New BB FEC errors

Tephnos said:
Quick question for you Alec, since you seem to know quite a bit about all of this - how many errors are you getting per day?

My line is pretty quiet during the day but then from 9pm-1am or so every single night it will spike like crazy (relatively), with the CRC jumping to 30-300 (maybe once it will hit 2000!) up and down until 1am where it'll suddenly quieten down again.

Any reason why its always between that timeframe? DLM won't hit me for it because BT's ES limit is 2880 and that error spike leaves be around 1400-1600 by the end of the day according to my telnet stats. I'd just like to know what could be a common cause for this type of thing, since it definitely scares me that a bad day could have DLM hit me.
Click to expand...

Sorry for the delay in replying.

Is this ADSL or VDSL - I'll assume ADSL as that's what the OP is on.

At night interference increases in general, which means your line is able to repel less interference overall. Interference will cause packets to be dropped which then have to be resent - these are the errors you're seeing.

In the daytime the background interference is relatively low so your line does a pretty good job of repelling most of it.

Have you got interleaving turned on or are you on fastpath? Fastpath doesn't have any error correction so any dropped packets will cause errors. Interleaving will reduce the errors by using error correction, at the expense of latency (it will increase).

On VDSL, G.INP is being rolled out which allows interleaving to be reduced significantly so latency is reduced but the line is also much better at dealing with interference so the line errors less overall.

In my case, I've gone from several hundred CRCs per day on VDSL, to zero with G.INP enabled. I've gone from 30ms pings to 8ms pings because interleaving has been reduced to a depth of 4. I still get FECs (particuarly at night like you do) but they're all corrected so DLM won't intervene.

Shame my connection keeps dropping and I'm probably getting less sync than I should but TalkTalk's UK team are investigating that - slowly.
 
AlecR said:
Sorry for the delay in replying.

Is this ADSL or VDSL - I'll assume ADSL as that's what the OP is on.

At night interference increases in general, which means your line is able to repel less interference overall. Interference will cause packets to be dropped which then have to be resent - these are the errors you're seeing.

In the daytime the background interference is relatively low so your line does a pretty good job of repelling most of it.

Have you got interleaving turned on or are you on fastpath? Fastpath doesn't have any error correction so any dropped packets will cause errors. Interleaving will reduce the errors by using error correction, at the expense of latency (it will increase).

On VDSL, G.INP is being rolled out which allows interleaving to be reduced significantly so latency is reduced but the line is also much better at dealing with interference so the line errors less overall.

In my case, I've gone from several hundred CRCs per day on VDSL, to zero with G.INP enabled. I've gone from 30ms pings to 8ms pings because interleaving has been reduced to a depth of 4. I still get FECs (particuarly at night like you do) but they're all corrected so DLM won't intervene.

Shame my connection keeps dropping and I'm probably getting less sync than I should but TalkTalk's UK team are investigating that - slowly.
Click to expand...

I'm on VDSL mate.

Since I posted that, I had a horrible night with 4,000+ Error seconds, DLM turned on and ruined my ping, so I moaned at BT and they've identified some kind of fault, so we'll see how that goes. I don't think I should go from a few hundred ES over a day to a few thousand in the space of 4/5 hours - that's crap!

No G.INP on my cab yet so I'm refusing to have DLM ruin my profile. My CRCs were in thousands per day, haha. Connection was rock solid though until DLM killed it for a second to ruin my profile.
 
I suspect you might have an HR fault like the OP.

Like I say it is normal for errors to increase at night but the level I suppose is disputed.

What does your SNRM look like at night?

I would suggest uploading the stats to MyDSLWebStats so I (and others) can take a look at the line.
 
AlecR said:
I suspect you might have an HR fault like the OP.

Like I say it is normal for errors to increase at night but the level I suppose is disputed.

What does your SNRM look like at night?

I would suggest uploading the stats to MyDSLWebStats so I (and others) can take a look at the line.
Click to expand...

My stats are up on there already. If you can, look at stats for nostos156. You'd have to look a fair few days back, before DLM turned on. :)

The BT rep said they found a DSL/BRAS mismatch, dunno if that'd be related.
 
AlecR said:
You're on BT Infinity I'm guessing? If I'm right, there couldn't be a mismatch as the BRAS profile (IP profile) is updated as soon as you resync :confused:

tldr: sounds like rubbish I'm afraid.
Click to expand...

Yeah, I am.

No idea but they've sent an engineer out anyway so it wasn't like they were fobbing me off. I'll just have to explain in detail what happens when he shows up.

(Oh, and SNR margin on the downstream does drop below 6 when the line errors went bad)
 
An engineer visit will be good - I'll be interested to see what they say.

It is normal for the SNRM to drop at night as like I say interference increases (that's why you have an SNRM margin so the line can remain connected at night) but the amount of errors you should get is disputed.

I'm surprised your interleaving depth isn't large to counteract the errors though.
 
Well, DLM turned it on to 1355+ to do exactly that, and hasn't turned off since it happened.

I'm miffed about that because the last thing I want is horrible pings, worse than ADSL. BT routing is already terrible this far up north as it is. I dispute the errors because there's no way imo that I should go from a few hundred during the course of the entire day to a 1000/2000+ in the space of 4-5 hours. Not buying that. Interference is messing with something that's already flaky.
 
Do you have any crackling on the phone line?

I'm thinking you either have an HR fault or a noisy line. The first issue can be resolved fairly easily, the second will take a lot of effort - you'll need a pair change which may or may not make a difference.
 
AlecR said:
Do you have any crackling on the phone line?

I'm thinking you either have an HR fault or a noisy line. The first issue can be resolved fairly easily, the second will take a lot of effort - you'll need a pair change which may or may not make a difference.
Click to expand...

I did the quiet line test and heard no crackling. If I tried really hard I might have heard a tiny hiss but... that's probably the blood rushing through my ear. :D
 
Well, engineer showed up today and found bugger all. :(

I explained to him when and how they happened and he basically said "Because they happen at night and my tests are fine during the day there is nothing we can really do since we can't check it at that time."

God dammit. Where's my G.INP.
 
AlecR said:
That's typical OR I'm afraid.

You can keep raising it and getting engineers until you get one who will do something but I don't know if you want to go through that much effort.
Click to expand...

Problem is if they don't find anything during the day (which they never will) then what can I exactly do?
 
It's the ISP that will request a Tie pair Shift. Usually as a last resort as the port that he's using will be marked as 'bad' and won't be reused in future.
 
You must log in or register to reply here.
Back
Top Bottom