Demystifying VDSL DLM

Forums › Spark New Zealand (including Skinny and BigPipe) › Demystifying VDSL DLM

dclegg

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#198548 13-Jul-2016 14:17

Yesterday I upgraded my Spark ADSL2 connection to VDSL. I was initally excited to see that my 15/1 Mbps connection was now performing at 50/10 Mbps. I woke up this morning to find it had changed to 5/2 Mbps.

A bit of digging found out that this was due to DLM. I read a few references around, including this excellent one here. However, none of it really helped to temper my expectations as to where I'll actually end up.

Is it common for the DLM process to initially try both ends of the sync spectrum before settling on a profile to use? All the Chorus installer told me was that I was currently synching at 50Mbps, but that'll improve over the next few days. He made no mention of speed dropping to 10% of that.

Or is it quite possible that my current low sync speed is a closer indication to what Chorus deems is appropriate for my connection?

For reference, here are my modem stats (using the Spark supplied Huawei HG630b):-

DSL synchronization status Up
DSL up time 06:25:09

Line standard VDSL2
Downstream line rate (kbit/s) 5720
Upstream line rate (kbit/s) 3529
Downstream SNR (dB) 37.7
Upstream SNR (dB) 24
Downstream line attenuation (dB) 11.9
Upstream line attenuation (dB) 6
Downstream output power (dBmV) 13.1
Upstream output power (dBmV) -3.7
Downstream CRC 0
Upstream CRC 7
Downstream FEC 37
Upstream FEC 665

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#1590995 13-Jul-2016 14:17

Hello... Our robot found some keywords in your post, so here is an automated reply with some important things to note regarding broadband speeds.

If you are posting regarding DSL speeds please check that

you have reset your modem and router
your PC (or other PCs in your LAN) is not downloading large files when you are testing - you are not being throttled by your ISP due to going over the monthly cap
your tests are always done on an ethernet connection to the router - do not use wireless for testing
you read this topic and follow the instructions there.

Make sure you provide information for other users to help you. If you have not already done it, please EDIT your post and add this now:

Your ISP and plan
Type of connection (ADSL, ADSL2, VDSL)
Your modem DSL stats (do not worry about posting Speedtest, we need sync rate, attenuation and noise margin)
Your general location (or street)
If you are rural or urban
If you know your connection is to an exchange, cabinet or conklin
If your connection is to a ULL or wholesale service
If you have done an isolation test as per the link above

Most of the problems with speed are likely to be related to internal wiring issues. Read this discussion to find out more about this. Your ISP is not intentionally slowing you down today (unless you are on a managed plan). Also if this is the school holidays it's likely you will notice slower than usual speed due to more users online.

A master splitter is required for VDSL2 and in most cases will improve speeds on DSL connections. Regular disconnections can be a monitored alarm or a set top box trying to connect. If there's an alarm connected to your line even if you don't have an alarm contract it may still try to connect so it's worth checking.

I recommend you read these two blog posts:

I am the Geekzone Robot and I am here to help. I am from the Internet. I do not interact. Do not expect other replies from me.

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hio77

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#1591013 13-Jul-2016 14:28

Your snr is way out of spec, That is your issue. in this case, Nothing todo with DLM at all really.

Normally i would not recommend it, but in this case, cycle your modem.

Was there a Master filter installed? Internal wiring is a likely cause of this.

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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.

dclegg

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#1591015 13-Jul-2016 14:31

hio77:

Your snr is way out of spec, That is your issue. in this case, Nothing todo with DLM at all really.

Normally i would not recommend it, but in this case, cycle your modem.

Was there a Master filter installed? Internal wiring is a likely cause of this.

Modem was cycled this morning. It is my understanding that cycling the modem should be avoided if at all possible during the first few days that the DLM is operating.

Master filter was installed yesterday, when VDSL was connected.

House is only 14 years old. It is an ex-leaky home, which has just had its external cladding replaced.

hio77

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#1591016 13-Jul-2016 14:36

dclegg:

hio77:

Your snr is way out of spec, That is your issue. in this case, Nothing todo with DLM at all really.

Normally i would not recommend it, but in this case, cycle your modem.

Was there a Master filter installed? Internal wiring is a likely cause of this.

Modem was cycled this morning. It is my understanding that cycling the modem should be avoided if at all possible during the first few days that the DLM is operating.

Master filter was installed yesterday, when VDSL was connected.

House is only 14 years old. It is an ex-leaky home, which has just had its external cladding replaced.

Yes that is exactly the case, as i said Normally i would not recommend it.

Pull it down to extact stats for you.

Profile your on is most likely a 9dB 8b bandplan.

Your currently connected at 38/24 snr rather than 9dB. it riding that high is an indicator of something going wrong.

Often that happens when there is quite a change to the network, say a power outage line fault, water in the lines etc.. An easy way to drop back down to the 9dB is to resync, then look at the damage.

A single cycle will be okay for VDSL, are you saying you have already tried cycling it since this speed drop started however?

#include <std_disclaimer>

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

dclegg

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#1591020 13-Jul-2016 14:39

hio77:

Yes that is exactly the case, as i said Normally i would not recommend it.

Pull it down to extact stats for you.

Profile your on is most likely a 9dB 8b bandplan.

Your currently connected at 38/24 snr rather than 9dB. it riding that high is an indicator of something going wrong.

Often that happens when there is quite a change to the network, say a power outage line fault, water in the lines etc.. An easy way to drop back down to the 9dB is to resync, then look at the damage.

A single cycle will be okay for VDSL, are you saying you have already tried cycling it since this speed drop started however?

I rebooted the modem at around 8AM this morning. Haven't done so since.

hio77

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#1591027 13-Jul-2016 14:50

dclegg:

I rebooted the modem at around 8AM this morning. Haven't done so since.

Has it been since that reboot that your line got unhappy or Before it?

#include <std_disclaimer>

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

dclegg

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#1591029 13-Jul-2016 14:54

hio77:

Has it been since that reboot that your line got unhappy or Before it?

Before. I rebooted in an attempt to fix the slow speeds. I didn't have actual modem sync stats at that time, nor do I have them from yesterday unfortunately.

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hio77

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#1591031 13-Jul-2016 14:56

dclegg:

hio77:

Has it been since that reboot that your line got unhappy or Before it?

Before. I rebooted in an attempt to fix the slow speeds. I didn't have actual modem sync stats at that time, nor do I have them from yesterday unfortunately.

Ight okay, so we are at the point of, something has gone wrong and you have rebooted to fix that possible casuse.

At this point personally ild be calling the isp and requesting a 24 hour line test to gain more figures on how things are looking.

Due to being within your 10 days, it could be hard to get that response out. But obviously riding up into the 30dBs is not right.

#include <std_disclaimer>

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

dclegg

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#1591033 13-Jul-2016 14:58

hio77:

Ight okay, so we are at the point of, something has gone wrong and you have rebooted to fix that possible casuse.

At this point personally ild be calling the isp and requesting a 24 hour line test to gain more figures on how things are looking.

Due to being within your 10 days, it could be hard to get that response out. But obviously riding up into the 30dBs is not right.

Spark has already informed me to keep an eye on things over the next few days, and report back if it stays < 15Mbps

Jase2985

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#1592098 13-Jul-2016 17:01

wiggle some wires and see if anything changes :) just don't tell your isp you did that if the connection stops working

dclegg

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#1592967 15-Jul-2016 10:28

So this DLM thing has me totally stumped.

It's my understanding that it's meant to analyse your line quite aggressively over the first 10 days of a new VDSL connection, and make nightly changes to optimise. These were my stats for the last three mornings:-

I asked Chorus via Twitter whether this was normal, considering I started off with 50Mbps/10Mbps. They asked for my details, and got this reply

Thanks David, we've just checked your line out for you. Can you please run another speed test?

After which, my router stats now look like this :-

So I'm not entirely sure what action Chorus took, but why wasn't the DLM process able to make overnight profile changes to slowly move me up to this point? Why did it keep me on a very slow profile?