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SNR margin constantly too low? BT Exchange not so clever or plusnet?

Kwak
Grafter
Posts: 84
Registered: 05-11-2007

SNR margin constantly too low? BT Exchange not so clever or plusnet?

Ever since yesterday I've had the ADSL connection dropping every few minutes.
Yesterday was wet and pretty windy, I don't know if it's blown some water in anywhere?

Phone line seems fine, no crackles when I pick it up..

I've disconnected phone so just ADSL + splitter, tried different splitter, still happening.

But what is annoying here is that all I've read is the other BT end of the line is apparently
supposed to change setting, I thought, if line keeps dropping, and I think it's the exchange side
that decides this? It's been doing this constantly now for more than 12 hours, probably 18.

I log onto the router, good draytek, and every single time the SNR margin is immediately just 2/3 DB
even 0 DB (Loop At 26db), fluctuating quickly down to 0, then it drops out again,
making the internet virtually unusable. Router log just keeps saying

PP Closed:  Remote Terminating (PPPoE) - is the remote side dropping me?

I don't want the maximum speed possible if it's cutting things too fine and if the connection is  going to drop, yet that seems to be exactly the decision the connection is making. It appears to be totally maxing out the connection speed with a too low SNR? From what I'd read I thought BT were supposed to target a safe 6db, not a risky 2 then drop 2 minutes later, over and over, for 18 hours!

e.g. this
    ADSL2+(G.992.5)    SHOWTIME    704000    16440833    2    26

Tiny 2 is the connnected SNR Margin.Then drops 2 minutes later.

I can't see how to change the SNR in my router unfortunately so I'm stuck really.

Is there nothing I can do other than raise a fault report?

 

Is there no way from this end I can request that the exchange gives me a little bit more stability even if it's a little bit slower?

9 REPLIES
Kwak
Grafter
Posts: 84
Registered: 05-11-2007

Re: SNR margin constantly too low? BT Exchange not so clever or plusnet?

I tried an old router and it was doing it as well, say 4 times in an hour, now back to primary router and doing it  less frequently (it was barely keeping up 2 minutes earlier). Been up 10 minutes.

Maybe one of those things but pretty strange to have a clean crackle free dial tone and very frequent ADSL disconnects?

And still don't undersand why, if SNR margin is a trade off with speed, it would be re-connecting at a very low SNR in a loop. (Unless it's nothing to do with SNR or wires and it's been a software thing down the line).

Kwak
Grafter
Posts: 84
Registered: 05-11-2007

Re: SNR margin constantly too low? BT Exchange not so clever or plusnet?

BTW are these stats normal?

ATM Statistics    TX Cells    RX Cells    TX CRC errs    RX CRC errs
                           11653       11287        0                  2530

That's almost 1/4 CRC errors on received cells if I understand that correctly?

Plusnet Staff
Plusnet Staff
Posts: 2,123
Thanks: 361
Fixes: 114
Registered: 22-08-2015

Re: SNR margin constantly too low? BT Exchange not so clever or plusnet?

Hi there @Kwak I am sorry to hear you're having problems with your broadband. I've looked into your account and from checking your connection, things aren't looking good:

 

 

I'd advise to run through the checks of the broadband troubleshooter at http://faults.plus.net including trying the test socket (if you have one). Explained here: https://community.plus.net/t5/Library/Testing-From-The-Master-Socket/ba-p/1322242

 

Failing this, the next step would be to the complete the troubleshooter to raise a fault to us as it's likely to require an engineer to investigate further. I apologise for the inconvenience caused.

I've joined the Plusnet Help Team as of May 2017. As such, I have a new forum account. Please direct any queries to @Gandalf. Thanks

 Anoush Mortazavi
 Plusnet Support
Kwak
Grafter
Posts: 84
Registered: 05-11-2007

Re: SNR margin constantly too low? BT Exchange not so clever or plusnet?

Well it's all strange. The router I believe logged reconnects very frequently all night, then a last one 7:45am then another about an hour later and it's been solid ever since at say 3DB margin.

ADSL2+(G.992.5)    SHOWTIME    1112000    18072909    3    25

Perhaps it was a red herring, and the exchange had a failing component or somethng, they've noticed and replaced?

Or taken the router with the dry solder joint off the washing machine?!

I had put the phone on speakphone and listened for crackles and wasn't hearing anything bad at all. Years ago when I had a similar issue I could hear something was wrong.

Kwak
Grafter
Posts: 84
Registered: 05-11-2007

Re: SNR margin constantly too low? BT Exchange not so clever or plusnet?

And the other stat on CRC errors:

    TX Cells    RX Cells    TX CRC errs    RX CRC errs
      881294    6097950    0    1746

Which seems far more reasonable!

Thomas5020
Grafter
Posts: 25
Thanks: 2
Fixes: 1
Registered: 29-06-2016

Re: SNR margin constantly too low? BT Exchange not so clever or plusnet?

My SNR margin has been slowly getting worse throughout the past couple of days and now my connection is just like yours. I give up. Virgin mobile 4G obliterates my landline. 

Superuser
Superuser
Posts: 10,023
Thanks: 1,562
Fixes: 19
Registered: 22-08-2007

Re: SNR margin constantly too low? BT Exchange not so clever or plusnet?

@Thomas5020 - please start your own thread so that help specific to your issue might be offered.

@Kwak - exactly which Draytech router is this?  Have you altered any settings therein to lower the SNRM?

Both of these reports have the hall mark of either a degrading phone line or local interference.

Can each of you (on your own threads) please look at the speed issues thread (link below) and get the FULL router stats posted to your threads.  Just speeds and error counts are not over useful - also need to see other line metrics as well - attenuation and SNRM figures.

Also perform the BTw speed test - further diagnostics and post the results.  In the meantime...

Please perform a quiet line test - dial 17070 select option 2 using a corded phone plugged into the test socket behind the face plate of the master socket. It should be silent. A noisy phone line (or no dial tone) will have a marked adverse impact on the performance of broadband.

If the line is noisy or there is no dial tone, then a PHONE LINE fault needs to be raised with your phone provider. If this is PlusNet, you can report a fault on line using the button below.

Kwak
Grafter
Posts: 84
Registered: 05-11-2007

Re: SNR margin constantly too low? BT Exchange not so clever or plusnet?

My problem has gone away, solid 81 hours connection time. I didn't change the router SNR margin settings. I found conflicting info as to whether I could, I think if I reflashed the firmware I could have, but I've learned from bitter experience that often if it's not broken don't fix it, it's been stable up until last week. I telneted into the router and the command didn't exist.

I'm pretty sure it must have been something at the exchange or further down the line, since friday morning at around 8-9 am problem of reconnecting every few minutes just went away. Never a single crackle on the line.

The wierd thing I found, as I say, was I thought if the line quality was iffy it would up the allowed margin, but that didn't seem to happen. But maybe it was some related piece of hardware somewhere failing and nothing to do with line quality. Who knows.

Superuser
Superuser
Posts: 10,023
Thanks: 1,562
Fixes: 19
Registered: 22-08-2007

Re: SNR margin constantly too low? BT Exchange not so clever or plusnet?

It can all be a bit of a variable feast.  When the line synchs up, it does so at the TARGET SNRM.  There after the REPORTED SNRM is relative to the back ground noise on a line .... which in the absence of anything faulty will vary, especially after dusk.  Therefore when a line last synced and when you look at the SNRM figure is important to interpretations.

A normal line will synch with a target of 6dB.  Night time radio interference can depress the SNRM by up to 2-3dB.  If the line synch was during the day you might see 3-4dB reported after dusk; if during the hours of darkness, you might see 8-9dB during the day.

The router and exchange will try hard to keep a line connected, moving the TARGET up as necessary, however if there are issues on the line, at any time you look, you might find that the REPORTED SNRM is still low.

An intermittent bad line joint - which can 'repair' its self by the weather improving or an incoming call - can cause problems similar to those reported.  If you have not done so already I would recommend following the full fault reporting procedure to enable a proper line check to be performed ... less your line fails completely.