VDSL Performance & Tuning

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90 posts

Master Geek

Reply # 699501 11-Oct-2012 09:44
Thats a good idea sidefx, ill try that as the next option if it craps itself again. Snap have not owned up to making any changes but it feels like something has potentially been fixed. Sitting on 15 hours uptime with a perfect sync rate and 0 CRC errors. Very few FEC errors. And SNR is holding at a steady 14db. Attenuation is still at 2db.

SamF

826 posts

Ultimate Geek

Trusted

Reply # 699716 11-Oct-2012 14:53
Well! I noticed this morning that there had been a 4am resync on my connection. I was thinking that my 35+ resyncs last week might finally have caught up with me and I was now on a worse DLM profile, but no! I now have a MASSIVE decrease in CRCs!! DLM profile and sync rate both appear to be the same, the only difference I can spot is that Bitswap is on (which it has been before, without such dramatic results). RFI is still on level 5 (left it on this after my earlier experimentation), so maybe this has finally kicked in? Still, I can't help but think there's some other behind the scenes stuff going on based on the 4am resync. If so, Snap can't tell me what this might be however. I'd try turning off RFI to see if that makes any difference, but I'm worried I won't be able to turn it on again! :/ I found some more info on bitswapping here. So pretty straight forward, but nothing that hasn't been working before. I wonder how long the fritz 'remembers' bitswapped carriers? Hopefully whatever it is is permanent now!

helis

84 posts

Master Geek

Reply # 699750 11-Oct-2012 15:42
@SamF Is it possible you have moved to a new DLM which isn't showing correctly. Someone mentioned a while back that DLM should only change by one each time but a lot of people including myself saw jumps from DLM6 to DLM2 bypassing DLM4 yet the day after DLM2 it would resync at 4am with no change possibly moving to the actual DLM2 profile. So maybe you are on DLM4 now which could explain the drop in errors but your lag still being 8ms. Out of interest have you tried setting your SNR to max stability and if so what kind of errors and sync speed do you get? I honestly wish I had set my SNR to max stability from day 1 until after the 10 day phase was complete than moved it up slowly. almost 2 days now and I'm on 0 CRCPM. I lost 6Mbps but I'll hopefully get that back once I do the cat5e run this weekend.

SamF

826 posts

Ultimate Geek

Trusted

Reply # 699807 11-Oct-2012 16:39
I haven't heard of DLM changes not being reflected in the status page before tbh. As for SNRM tweaks, I should have mentioned, I've gone back to stock settings while I'm testing RFI, plus I was getting snap to look at my line so i wanted to show its true state. I'll go back to a higher SNRM later.

varix

90 posts

Master Geek

Reply # 699824 11-Oct-2012 16:54
So today spoke to Snap again, and I must say Snap are amazing, their call centre staff are so helpful. Talking to another human rather than talking to some person sitting in front of a script. Snap cant really do much until I get a splitter in as Chorus dont want to have anything to do with it. So, I went and spent $20 on a VDSL splitter from Computer Dynamics and got some gel crimps. Came home and installed it in about 10 minutes. Cant beleave Chorus charge $400 for that haha. Modem came back up and sync is looking good, although FEC errors might be doing their usual spike again, they have been increasing constantly since last sync. See if they keep going up into the millions like they have done in the past.

stevehodge

148 posts

Master Geek

Reply # 699857 11-Oct-2012 18:20
SamF: I haven't heard of DLM changes not being reflected in the status page before tbh. I've yet to see anyone with INP of 1.0. So either DLM-4 and DLM-5 are not used in NZ or the Fritz!Box doesn't correctly display INP of 1.0. Given that several people have reported DLM resyncs with no change to the latency/INP, and all those "do nothing" resyncs seem to happen on DLM-2, I think it's reasonable to conclude that DLM-4 is in use and the Fritz!Box misreports it as DLM-2. Napster mentioned this on page 6 and I've commented on it before as well.

SamF

826 posts

Ultimate Geek

Trusted

Reply # 699955 11-Oct-2012 22:06
I've definitely seen INP at 1.0 on my connection (also mentioned on Page 6).

SamF

826 posts

Ultimate Geek

Trusted

Reply # 699982 11-Oct-2012 23:14
Ok, so I'm a glutton for punishment, but my curiosity got the better of me and I tried changing RFI back to 1 on my connection. There was an immediate increase in FECs, but no measurable increase in CRCs. Swapping around different RFI levels made no measurable difference and I'm now back where I started with RFI at 5. FECs are still significantly elevated compared to where I started tonight (1500 up from 70). Bitswap is still on. Based on this, I suspect that the major decrease in CRC errors since this morning's resync was due to bitswap. I am speculating that maybe in order to turn bitswap on a resync is required? I'm going to leave it overnight to see if FECs settle down and then up the SNRM a bit to hopefully speed up DLM profile upgrades. Oh, I found out today that Snap spoke to Chorus about my line and Chorus' theory was that my router may be faulty... I hadn't considered that! Might have to try a new router anyway, if only to prove that the router isn't at fault and get Chorus to do something useful... Also, since making my original post, my CRCs have jumped back up to their original high levels of ~15pm :( Bitswap is still on and RFI is at 5. New theory is to leave it alone for a few days and see if the 'magical' low error condition comes back...

stevehodge

148 posts

Master Geek

Reply # 699991 12-Oct-2012 00:21
SamF: I've definitely seen INP at 1.0 on my connection (also mentioned on Page 6). Ok, so that proves DLM-4 is in use and the Fritz!Box sometimes reports it correctly. But no one else has reported INP of 1.0 and plenty of people have seen DLM resyncs while on DLM-2 with no apparent change in DLM level. So I think the most likely scenario is still that the Fritz!Box usually misreports DLM-4 and those resyncs were actually changes between DLM-2 and DLM-4.

stevehodge

148 posts

Master Geek

Reply # 699993 12-Oct-2012 00:29
SamF: Based on this, I suspect that the major decrease in CRC errors since this morning's resync was due to bitswap. I am speculating that maybe in order to turn bitswap on a resync is required? I've seen bitswapped turned on without a resync. For me it seems to usually start out off when I resync and then come on sometime later. It does seem to make a difference. After a week of DLM-1 my CRC errors were about half what they started out as and the difference seems to have been bitswap. As soon as I resynced after changing the RFI setting they shot up again. Weirdly though my CRC errors seem to have increased over the last day or so. They were 0.15, now they are 0.23.

Cadriel

122 posts

Master Geek

Reply # 700040 12-Oct-2012 09:32
So - at 4am this morning I was put on to DLM-1. Yay.. My CRC per minute jumped to 0.9 though. I've gone ahead and dropped my SNR by another notch. Is this the correct way I should proceed?

sidefx

1060 posts

Uber Geek

Reply # 700046 12-Oct-2012 09:37
Yeah I probably would; 0.9 seems a bit high. I assume that was after giving it a few hours to settle\average out though? Has dropping it another notch lowered the CRC error rate?

Cadriel

122 posts

Master Geek

Reply # 700047 12-Oct-2012 09:39
Yeah - that was me getting around to checking it about 10 minutes ago. I've just dropped the SNR now.. so it hasn't had time to really pick up yet. I'll keep an eye on it over the next hour or so and drop it another notch if I need to. I essentially just have to get it under 0.3 right?

SamF

826 posts

Ultimate Geek

Trusted

Reply # 700049 12-Oct-2012 09:43
The jury is out on exactly what level you need to keep your CRCs under, but it's either 0.40 or 0.25.

sidefx

1060 posts

Uber Geek

Reply # 700050 12-Oct-2012 09:48
Cadriel: I essentially just have to get it under 0.3 right? We don't know the exact parameters or levels that cause DLM changes, but yeah that seems to be about right based on the observed behaviour in this thread; I tend to aim even lower, around 0.1 - purely because I value lower latency more than the extra 3-6mbit of downstream sync rate\throughput; it's not doing much for you on international throughput anyway.

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