about tones that become unusable at night are not re used the next day is true for many routers like the Netgear dg834gt, but in my experience this is not true for all routers.
The 2wire 2700hgv does reuse tones the next day that become unusable at night before !

As i have just bought the 7800n i hope these tones are re allocated, or else it looks like it may be short lived, i hope not !

Paul.

They do recover from overnight lows but not necessarily back up to the Target SNRM - could depend on time of day and which day etc.

I found with my 7800N when I first got it that wiring up would double the SNRM from a low, which was useful late at night when it was sometimes dropping to 0.4dBM.

Sometimes it would hang on at that low and sometimes It would dc and I would know when it had hit the floor because of the lag it used to produce - but it doesn't increase by that much now when I wire up.

Something you could check out with your 7800N if you normally run wireless and notice that it's getting a bit low.

The lowest it drops these days from a 6dBm profile is down to ~2.6 but when it used to drop really low, I'd just switch it off overnight and everything would be fine the next morning.

Hi

maximod wrote:I know this thread is a few months old now but what phil says about tones that become unusable at night are not re used the next day is true for many routers like the Netgear dg834gt, but in my experience this is not true for all routers.
The 2wire 2700hgv does reuse tones the next day that become unusable at night before !

As i have just bought the 7800n i hope these tones are re allocated, or else it looks like it may be short lived, i hope not !

Paul.

I doubt that very much as the ADSL specification doesn't allow for that. Even with seamless rate adaptation, tones lost and turned off are never reused. You only get them back with a drop and re-sync.

Yes the SNR can certainly recover up to the same level if bit-swapping hasn't resulted in tones being turned off but just having a reduced data capacity, these tones will get bit-swapped back to carry their original capacity during quieter noise periods and SNR recovers to the same level.

If you can run something like DMT on a modem you can visually see the tones being turned off, and they never come back without a full resync.

Regards

Phil

Hi Phil,
Well looking at the 7800n today, the overnight tones that became unusable have not re emerged today, so in effect the daytime snrm has not fully recovered from yesterday daytime.
This will cause a gradual decline over time as the dg834gt did.

The 2700hgv did recover tones that got unusable at night, so looks to be quite intellient in this department !

I know rate adaptive is a different animal as the router can dynamically resync amongst other things.,

I will put my old 2700hgv back on over the next couple of days and take a screen shot of day sync/night/ and next day to compare.

Paul.

Hi

maximod wrote:Hi Phil,
The 2700hgv did recover tones that got unusable at night, so looks to be quite intellient in this department !

Is the 2700hgv bit-swapping? Perhaps it isn't actually bit swapping so tones are not being turned off. You can disable bit-swapping on the 7800 but this usually results in an unstable line.

Some modems have been known to drop and resync but not report that fact, maybe it is just re-syncing but outwardly showing no signs of it giving a false appearance of being better?

Regards

Phil

Hi Phil,
Yes the 2700hgv is bitswapping, but i am suffering the known dns issue where the 2700hgv fails to load certain url's.
Just tried to downgrade from v5 to v4.5 and bricked it, typical as this one (of several i have) gave the highest sync

As i have several others i will test bitloading on one of them between day/night/day.

Regarding the 7800n, it is a pity that changing certain parameters like user/pass authentication causes complete reboot of router, so causing re sync, the 2700hgv does not do so.

Paul.

I have now just taken 3 screen grabs of the 2700 router taken yesterday afternoon, then early hours, then today at 1pm.
You can clearly see bitloading re appear the next day.
There has been no resync between the 3 readings.