Broadband Related > FTTC and FTTP Issues
Sync drops by a third
22over7:
Something fairly catastrophic happened to my long-time stable line before 7:50pm Friday giving DS speedtests of just of 60Mbps; afterwards, 40Mbps. The upload (17Mbps-ish) took a small hit too. As far as I could tell, by error-rates were fairly normal.
The event looked very bizarre on my SNRM dslwebstats (I'm SandReck). The graph had a huge spike, and even went negative (?!). I don't know what to think. I had the dslwebstats feed off for a day or so, then when I realised, clicked the record button. All hell broke loose. Total coincidence? Nobody seemed to have been fiddling with by Huawei cabinet. I use an unlocked HG612. I powered all my equipment off, waited a bit, then on again. No joy.
Before, I was 16/1 interleaved. Now I'm 1/8 interleaved. My SNRM margins were about 7.4 db down, 13.6 up; now they're almost identical, about 6.3 or 6.4. with a pronounced "wiggle" -- about 3 waves in 10 minutes. Maybe the US SNRM is drifting a bit higher.
I just wondered, if any of the network gurus on this form can see my (SandReck's) dslwebstats data, and enlighten me, if possible, as to what-the-hell-might-have happened to provoke such a dismaying, sudden, deterioration? Internet access seems subjectively rather crummy now, though I can appreciate many people have it lots worse.
I'm with Plusnet, for almost 3 years. They seem to dislike having people on 80/20, and very often people on such a package find themselves misconfigured on 40/2 or something like that (I'm something consistent with 40/20). I'm hoping it's some misconfiguration their end. I've raised a fault, but have no idea when/if they'll take a look. Anyway, here, I'm just after a little enlightenment. I can dig out current data quite easily (I've attached some post-apocalyptic modem stats), but my line had been so stable before, that I'm not sure I can remember much about its former state (except via historical dslwebstats data).
kitz:
If I had to guess the symptoms look kind of crosstalk related. However that is one heck of a hit to take all at once.
Your downstream SNRm went from 7.4dB to -2.8 (10.2)
Your upstream SNRM went from 13.2dB to 6.3dB
The upward spike is interesting, thats the sort of thing you could expect to see if a whole lot of users suddenly got knocked offline and had to resync. Some of the BCM chipsets such as those used by the HG612/Zyxel seem to come back up much faster than say the HomeHub5a.
However the corresponding spike in your max attainable doesnt quite give the headroom I would have expected if your downstream SNRm really was at 14dB so Im not quite sure exactly what happened there.
The spikes indicate that what ever affected you, also had an impact on some of your neighbouring lines.
19:38 is a bit of an odd time for a new disturber to appear, but it is possible that someone got FTTC swapped over during the day but it was a self install and they didnt switch their modem on until that time when they got home from work.
What could have happened if your modem is happy doing its thing, neighbour turns on their modem. Bam crosstalk which immediately makes your SNR drop to minus 2.8dB. The line cant hold at such a negative figure so attempts to resync at the target of 6dB which accounts for your loss of speed.
Although its not unusual for crosstalk to suddenly knock 10Mb from a lines max attainable, I dont think Ive seen what looks like one single disturber take 20Mbps off a line that was previously syncing at around 60Mbps.
This isnt anything to do with Plusnet configuration, they have no control over your SNRm or sync speed (other than provision type ie 80/20,40/2). Such a drop does however need investigating so you will have to go through the fault process :(
----
PS note for others. Ive not looked at all stats or params. Only concentrated on main figures and not any config params.
QLN is a bit messy... some noise... and also upstream crosstalk. Slight signs of crosstalk bump at tone 3500 onwards. Noise in D1 & D2 makes it a bit impossible to spot any obvious crosstalk in those carriers.
Hlog looks fine indicating physical line ok. Slight bump also around 3500 but not anything Im too concerned about.
Attaching zoom of SNRM
Im only able to type one handed atm so its taken me a while to make this post and I need to get to bed myself.
ktz392837:
--- Quote from: 22over7 on April 17, 2017, 09:22:03 PM ---Something fairly catastrophic happened to my long-time stable line before 7:50pm Friday giving DS speedtests of just of 60Mbps; afterwards, 40Mbps.
--- End quote ---
I have a (perhaps two) major crosstalk disturbers that has a similar impact 6-7db each. Overall I have lost 40% due to crosstalk and as I am on ECI cabinet I do not know if it can worse - I hope not but not convinced unless they get GINP/3db working for at least a little compensation.
22over7:
Many thanks for the replies, especially for pointing me at things that may be most relevant. I'll try to assimilate some of the (copious) relevant information on this site.
My cabinet (serves 427 according to www.telecom-tariffs.co.uk/codelook.htm) and PCP are about 200 metres away as the crow flies, but maybe 600 away electrically,
going literally round the houses and ending with a long cable run along back-garden walls, ending in a pole serving at least 8 properties. I guess crosstalk can
occur anywhere in/beyond the DSLAM though. I'll try to get calamity-anecdotes about last Thursday from the neighbours I'm still speaking to. And wait for Plusnet's fault-team. And investigate what Virgin can offer.
Just for lolz, one of the properties passed was a cannabis farm, when my line was at its best (just south of 70Mbps on speedtests).
NewtronStar:
Your Bandplan Downstream and Upstream are still the same but the bits per tone have lowered this will cause a lower sync rate than you were used to, going to show your bit tones before and after
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