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Router, Line or the will of BT?

Plusnet Alumni (retired) orbrey
Plusnet Alumni (retired)
Posts: 10,540
Registered: 18-07-2007

Re: Router, Line or the will of BT?

Hi GrahamC,
I can see the interleaving ticket has now been picked up Smiley Hope everything stays working for you.
GrahamC
Grafter
Posts: 257
Registered: 19-07-2009

Re: Router, Line or the will of BT?

Thanks Matt
me too  Roll eyes
I'm still monitoring the connection, been up since Friday afternoon, no errors reported, and no fluctuations in SNRM. I'm suprised there's been no movement on the BT profile yet though.
cheers
Graham
Plusnet Alumni (retired) orbrey
Plusnet Alumni (retired)
Posts: 10,540
Registered: 18-07-2007

Re: Router, Line or the will of BT?

Well if nothing's changed when the interleaving order has completed and the line's still stable then we'll get an SNR reset sorted in order to let the line retrain, if you're happy with that?
GrahamC
Grafter
Posts: 257
Registered: 19-07-2009

Re: Router, Line or the will of BT?

Well, just doing another speed test as you were posting...
The BT profile just increased to 6 Mbps (from 5.5 Mbps) although with a sync rate of 7232 I think 6.5 Mbps would have been nearer the mark, but hey, it's going in the right direction  Smiley
How will I know the interleave order is complete, will the DSL drop/reconnect?
Community Veteran
Posts: 19,100
Thanks: 437
Fixes: 21
Registered: 31-08-2007

Re: Router, Line or the will of BT?

You need 7296 for 6.5M, frustrating. You'll probably get it when interleaving is off if you resync in daylight.
Edit: Brain must have been turned off, should have said 7392.
GrahamC
Grafter
Posts: 257
Registered: 19-07-2009

Re: Router, Line or the will of BT?

Curiosity got the better of me, and last night I rebooted the router to check if the interleaving had been removed.
Interleaving had been removed and the sync went up very slightly (7232 to 7264), but I noticed erratic SNRM figures in the stats, so started logging again with routerstats. See graph 1.
The SNRM was fluctuating between 12db and 15db with the connection forever trying to bitswap. After a couple of hours, it was obvious this situation was not going to settle, so I rebooted the router again, this time with a drop in sync from 7264 to 7008, but still the fluctuations in SNRM continued. After a further 30 minutes or so, I decided to switch off the router overnight.
In use, the connection didn't drop and seemed OK apart from the tech stuff going on in the background. It was though each end of the connection was trying to outdo the other.
Turned the router back on this morning with the following results:

Mode:                                      ADSL_G.dmt
Traffic Type:                              ATM
Status:                                    Up
Link Power State:                          L0
 
                                          Downstream Upstream
Line Coding(Trellis):                      On         On
SNR Margin (0.1 dB):                       151        220
Attenuation (0.1 dB):                      125        105
Output Power (0.1 dBm):                    198        121
Attainable Rate (Kbps):                    7008       1016
Rate (Kbps):                               6976       448
K (number of bytes in DMT frame):          219        15
R (number of check bytes in RS code word): 0          0
S (RS code word size in DMT frame):        0.50       1.00
D (interleaver depth):                     1          1
Delay (msec):                              0.13       0.25
INP (DMT symbol):                          0.00       0.00
Super Frames:                              0          0
Super Frame Errors:                        0          0
RS Words:                                  0          0
RS Correctable Errors:                     0          0
RS Uncorrectable Errors:                   0          0
HEC Errors:                                0          0
OCD Errors:                                0          0
LCD Errors:                                0          0
Total Cells:                               166903111  0
Data Cells:                                503134     0
Bit Errors:                                0          0
Total ES:                                  0          0
Total SES:                                 0          0
Total UAS:                                 11         11

Sync rate slightly lower again, but the SNRM is now stable at 15db. Uptime 3 hours with no errors. See graph 2
I don't want to reset again, as I've just had my first BT Profile increase in months, but I'm still synching below 7000.
jojopillo
Grafter
Posts: 9,786
Registered: 16-06-2010

Re: Router, Line or the will of BT?

Hi GrahamC,
I imagine the drops in the graph were you. As Matt suggested I could retrain the line at 6dB SNR if you like. That would bring your sync rate up.
Jojo Smiley
Community Veteran
Posts: 19,100
Thanks: 437
Fixes: 21
Registered: 31-08-2007

Re: Router, Line or the will of BT?

Hi Graham,
I wouldn't suggest any retraining of the line under current conditions, you will end up with a lower Fault Threshold Rate.
A couple of things - generally, to up the sync speed, it is better to resync in Daylight hours (typically an hour after sunrise to an hour before sunset to get the optimum). This is because atmospheric propagation at frequencies that can interfere with broadband increase after dark, it can increase at other times due to certain atmospheric weather patterns but this is less common. Also after dark there are more electrical appliances on, some of which will create noise at broadband frequencies.
Last night, just after midnight something happened producing a lot of noise that continued through the night - in a way it's a shame you didn't leave it all running so we could see if and when it stopped. In my view this is clearly some electrical source that switched on at that time. The noise didn't change throughout that period - if you turn on the average noise plotting in Routerstats as well, that would have probably been a flat line showing that it wasn't due to propagation. Re-syncing when you have noise like that generally results in lower sync speeds.
What's bugging me a bit, is the fact that you seem to be fairly close to the exchange (according to the router figures) and I'm surprised that you aren't syncing at higher speeds. This suggests a continuous high level of background noise which needs to be tracked down.
My suggestion would be to leave the modem/router running continuously for the time being, then we will know if there are any drops in sync, and leave Routerstats running (turn on that average noise plot as well) to see what interference appears and when.
Once we've more info, it may be possible to track down the source.
GrahamC
Grafter
Posts: 257
Registered: 19-07-2009

Re: Router, Line or the will of BT?

OK, before I go any further with this, the observations I made this morning during the resets/reboots were as below, keeping in mind I've monitored the connection for 3 days solid and no SNR interference was recorded.
1. After the reboot, via options in the router interface, there was significant bitswapping going on. Over the 2 hours this ran into hundreds of bits, caused no doubt by the fact the SNRM was fluctuating. Another reboot using the same method produced similar results.
2. Turning off the router, and leaving off for a number of hours enabled a connection straight away, with no bitswaps.
This raises a couple of questions:
In 1 above, are the router and DSLAM trying to outdo each other, continually trying to modify both the SNR and bitswapping?
In 2 above, leaving the DSLAM and router to their own devices for several hours enabled a connection with no further SNR fluctuations/biswapping, i.e. either the DSLAM and/or router had reset sufficiently.
In an attempt to understand this I've just done a futher 2 reboots:
a) In router options Bitswap enabled, gave an immediate SNRM fluctuation between 12 and 15 db, with a drop in sync. 6976 - 6816
b) In router options Bitswap disabled, gace a steady SNRM with the sync going back to it's previous speed. 6816 - 6976
Should this Bitswap option be enabled or disabled?
I've attached some graphs from routerstats for clarity...
cheers
Graham
GrahamC
Grafter
Posts: 257
Registered: 19-07-2009

Re: Router, Line or the will of BT?

Hi JoJo
that was me alright  Smiley
Yes, go ahead and retrain the line, everything seems to have settled down again, although I don't know why the SNRM was in such a state after the reboot.
I'll keep monitoring throughout the process, just for information and feedback.
cheers
Graham
jojopillo
Grafter
Posts: 9,786
Registered: 16-06-2010

Re: Router, Line or the will of BT?

Will do, Graham.
I'll let you know how it goes.
Jojo Smiley
Community Veteran
Posts: 19,100
Thanks: 437
Fixes: 21
Registered: 31-08-2007

Re: Router, Line or the will of BT?

Hmm, interesting, I would normally have said IMHO, bit swapping should be enabled.
You talk about the SNRM fluctuating, I wouldn't have described it quite like that, it's just the peaks and troughs of the interference itself. If you turn on the average SNRM plotting as well (as I suggested earlier) I'd be very surprised if it wasn't a flat line.
Was bit-swapping on when you took the bits/tone plot (graph 2)? That  graph looks a nice healthy one to me, all the plots look as I would expect, but for one thing, I wouldn't be expecting quite that sort of drop off at the top end if you were that close to the exchange, so I'm beginning to think I can't believe the modem/router attenuation figures.
In normal circumstances, (we are talking 20CN) as you sync with the exchange, DLM is looking for how many bits it can get into each tone dependant on the noise that is present and once that is decided it won't change until a resync. If there is particular strong interference to one tone, eg. a MW broadcast station, then the number of bits per tone are noticeably reduced, (Tone ~232 on your plot suggests to me a local radio station not too far away). With bit swapping, as noise increases the SNRM will drop a bit, but as the noise fluctuates on particular tones the modem will swap bits from tone to tone to try and prevent the SNRM reducing further. That may be a slightly simplistic explanation.
If however, when you are syncing there is a lot of broad spectrum noise eg. perhaps from a poorly supressed electric motor running at a steady speed, or perhaps a better example - a badly designed switch mode power supply, then this could affect all the tones fairly evenly but maybe with the higher tones more so, so you don't initially see anything obviously unusual with a bits/tone plot.
This is a curious one, do you know how far from the exchange you are?
I'm not sure exactly what is going on without more data, you certainly seem capable of looking at this in the right way.
It will be interesting to see what happens with the line retrain.
What one can definitely says is that something started generating interference just after midnight, what, is still a mystery.
jojopillo
Grafter
Posts: 9,786
Registered: 16-06-2010

Re: Router, Line or the will of BT?

Hi Graham,
That was quick.
Attenuation 12.5dB    SNR  9dB    Sync  8128 
Just need to wait for the profile to lift from 6000 now.
Jojo Smiley
GrahamC
Grafter
Posts: 257
Registered: 19-07-2009

Re: Router, Line or the will of BT?

@jJoJo
Cheesy Sure was, don't like to hang about....
was watching on routerstats, and can confirm a synch at 8128, however I seem to have this fluctuating SNRM again. I'll leave well alone for a while and see if it settles, otherwise I'll try switching off and leaving for an hour or so.
@anotherone
This one is very strange, the changes in SNRM didn't start happening until I rebooted the router. Was steady at 15db before, and after the resync it started fluctuating, hence my suggestion that the DSLAM and router are pulling in different directions trying to achieve the same outcome. As I've stated above to JoJo it's doing the same thing now and this is with bitswp disabled in the router. I'll leave for a while to see how things pan out.
cheers
Graham
Community Veteran
Posts: 19,100
Thanks: 437
Fixes: 21
Registered: 31-08-2007

Re: Router, Line or the will of BT?

Well, that's intriguing. The attenuation suggests you are that close to the exchange,  but because of that the SNRM suggests there is a lot of broad spectrum noise present, or there is something bridging the line, and prior to the reset this had caused the Target SNRM to go to 15dB.
Edit: just re-reading the thread to make sure I hadn't missed anything - you said at the beginning you were 1km from the exchange, I should have picked up on that.
Daft question but needs to be asked, you haven't got anything plugged into your line that isn't filtered like a Sky box for example?