VDSL Performance & Tuning

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#719137 18-Nov-2012 19:59

helis:
richms: Speed it set at sync time, so less noise from less people using the internet will give you higher speeds for the same noise margin.

This is what I assumed. But it seems its better to sync at a busy time so that the router picks a speed that suits the worse line condition. This way CRCPM's overall are lower. I generally save doing a reset if i need to until about 7pm.

I get higher speed and worse error count on the ADSL if I sync in the morning, Since I synced in the powercut I have synced at 19 meg, have a 5.5dB margin and it screams along compared to the usual 13 meg on a good day it used to get. The VDSL line crapped out with all the other users coming back online but I think I was getting around 40 with the sync during the powercut compared with 22 I have normally.

Richard rich.ms

helis

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#719362 19-Nov-2012 10:35

SamF: I find that even a <1mbit speed change can affect error rates dramatically.

Well, after a few hours with RFI set to 5 I'm getting more errors! Gonna try RFI 3

EDIT: Same deal with RFI 3 & also back on RFI 1!? I dunno, this RFI setting just seems to make things worse for me!

I honestly have never been able to work out a predictable pattern when it comes to the RFI setting. I would like to know what exactly its there to counteract as I know the couple of times I changed it from default my CRCPM went up not down so I got the idea that maybe if its used when its not needed it works against the quality.

sidefx

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#719396 19-Nov-2012 11:08

richms:

I get higher speed and worse error count on the ADSL if I sync in the morning, Since I synced in the powercut I have synced at 19 meg, have a 5.5dB margin and it screams along compared to the usual 13 meg on a good day it used to get. The VDSL line crapped out with all the other users coming back online but I think I was getting around 40 with the sync during the powercut compared with 22 I have normally.

Perhaps it was just random variations, but comparing the few times I have resynced in the evening\weekend (busy periods) to a couple of early morning weekday resyncs, I seemed to get much better error rates after resyncing early morning weekdays.

Mine is ticking along on max performance Target SNRM (12db down from 14 which I ran for a while) on DLM1 36/10 with CRCPM steady at 0.12.

I still have RFI set one notch to the left and both times I've tried putting it back to max performance error rates have shot right up. I haven't tried it early morning though and have been meaning to.

"I was born not knowing and have had only a little time to change that here and there." | Octopus Energy | Sharesies
- Richard Feynman

mattgreen

133 posts

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#719775 19-Nov-2012 21:34

Got a tweet from Snap letting me know I was scheduled for upgrade today and got home today to find the Fritz happily synced on VDSL2 :))

Well pleased with the speed and if I read the below correctly I'm on DLM1 already. Over double my ADSL2+ sync speed of 16-17Mbps!

Just after I grabbed these screenshots my wife accidentally powercycled the Fritz and I've resync'd at 44.5Mbps with SNRM of 12db. Not getting any CRC's in the last 5 mins so I'm hopeful that DLM will learn to leave me there.

Went from 6db line attenuation on ADSL2+ to 10db on VDSL2 which seems about normal. I haven't bothered disconnecting the only other jack in the house and it's not looking like it's worth the cup of tea I'd have to give up to go out and do it :)

helis

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#719804 19-Nov-2012 22:24

mattgreen: Got a tweet from Snap letting me know I was scheduled for upgrade today and got home today to find the Fritz happily synced on VDSL2 :))

Well pleased with the speed and if I read the below correctly I'm on DLM1 already. Over double my ADSL2+ sync speed of 16-17Mbps!

Just after I grabbed these screenshots my wife accidentally powercycled the Fritz and I've resync'd at 44.5Mbps with SNRM of 12db. Not getting any CRC's in the last 5 mins so I'm hopeful that DLM will learn to leave me there.

Went from 6db line attenuation on ADSL2+ to 10db on VDSL2 which seems about normal. I haven't bothered disconnecting the only other jack in the house and it's not looking like it's worth the cup of tea I'd have to give up to go out and do it :)

DLM1 straight away? First time thats happened here?

Your error rate appears to be very high though. Exactly what mine was when I was put on DLM1 and it didn't last very long. I'd say you'll be off DLM1 with in 48 hours. Thats just my guess though. Im amazed you were put on it so fast.

SamF

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#719854 20-Nov-2012 00:05

I have discovered something interesting about the RFI setting; if you are having issues with increased error rates after changing the RFI setting (even after setting it back to RFI 1 / Max Performance), you need to unplug your router and leave it unplugged for at least 5 minutes before plugging it in again. I tried briefly unplugging my router to try to clear this setting, but it made no difference. It wasn't until I unplugged it for a few minutes that my error rates returned to pre-RFI levels. I have confirmed this a number of times now.

Note that when I say 'unplug' I'm referring to the power, however since it's a bit odd that the router itself would 'remember' the setting even after a power cycle, it may be that it's the cabinet end which needs 'resetting', and by disconnecting the line for a few minutes this is achieved. What I'm getting at is that you may be able to achieve the same thing by simply unplugging the line for a few mins. I'll try that next time.

EDIT: Confirmed, disconnecting the line for 5 minutes doesn't resolve the issue; power down for 5 mins is the only way! Weird!

mattgreen

133 posts

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#719922 20-Nov-2012 09:08

Looking at my emails last night I noticed the Fritz got a new IP at around 10:30am then again at around 5:30pm (I have push service enabled). I'm guessing the first one was when VDSL was enabled so it's possible I wasn't on DLM1 for the first few hours.

Have just checked now and had no syncs over night. Still on DLM1 with FECPM=15 and CRCPM=1. SNRM is sitting on 12db.

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sidefx

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#719941 20-Nov-2012 09:36

Generally I think everyone has been gettign DLM resyncs at 4:10am; I think DLM can do them at other times, but not sure if anyone has actually had a DLM change at other times.

That CRCPM would be worrying me, but leave it and see what happens. I definitely would have disconnected all other jackpoints too, VDSL is just so sensitive. Looks like some very nice stats though!

"I was born not knowing and have had only a little time to change that here and there." | Octopus Energy | Sharesies
- Richard Feynman

mattgreen

133 posts

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#719987 20-Nov-2012 11:04

Yeah I'd read the first 10 pages and got the impression a CRCPM up to 3 wasn't a biggie. With 44.5Mbps I didn't see the point in fiddling with the wiring to get more speed. But looking through the thread it seems people later decided a sub 0.5 CRCPM was a better target. If I get time I might nuke the second jack tonight and see if it makes any difference to the CRCPM.

helis

96 posts

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#719990 20-Nov-2012 11:07

mattgreen: Yeah I'd read the first 10 pages and got the impression a CRCPM up to 3 wasn't a biggie. With 44.5Mbps I didn't see the point in fiddling with the wiring to get more speed. But looking through the thread it seems people later decided a sub 0.5 CRCPM was a better target. If I get time I might nuke the second jack tonight and see if it makes any difference to the CRCPM.

Don't get confused by the CRCPM. 0.3-0.4 is possibly the max DLM1 can handle. The "0." is very important. If you are seeing 0.3 than thats cool but if you are seeing 1 - 3 then you wont stay on DLM1 for long.

A CRCPM of 3 is very very bad. It would be considered a big issue.

mattgreen

133 posts

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#720008 20-Nov-2012 11:42

Ahh then it must be a typo in the first post.

Non-Remedial Errors (CRC):
CRC errors occur when FEC is not able to repair corruption in the data transmission. These are the errors that you need to be concerned about. The closer this figure is to 0 the better, but early results indicate that it is possible to have a 'CRC Per Minute' (CRCPM) rate of up to 3 and still maintain a stable line on the DLM-1 profile (see the 'Dynamic Line Management' section below).

sidefx

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#720011 20-Nov-2012 11:49

The key there is the "early results" bit - a fair bit of the stuff (particularly numbers) in this thread is based on annecdotal evidence from a fairly small sample size. (and I think there was also period where DLM was just behaving oddly and barely changed anyones profiles even with very high CRC error rates. Or maybe they've just tweaked the DLM parameters since then)

But I believe since then we've "collected more data" and sort of come to the conclusion that anything above 0.4 or so is definitely bad for CRCPM. Though it also appears (and this is just my theory - not based on anything other than annecdotal evidence) that once DLM settles on a profile during the first 10 days it will then leave you on it for a good 6 weeks or so before making another change - perhaps to collect more data.

"I was born not knowing and have had only a little time to change that here and there." | Octopus Energy | Sharesies
- Richard Feynman

stevehodge

393 posts

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#720197 20-Nov-2012 16:17

mattgreen: Yeah I'd read the first 10 pages and got the impression a CRCPM up to 3 wasn't a biggie. With 44.5Mbps I didn't see the point in fiddling with the wiring to get more speed. But looking through the thread it seems people later decided a sub 0.5 CRCPM was a better target. If I get time I might nuke the second jack tonight and see if it makes any difference to the CRCPM.

You might have been looking at one of my earlier posts. When I first went onto DLM-1 I had a CRC error rate of around 2-3 per minute. I stayed on DLM-1 for a month before it downgraded me to DLM-2. But that was after the initial 10 days - DLM usually makes changes more regularly during that first period (every 2-3 days) and then after that it seems to only look at the line every 4 weeks.

helis: Don't get confused by the CRCPM. 0.3-0.4 is possibly the max DLM1 can handle. The "0." is very important. If you are seeing 0.3 than thats cool but if you are seeing 1 - 3 then you wont stay on DLM1 for long.

The last time my Fritz was reset I went from 0.3 CRC/min to 2-3 CRC/min. That was two weeks ago. I am still on DLM-1. If DLM is not making rapid changes then you can stay on DLM-1 with bad error rates for quite some time. I expect DLM will look at my profile at the end of the month, and I'll probably be downgraded then.

A CRCPM of 3 is very very bad. It would be considered a big issue.

So long as you are not losing sync it is a big issue only if 0ms latency is important to you.

SamF

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#720976 21-Nov-2012 21:13

mattgreen: Ahh then it must be a typo in the first post.

Non-Remedial Errors (CRC):
CRC errors occur when FEC is not able to repair corruption in the data transmission. These are the errors that you need to be concerned about. The closer this figure is to 0 the better, but early results indicate that it is possible to have a 'CRC Per Minute' (CRCPM) rate of up to 3 and still maintain a stable line on the DLM-1 profile (see the 'Dynamic Line Management' section below).

Oops!! Time for a bit of revision methinks!! Sorry! :/

mattgreen

133 posts

Master Geek

#721043 21-Nov-2012 23:21

Not a problem at all Sam. No need to apologise at all. That's a great summary and saved me wading through all 40 pages!

Interestingly I didn't get the expected resync last night. So I'm still sitting on DLM1 with CRCPM of 1 and SNRM of 11 or 12 depeding on how it feels.

Guess we'll see what happens overnight tonight.

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