Demystifying VDSL DLM

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#1613919 18-Aug-2016 18:58

dclegg:

As suspected, I have now confirmed that my Asus router has nothing to do with it.

Approximately 7:20PM last night, the modem dropped its connection. When it reconnected, it obtained speeds of 6.7Mbps/400Kbps (according to nperf speed test; modem UI timed out when attempting to query it).

This morning, I noticed the modem had reconnected at around 4:15AM. It had sync speeds of 11Mbps/800Kbps. I rebooted the modem, and ended up with sync speeds of 29Mbps/2Mbps. As per Chorus' advice, I rebooted it a second time. This is currently giving me sync speeds of 10Mbps/1Mbps.

I have forwarded all my recent diagnostics to Spark, so I guess the ball is back in their court.

i still have a feeling dodgy modem is the end all considering the wiring has been dealt with.

I had one go bad, in the time it took me to drive to a new house, literally a 2 min drive even in an anti-static bag! - that annoyed me something chronic to problem solve!

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dclegg

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#1614060 19-Aug-2016 08:12

hio77:

i still have a feeling dodgy modem is the end all considering the wiring has been dealt with.

It's possible, and I'm wondering whether the pragmatic next step may be to purchase another one (currently leaning towards the Draytek Vigor 130, as I successfully used the 120 with my ADSL connection).

For what it's worth, here's the latest update from Spark:

Interesting that the connect rate vary so greatly, normally we would put that down to a faulty main splitter but it has been replaced so recently that this would be almost impossible.

Normally we would suggest a port change at the exchange which has been completed back on the 27/07/2016 so again this is not likely the root cause of the issue. We could have a different class of technician come and inspect the cabling between the exchange and the address.

At the moment the line is stating a 'Good line test' result however attentuation on the line is higher than VDSL is recommended to run on.
This would be the next logical thing to check as the data port, equipment and master splitter has been replaced, even though the line is stating it is a 'good line' in the synthetic test its the only link in the chain that has not really been investigated.

And here are the modem stats from this morning

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#1614378 19-Aug-2016 14:41

One change I just noticed today is that my upstream sync stats are far worse than what I was getting prior to the last Chorus visit (when they swapped the master spliiter). When things went south, I'd have upstream sync stats of around 3Mbps. Downstream stats are better though, with an improvement from the 6Mbps I used to get.

Now when things degrade (which is most of the time, since the Chorus visit), our upstream sync speed is 500Kbps or worse, but downstream stats are usually around 8Mbps.

Here's an attached sampling of stats from the last few days. The two to the left are after Chorus' last visit, with the two to the right from before that.

The case is being investigated by Chorus again on Monday. Here's hoping they can finally get to the bottom of it. If they still have no joy, I may bite the bullet and purchase a dedicated VDSL modem. But I don't want to do that until they've had a chance to perform the line test they're scheduled to do.

Jase2985

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#1614436 19-Aug-2016 16:02

where i the country are you?

i have an old spark technicolour TG589v2 VDSL modem in auckland you could borrow to test

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#1614438 19-Aug-2016 16:05

Jase2985:

where i the country are you?

i have an old spark technicolour TG589v2 VDSL modem in auckland you could borrow to test

West Auckland. Thanks for the offer. I'll PM you if I think it may be helpful, depending on how Chorus get on.

hio77

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#1614439 19-Aug-2016 16:09

dclegg:

West Auckland. Thanks for the offer. I'll PM you if I think it may be helpful, depending on how Chorus get on.

Didn't realise you were that close, i have a few vdsl modems floating around here if need be too.

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#1614447 19-Aug-2016 16:19

i take it you havent tried a new one yet?

would have though you would have wanted to rule out all your own/home stuff first

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dclegg

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#1614450 19-Aug-2016 16:26

Jase2985:

i take it you havent tried a new one yet?

would have though you would have wanted to rule out all your own/home stuff first

I've tried two different modems, although they were both the same model (Spark supplied Huawei HG630b).

The reason I don't want to try another modem just yet is that Chorus are currently investigating the line between my house and the Exchange (a van was outside about an hour ago). They are due to complete this by early next week. Rather than introduce multiple variables, I'll wait to see what Chorus find before trying anything else.

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#1614455 19-Aug-2016 16:41

dclegg:

Jase2985:

i take it you havent tried a new one yet?

would have though you would have wanted to rule out all your own/home stuff first

I've tried two different modems, although they were both the same model (Spark supplied Huawei HG630b).

The reason I don't want to try another modem just yet is that Chorus are currently investigating the line between my house and the Exchange (a van was outside about an hour ago). They are due to complete this by early next week. Rather than introduce multiple variables, I'll wait to see what Chorus find before trying anything else.

Yes, its best you wait keeping things status quo first while they run their tests.

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dclegg

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#1615700 22-Aug-2016 12:13

Chorus visit no. 4. He found no fault with our internal wiring or the wiring to the Exchange. He replaced the master splitter again (third one in 6 weeks). He also said that he was going to assign me a new port in the Exchange (but he also said he'd ring when he's done that, but that never happened). Not that I'm overly excited about the prospect, as a previous Chorus visit resulted in a new port, with no change in stability.

One question I do have though is around the FEC rate. I've been connected for around an hour, and I have the following stats. Is that downstream FEC rate abnormally high, or is that sort of level per hour reasonably normal?

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#1615820 22-Aug-2016 14:42

i believe FEC's are ok its the CRC ones you dont want

Remedial Errors (FEC):
FEC stands for 'Forward Error Correction' which is a method of correcting errors introduced during data transmission without having to re-send any data. These errors have frequently been observed from as low as 30 to as high as 2000 per minute but do not indicate any issues to be concerned about. *6

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 from our testing it appears that it is possible to have a 'CRC Per Minute' (CRCPM) rate of up to 10 and still maintain a stable line on the DLM-1 profile (see the 'Dynamic Line Management' section below).

http://www.geekzone.co.nz/forums.asp?topicid=105744

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#1615965 22-Aug-2016 18:16

Jase2985:

i believe FEC's are ok its the CRC ones you dont want

Generally yes.

there is a point where FECs do cause you trouble, Remember FECs are corrected on the modem itself, so it can all go down hill if too high.

I dont think the FEC rate there is overly too high, kinda concerning they are not properly investigating your case at this point.

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#1615981 22-Aug-2016 19:17

thats 203 per minute or about 4 per second.

dclegg

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#1616137 23-Aug-2016 08:23

So now I know that it takes more than four visits to get a VDSL installation working correctly. Internet went down last night, and now is synching at 16Mbps/76Kbps.

The 16Mbps download sync rate is a poor indicator though, as we're getting extremely poor performance across the board when actually attempting to use the connection. And some things (such as running a Speedtest test) just don't work at all.

The frustrating thing is that this is a reasonably new development, which only started occurring after the second Chorus visit. Prior to that, we'd have performance degradations to approximately 6Mbps/3Mbps. Not ideal, but nowhere near as debilitating as what we now have.

One thing that may be a bit of a clue was that when we lost connectivity last night, it happened directly after the phone rang. Is it possible that the phone line can do that, now that we have a master splitter installed? It's a characteristic that our old ADSL modem used to consistently exhibit, but I never got around to getting it looked into.

Anyway, I have to dash. Need to ring the Chorus tech to tell him he's not done here yet....

hio77

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#1616256 23-Aug-2016 11:57

dclegg:

So now I know that it takes more than four visits to get a VDSL installation working correctly. Internet went down last night, and now is synching at 16Mbps/76Kbps.

The 16Mbps download sync rate is a poor indicator though, as we're getting extremely poor performance across the board when actually attempting to use the connection. And some things (such as running a Speedtest test) just don't work at all.

The frustrating thing is that this is a reasonably new development, which only started occurring after the second Chorus visit. Prior to that, we'd have performance degradations to approximately 6Mbps/3Mbps. Not ideal, but nowhere near as debilitating as what we now have.

One thing that may be a bit of a clue was that when we lost connectivity last night, it happened directly after the phone rang. Is it possible that the phone line can do that, now that we have a master splitter installed? It's a characteristic that our old ADSL modem used to consistently exhibit, but I never got around to getting it looked into.

Anyway, I have to dash. Need to ring the Chorus tech to tell him he's not done here yet....

make sure to note the voice line fault there, that is a clear indication of a fault to look into.

If you can constantly cause that to happen, you will be onto a winning example for when the techs show up.

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Any comments made are personal opinion and do not reflect directly on the position my current or past employers may have.

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