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[andatche]

I've had an FTTC service for about a week now, after being the 5th customer connected to our newly enabled Huawei 288 cab. I've been monitoring line stats since via the unlocked HG612 and SNRM has remained steady at ~8.6/23.2 for DS/US respectively for the week so far. Today I noticed a largish step drop in SNRM for both DS and US, which are now ~5.9/17.7 respectively, see graphs below.

This has unfortunately pushed the DS attainable rate below 80mbps now, a bit disappointing considering we are <100m from the cabinet. Is such a large drop accountable to a (presumably close) neighbour being newly connected? I'm guessing the brief spikes back to the previous levels are presumably them rebooting their CPE? I can't see any change in power for either DS or US.

[kitz]

Hi and welcome to the forum.

I'm afraid that graph does indeed display the classic signs of crosstalk, and as you guessed the spikes will likely be a router resync.

Aside from that your snr looks lovely and flat.  Your h-log is beautiful.. so it looks like your physical line is good.  Your QLN paints a different picture .  So yes I'm pretty sure it's crosstalk. 

If crosstalk is going to show anywhere it will be in the Qln.  Compare your qln to mine - don't compare snrm as I have a fault atm on my upstream.   But if you look at my qln and note the shape.  The shallow dish effect centered mid D1 and a couple in D2 is where I'm mostly being hit by cross talk.   I've circa 23mb from my headline attainable due to crosstalk.  Now look at yours, so it looks like you have at least one heavy disturber. 

[Chrysalis]

I agree its crosstalk, I dont think your line is 100m tho, I am basing that comment on the reported attenuation from the modem.  It is higher than mine and I was told my line is close to 400m.  I guess your line routing isnt as direct as you thought it was.

Sadly the QLN wont load currently for me on tony's site so cannot comment on that, I think he does maintenance at 1am so will check later.

--edit--

Ok it loaded now, to me your D3 QLN is still good but on D1 is probably one of the worst crosstalk I seen it is hitting -105.  So the bad news is I think you have more crosstalk to come as D3 can definitely get worse, but my D3 held on for over a year after my D1 got battered quickly, so it may not happen for a while.  Your starting attainable wasnt that great either only 87mbit, I wish you luck but there may well be more to come.  As an example I started at 110 and at one point hit 50, but am now on 73 after a pair swap.

[andatche]

Thanks for the insight and confirmation of my suspicions.

Ok it loaded now, to me your D3 QLN is still good but on D1 is probably one of the worst crosstalk I seen it is hitting -105.  So the bad news is I think you have more crosstalk to come as D3 can definitely get worse, but my D3 held on for over a year after my D1 got battered quickly, so it may not happen for a while.  Your starting attainable wasnt that great either only 87mbit, I wish you luck but there may well be more to come.  As an example I started at 110 and at one point hit 50, but am now on 73 after a pair swap.

Interesting that you point this out. I've taken a quick look through the historic QLN graphs back to the point the service was initially provisioned and there doesn't seem to have been any change, so it looks like this has been the case since at least the day of provisioning or perhaps even prior to that. Could this be accounted to crosstalk from ADSL2+, given that it seems worst up until tone 512? Could this be attributed to anything else?

[Chrysalis]

I would think it unusual to have that sharp snrm drop without some form of increase on the QLN graph to indicate increased crosstalk.  Can adsl cause that level of crosstalk? I think yes if you close to exchange as the adsl signal is still strong then.

[andatche]

Ah, it seems that QLN is only measured during the sync process. I haven't had a resync since before the SNRM drop, but my sync rate is now above the attainable rate so I expect I will loose sync at some point in the near future, I'll check again then.

We are indeed close to the exchange (the building is <100m away) and until a few months ago this was an EO line. It was moved to a newly provisioned PCP built directly outside of the exchange recently, which is connected to an FTTC cab about another 50m away.

I do wonder if we've had a noise/interference problem since before the FTTC migration, as we were never able to acheive >18mbps sync on ADSL2+ despite decent noise margin and attenuation figures. Unfortunately it wasn't possible to collect any of the more interesting line stats from my old ADSL2+ modem though, so this is purely speculation.

[Chrysalis]

ok yep you right its only during sync, so next time you sync expect it to change.