Target SNR is either 3db or 15db & changes every few minutes

mzrider · ‎29-11-2008

I have just replaced my DG834PN router with a DM111Pv1 & WNDR4500 system.
While monitoring the DM111P using Routerstats-Lite I can see that the target SNR goes between 3db and 15db maybe 10 to 20 times each hour. Each time the SNR is at 3db I get a sync speed of about 5900, & each time the SNR is at 15db I get a sync speed of about 2900.
After a lot of swapping I realise that this is not due to the modem because a DG834v4 and a DG834PN do the same thing. I did notice earlier this year that the target SNR had changed from 6db to 3db but I have never before noticed this "square wave" plot on my routerstats SNR graph.
Does anyone know the reason for this dual sync speed/SNR effect?

w23 · ‎08-01-2008

Sounds like DLM gone mad.
What exchange are you on?

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adamwalker · ‎27-04-2007

Does this get better or worse at any given time of day?
It could well be some form of interference affecting the line that's periodically altering the SNR.
If that is the case the line can be susceptible to interference at any point between yourself and the exchange, however it most commonly occurs in the home. With that in mind does any of your cabling between the router, phone etc and the master socket trail near to any power cables perhaps?
Adam

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Plusnet Help Team

mzrider · ‎29-11-2008

I am on the Ambergate exchange 01773 and the line length is 4.2km of copper, reported downstream attenuation = 57.5dB

Quote from: _Adam_Walker_
Does this get better or worse at any given time of day?

At peak evening times the "3dB" sync rate and the "15dB" sync rate are both a few 100kpbs lower than at 0630 in the morning but the very square graphs captured by Routerstats are the same shape and the two target dB values remain unchanged.
The wiring from the master socket to the only filter runs outside the house and does not run along side power cables.
What I did notice last night was that with only 1 PC connected to the router (so that I can control when the internet is in use was:-
1 - Power on PC, start Routerstats & wait a few minutes with nothing using the internet connection,
2 - Sync = approx 2900, SNR = 15dB
3 - Open a browser so that a few bytes are downloaded & instantly the line switches to sync = approx 5900, SNR = 3dB
4 - Close browser so internet is not used and a few minutes later the line switches back to sync = approx 2900, SNR = 15dB
Points 3 & 4 were 100% repeatable as tested about 6 times over a 1/2hour period.
This could be a very dumb question but is this a new bit of very very clever BT DLM trickery to ensure that the average crosstalk in any group of wires is lower because unused connections are being throttled back until they are used?
adie:green adjusted quote to remove full quote as per link:rules, but still leave some relevance ]

w23 · ‎08-01-2008

There's a new 'power saving' (Low Power Mode) thing being trialled 'green internet'? but I didn't think it was supposed to be on your exchange.
mentioned here http://community.plus.net/forum/index.php/topic,104899.msg894327.html#msg894327
Could be completely wrong but the behaviour kind of fits what you might expect.

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At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
Opinions expressed in forum posts are those of the poster, others may have different views.

GrahamC · ‎19-07-2009

Something akin to this...
http://www.zhone.com/support/manuals/docs/26/2600-A3-ZB20-70/adsl_power_management.htm

adamwalker · ‎27-04-2007

Quote
There's a new 'power saving' (Low Power Mode) thing being trialled 'green internet'?

It won't be that, AFAIK this is still in the early stages of trialling and should not cause faults with the service as you've just described.

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Adam Walker
Plusnet Help Team

w23 · ‎08-01-2008

I do agree Adam but the behaviour described is very non-typical for a fault condition.

Call me 'w23'
At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
Opinions expressed in forum posts are those of the poster, others may have different views.

MisterW · ‎30-07-2007

Quote
This could be a very dumb question but is this a new bit of very very clever BT DLM trickery to ensure that the average crosstalk in any group of wires is lower because unused connections are being throttled back until they are used?

I suspect its more likely to be RouterStats displaying the information incorrectly. Have you tried looking at the stats directly with another PC ?

Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.

GrahamC · ‎19-07-2009

If it is using some sort of power saving mode, it should be easy to spot.
Look for...
Link Power State: L0 = full power mode
Link Power State: L2 = power saving mode
...or somthing similar.
This should be observable from the router web GUI.

prichardson · ‎05-04-2007

Having done some checks, your line is presently operating in L2 (Low Power) mode, so what you are seeing is the expected symptoms.
What is not expected is that your line has L2 enabled on it at all.
Our suppliers have confirmed that there are instances when a customer will see L2 mode when they shouldn't. Looking at the data, your line appears to have fallen into one of these two categories.
Our suppliers are in the process of rolling this back and this is due to be complete today, but have noted that some lines may still see this until June 18th (unless DLM triggers a profile change).
DLM is designed to work with L2 mode correctly. For each data point it collects and uses for information processing, it will ignore those were the line has a L2 status (it retains the data though so we can see the line itself).
Capture.PNG (attached)
Shows and confirms it is in L2 mode at present
Untitled.png (attached)
Note the timeline at the bottom, the entry marked (*) on the 1st is when the problem for the you started and is infact one of the two known events that trigger it for customers that should not see it. The "Mgm Ds" result item clearly showing the SNR Margin spiking as is the design in L2 mode.

mzrider · ‎29-11-2008

Quote from: GrahamC
If it is using some sort of power saving mode, it should be easy to spot.
Look for...
Link Power State: L0 = full power mode
Link Power State: L2 = power saving mode
...or somthing similar.
This should be observable from the router web GUI.

Yes I can confirm Line Power State = L0 when at the high sync speed & Line Power State = L2 when at the low sync speed.

Quote from: P
Having done some checks, your line is presently operating in L2 (Low Power) mode, so what you are seeing is the expected symptoms.
What is not expected is that your line has L2 enabled on it at all.
Our suppliers have confirmed that there are instances when a customer will see L2 mode when they shouldn't. Looking at the data, your line appears to have fallen into one of these two categories.
Our suppliers are in the process of rolling this back and this is due to be complete today, but have noted that some lines may still see this until June 18th (unless DLM triggers a profile change).
DLM is designed to work with L2 mode correctly. For each data point it collects and uses for information processing, it will ignore those were the line has a L2 status (it retains the data though so we can see the line itself).
Capture.PNG (attached)
Shows and confirms it is in L2 mode at present
Untitled.png (attached)
Note the timeline at the bottom, the entry marked (*) on the 1st is when the problem for the you started and is infact one of the two known events that trigger it for customers that should not see it. The "Mgm Ds" result item clearly showing the SNR Margin spiking as is the design in L2 mode.

For what it's worth I do not have a problem with the L0/L2 power mode switching as long as it doesn't affect my IP profile and I get full speed when I need it. I only noticed it because I fitted a new modem. I don't know when this low power mode started but last year when the target SNR was 6db I got a sync of about 4700, now I'm getting 5700 to 5900. When you consider that when the Ambergate exchange was DSLmax enabled (in 2004?) for 1 or 2 years I only got a sync of about 1700 to 2700kbps, I think this is pretty good for a fairly long rural line.
Now I understand what is happening, no complaints here, just a happy customer 🙂

prichardson · ‎05-04-2007

As per my post, you should not expect any problems with the IP profile.
L2 only applies to ADSL2, i.e 21CN. So the profile is done by TR101, so at sync time. The sync event is when it first comes on, and is not re-triggered when a L2 event occurs (or subsequent return to L0).
The only time it may trigger again is when returning to L0 and the line determines that the current error rate on L0 requires a resync. However, this type of event would occur naturally in-life anyway without L2/0, for whatever reason a connection drops.

Nokk · ‎08-12-2009

Hi, I have had the exact same issues with my line operating in this L2 mode. Have a fault open and 2 engineer visits, but no one has considered that this was the cause of my fluctuating SNR.
Would someone at plusnet be able to take a look at my line to update the fault.

jojopillo · ‎16-06-2010

Hi Nokk,
The fault ticket has been with you since the 25th. As this is the case we would not update it unless you were to send it back to us. I'd suggest sending it back with any issues you're currently having and let the faults team pick it up.
Jojo

Target SNR is either 3db or 15db & changes every few minutes

Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes

Re: Target SNR is either 3db or 15db & changes every few minutes