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Author Topic: Advice on diagnosing intermittent resyncs at half usual speed  (Read 2034 times)

flatspyder

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Hello, I've moved into a new home and trying to diagnose inconsistent broadband speed. I've tried searching on a bunch of things but after a couple of weeks decided to post and just ask for some advice :) Most of the time the line is synced around 56Mbit down but every now and then it resyncs in the 20s.

A little while ago the modem was connected with the following stats:

Code: [Select]
---------------------- ATU-R Info (hw: annex A, f/w: annex A/B/C) -----------
   Running Mode            :      17A       State                : SHOWTIME
   DS Actual Rate          : 29690000 bps   US Actual Rate       : 14145000 bps
   DS Attainable Rate      : 29615376 bps   US Attainable Rate   : 13817000 bps
   DS Path Mode            :        Fast    US Path Mode         :        Fast
   DS Interleave Depth     :        1       US Interleave Depth  :        1
   NE Current Attenuation  :       19 dB    Cur SNR Margin       :        5  dB
   DS actual PSD           :     7. 7 dB    US actual PSD        :     9. 2  dB
   NE CRC Count            :        0       FE CRC Count         :    39432
   NE ES Count             :        0       FE  ES Count         :    34190
   Xdsl Reset Times        :        0       Xdsl Link  Times     :       11
   ITU Version[0]          : b5004946       ITU Version[1]       : 544e0000
   VDSL Firmware Version   : 05-07-06-0D-01-07   [with Vectoring support]
   Power Management Mode   : DSL_G997_PMS_L0
   Test Mode               : DISABLE
  -------------------------------- ATU-C Info ---------------------------------
   Far Current Attenuation :       29 dB    Far SNR Margin       :        5  dB
   CO ITU Version[0]       : b5004244       CO ITU Version[1]    : 434da48c
   DSLAM CHIPSET VENDOR    : < BDCM >

I then rebooted the modem and it immediately resynced back in the 50s

Code: [Select]
---------------------- ATU-R Info (hw: annex A, f/w: annex A/B/C) -----------
   Running Mode            :      17A       State                : SHOWTIME
   DS Actual Rate          : 54985000 bps   US Actual Rate       : 12395000 bps
   DS Attainable Rate      : 54766804 bps   US Attainable Rate   : 12395000 bps
   DS Path Mode            :        Fast    US Path Mode         :        Fast
   DS Interleave Depth     :        1       US Interleave Depth  :        1
   NE Current Attenuation  :       19 dB    Cur SNR Margin       :        5  dB
   DS actual PSD           :     7. 8 dB    US actual PSD        :    12. 6  dB
   NE CRC Count            :        0       FE CRC Count         :    39432
   NE ES Count             :        0       FE  ES Count         :    34190
   Xdsl Reset Times        :        0       Xdsl Link  Times     :        1
   ITU Version[0]          : b5004946       ITU Version[1]       : 544e0000
   VDSL Firmware Version   : 05-07-06-0D-01-07   [with Vectoring support]
   Power Management Mode   : DSL_G997_PMS_L0
   Test Mode               : DISABLE
  -------------------------------- ATU-C Info ---------------------------------
   Far Current Attenuation :       29 dB    Far SNR Margin       :        6  dB
   CO ITU Version[0]       : b5004244       CO ITU Version[1]    : 434da48c
   DSLAM CHIPSET VENDOR    : < BDCM >

I have a Vigor 130 modem and have been trying to get DSLstats running, but so far no luck getting it to login. The stats above were taken from the Vigor's telnet prompt, so I am able to access it okay.

Any guidance for how to diagnose the issue?
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burakkucat

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Re: Advice on diagnosing intermittent resyncs at half usual speed
« Reply #1 on: May 01, 2017, 04:58:24 PM »

Welcome to the Kitz forum.  :)

On looking at the statistic snippets you have posted I immediately noted that you were using a Draytek modem/router and your Broadband service was provided as a G.993.2 over a metallic pathway (VDSL2). Hence I have moved this thread to a more appropriate location.

I always have great problems in fully understanding the information Draytek devices provide . . . and the Vigor 130 is no exception. That said, there certainly seems to be something peculiar happening with your circuit.

Unfortunately the Vigor 130 is not supported by DLSstats. 
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banger

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Re: Advice on diagnosing intermittent resyncs at half usual speed
« Reply #2 on: May 01, 2017, 08:59:33 PM »

Any noise on the telephone line? My first instinct would be a dodgy modem, is it an ISP modem? My second instinct is noise on the line when the modem is trying to sync.

Any idea why the re=syncs are happening, is it DLM, or noise burst or line fault?
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Tim
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https://www.thinkbroadband.com/speedtest/1502566996147131655

skyeci

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Re: Advice on diagnosing intermittent resyncs at half usual speed
« Reply #3 on: May 01, 2017, 11:53:47 PM »

Just an idea. Why not get hold of a broadcom modem so you gather some evidence via dslstats etc. If you have it running 24/7 hopefully you might catch it e.g. hg612 3b
Useful to give to your ISP or a visting engineer in the future.
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flatspyder

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Re: Advice on diagnosing intermittent resyncs at half usual speed
« Reply #4 on: May 02, 2017, 12:47:44 PM »

Thanks for the welcome. I'm pretty new to all this so forgive the questions while I get up to speed.

@banger I don't use the telephone phone for phone calls. What's the best way to test for noise, just plug in a telephone and listen? The modem is not from the ISP, I stopped using the old Zyxel one I received from them as it had a nasty memory leak and failed to persist login details so every now and then it would crash and require logging in to type the details in again. I don't know what is causing the resyncs, any tips for things to track that could help diagnose?

@skyci thanks, I'll see about setting up the old Zyxel router which looks supported by DSLStats.
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WWWombat

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Re: Advice on diagnosing intermittent resyncs at half usual speed
« Reply #5 on: May 02, 2017, 02:09:04 PM »

I don't know what is causing the resyncs, any tips for things to track that could help diagnose?

When, and how often, are the resyncs?

Resyncing in the course of a day is unusual for VDSL2, even when a line has problems. However, DLM can get involved because of issues with an increased error rate, or an increased rate of resyncs; any intervention by DLM then usually causes a resync too (usually between midnight and 8am) ... but that one obviously isn't the root cause of the issue, and is more a consequence.

A resync that isn't ordered by DLM, or triggered by a power cycle or physical disconnection, is then likely to be caused by noise on the phone line ... though this is noise in the VDSL2 spectrum, up to 17MHz, rather than noise you can hear. And, often, the biggest source of noise is the inadvertent crosstalk from your neighbours also running VDSL2 connections.

Over time, then, noise increases, SNRM levels drop, and the speed attained after a new resync will drop slightly. Sometimes you might drop just 1 or 2 Mbps, sometimes it could be 10Mbps for a particularly bad disturber. This is the usual picture for normal, working lines.

It is unusual for noise to decrease, and speeds to increase, unless one of your disturbers turns their modem off for a while. Someone who regularly turns their modem off each evening, and back on again in the morning, is creating havoc for some poor neighbouring line.

Your symptoms don't quite fit with that pattern - the drop of 25Mbps seems to be too much for one disturber. And your "Cur SNR margin" values of 5dB each time go against this too, but they are only limited snapshot figures.

Other causes can include EMI induced onto the line from sewage pumps, electric fences, etc.

To get a better picture of whether something like this is happening to your line, or whether you are the victim of high error rates, you really need to have the statistics being gathered into graphs, such as through DSLstats. Being able to visualise changes in SNRM, attainable speed, actual speed, FEC error rates, CRC error rates and ES counts all improves the advice you can be given.

Like @burakkucat, I find it hard to read the Draytek output, and find that most of the useful data is missing.

@banger I don't use the telephone phone for phone calls. What's the best way to test for noise, just plug in a telephone and listen?

Yes - if you are using a BTW voice line, then calling 17070 and selecting option 2 puts the line into a "quiet line test" mode, but essentially, you are using your ears to figure whether there is anything crackling, rustling or humming.

The theory is that if there's audible noise, then there is likely a line fault that creates noise that affects VDSL2 too.
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banger

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Re: Advice on diagnosing intermittent resyncs at half usual speed
« Reply #6 on: May 02, 2017, 07:15:32 PM »

Thanks for the welcome. I'm pretty new to all this so forgive the questions while I get up to speed.

@banger I don't use the telephone phone for phone calls. What's the best way to test for noise, just plug in a telephone and listen? The modem is not from the ISP, I stopped using the old Zyxel one I received from them as it had a nasty memory leak and failed to persist login details so every now and then it would crash and require logging in to type the details in again. I don't know what is causing the resyncs, any tips for things to track that could help diagnose?

@skyci thanks, I'll see about setting up the old Zyxel router which looks supported by DSLStats.

@flatspyder use a corded phone at the test socket, dial 17070 select 2 quiet line test and listen for about 5 minutes for any buzz or crackles on the line. Have a look on ebay for an HG612 dont pay over 15 quid as they are easy to unlock. You can then get broadcom stats.
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Tim
talktalkbusiness.net & freenetname
Asus RT-AC68U and ZyXEL VMG1312-B10A Bridge on 80 Meg TTB Fibre

https://www.thinkbroadband.com/speedtest/1502566996147131655

flatspyder

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Re: Advice on diagnosing intermittent resyncs at half usual speed
« Reply #7 on: May 03, 2017, 10:34:38 PM »

I have tested with a corded phone and there was no discernable noise on the line during the quiet test.

I've set up my old Zyxel 1312 which is supported by DSLStats. It's connecting to the internet fine but I'm currently unable to access the device itself from the network. It's in bridge mode to my router on a different subnet and something seems to be wrong with routing requests to it. Will try to diagnose so I can get DSLstats set up and look into buying an HG612.
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flatspyder

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Re: Advice on diagnosing intermittent resyncs at half usual speed
« Reply #8 on: May 07, 2017, 09:54:51 PM »

I finally have the Zyxel reporting data into DSLStats. Would be great to get any pointers what I should be looking into and collecting?

Incidentally since connecting the Zyxel it has synced at a higher speed (59.6/13.4) and not resynced in the last 3 days. Interleaving appears to have now been applied on the downstream.
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