Help with varying ADSL line statistics and drops, please

P

PostmanPot

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Hi all

Been having an ongoing battle with ADSL line drops at a friend. They are 3.5 - 4.5km from the exchange in a sparsely populated, well treed area with lots of water and critters etc. (Constantia/Hout Bay). They run a 4Mbit line.

They use a D-Link DSL-2750 modem. Their ADSL line (separate line) would frequently drop 5+ times a day. I then asked Telkom to lower the sync rate to 3Mbit. The line stays up for longer now which is a good sign.

Last time I checked it was up for 2.5 days, a huge improvement. But the line stats seem to vary a lot.

Please take a look at these stats, taken this morning around 07h30:

Code: 
Downstream	Upstream
Line Coding(Trellis):	On 	On 
SNR Margin (dB):	238 	120 
Attenuation (dB):	75 	45 
Output Power (dBm):	-68 	8 
Attainable Rate (Kbps):	10848 	1164 
Rate (Kbps):	3072 	512 
D (interleaver depth):	1 	1 
Delay (msec):	0.13 	0.25

The line then dropped for 20 minutes at around 09h00, and these are the stats that followed as it came up:

Code: 
Downstream	Upstream
Line Coding(Trellis):	On 	On 
SNR Margin (dB):	[B]142 	80[/B] 
Attenuation (dB):	[B]155 	135[/B] 
Output Power (dBm):	[B]79 	123[/B] 
Attainable Rate (Kbps):	[B][U]8896[/U] 	[U]692[/U][/B] 
Rate (Kbps):	3072 	512 
D (interleaver depth):	1 	1 
Delay (msec):	0.13 	0.25

Is there anything we can draw from these statistics?

Thank you in advance for any help. :)

*edit*

Is it at all possible that the enabling of wifi could be causing the drops/erratic line stats (I think not)?
 
Last edited:
Update, 2 hours later. Only SNR Margin has gone up:

Code: 
Downstream	Upstream
Line Coding(Trellis):	On 	On 
SNR Margin (dB):	199 	80 
Attenuation (dB):	155 	135 
Output Power (dBm):	79 	123 
Attainable Rate (Kbps):	8896 	692 
Rate (Kbps):	3072 	512 
D (interleaver depth):	1 	1 
Delay (msec):	0.13 	0.25
 
Have you seen that thread where someone said that Telkom's guest account can be used to check ones line ? They said there are 2 tests one can make besides confirming or otherwise your ISP.
 
Something is definitely wrong there, because the upstream attenuation is supposed to be about half the value of the downstream one!
So you had excellent stats before 8:00, where your attenuation values were 7.5dB and 4.5dB respectively, which is low enough for a stable 10Mbps connection!

Try removing the ADSL filter and telephone(s) and see if your stats improve.

By the way, why are you connected at 3Mbps and not at like 10Mbps?
 
@PP: A downstream attenuation of 7.5dB (the router seems to be reporting in units of 0.1) would suggest a copper line length of roughly 500m (UMC?) so the line should be very stable. The attenuation should remain constant so it appears that there must be some type of line fault such as a a bad joint somewhere along the line. You could use this software to monitor the downstream attenuation over time. Retest the line after disconnecting all filters, surge protectors, telephones, fax machines etc. If there is no improvement then log a fault with Telkom.
http://vwlowen.co.uk/internet/files.htm
 
Pada said:
Something is definitely wrong there, because the upstream attenuation is supposed to be about half the value of the downstream one!
So you had excellent stats before 8:00, where your attenuation values were 7.5dB and 4.5dB respectively, which is low enough for a stable 10Mbps connection!

Try removing the ADSL filter and telephone(s) and see if your stats improve.

By the way, why are you connected at 3Mbps and not at like 10Mbps?
Click to expand...

Thank you Pada, I'm not sure if there is a filter as this is an ADSL line only, no telephone.

Around 6 months ago the line was replaced by Telkom to fix existing problems, but it seems that the new line hasn't helped. I think Telkom did their replacing up to the house, not sure if they worked on the property. I wonder if the problem lies on the property, as when I've logged faults, Telkom has mostly said the line is good on their side. I know their readings aren't always accurate. Once there was a fault at the DSLAM when they told us the line was fine. Should I investigate up till which point Telkom replaced copper?

The exchange is only 4Mbit enabled AFAIK - Houtbaai http://www.broadbandstats.co.za/exchange/WHBY.

When syncing at 4Mbit, the line would drop constantly. Since lowering to 3Mbit, it's been the first time that the line has been up for a couple of days without dropping.
 
Yotch said:
@PP: A downstream attenuation of 7.5dB (the router seems to be reporting in units of 0.1) would suggest a copper line length of roughly 500m (UMC?) so the line should be very stable. The attenuation should remain constant so it appears that there must be some type of line fault such as a a bad joint somewhere along the line. You could use this software to monitor the downstream attenuation over time. Retest the line after disconnecting all filters, surge protectors, telephones, fax machines etc. If there is no improvement then log a fault with Telkom.
http://vwlowen.co.uk/internet/files.htm
Click to expand...

Hi Yotch, and thank you, I will look into that app. :)
 
By the way guys, the modem has been tested elsewhere for 1.5 - 2 days on a few occasions, and never skips a beat.
 
@PP: Can you try to plug a line powered telephone directly on the line (without any filter). First check that there are no noticeable line noises etc. Leave the phone off hook and see whether the router will synchronise - my 10Mbps ADSL2+ line will still synchronise like this but I'm not sure about ADSL. You may find that the ADSL is more stable like this as the DC load from the telephone may improve the conduction through any bad joints. I often do this when my line gives trouble after heavy rains. The line quality might also improve if left like this for several days/weeks.
 
Yotch said:
@PP: Can you try to plug a line powered telephone directly on the line (without any filter). First check that there are no noticeable line noises etc. Leave the phone off hook and see whether the router will synchronise - my 10Mbps ADSL2+ line will still synchronise like this but I'm not sure about ADSL. You may find that the ADSL is more stable like this as the DC load from the telephone may improve the conduction through any bad joints. I often do this when my line gives trouble after heavy rains. The line quality might also improve if left like this for several days/weeks.
Click to expand...

Thanks, will look into this, not sure where to get a line powered telephone though (must be similar to the ones Telkom techies use). Funnily enough, since downsyncing to 3Mbit (and becoming more stable), the only time the line has dropped was in the morning on a day we had some morning rain. Could just be coincidence though.
 
Most cheap corded telephones should be line powered. The cordless phones usually have a separate power supply as they need more current than they are permitted to draw from the line. Any Telkom type telephone that doesn't have a separate power pack should be fine.
 
Morning all

Dropped at around 22h30 last night for a few minutes, here are the new stats as of 08h00:

Code: 
Downstream	Upstream
Line Coding(Trellis):	On 	On 
SNR Margin (dB):	266 	130 
Attenuation (dB):	75 	45 
Output Power (dBm):	-70 	11 
Attainable Rate (Kbps):	10784 	1180 
Rate (Kbps):	3072 	512 
D (interleaver depth):	1 	1 
Delay (msec):	0.13 	0.25

Seems almost the same as yesterday morning's good stats at 07h30 which Pada mentioned, also why the attainable rate has increased I guess.
 
Dropped 2 hours ago, just adding this again for my records:

Code: 
Downstream	Upstream
Line Coding(Trellis):	On 	On 
SNR Margin (dB):	197 	90 
Attenuation (dB):	155 	135 
Output Power (dBm):	52 	124 
Attainable Rate (Kbps):	10304 	708 
Rate (Kbps):	3072 	512 
D (interleaver depth):	1 	1 
Delay (msec):	0.13 	0.25
 
@PP: The line will usually drop when either of the noise margins drops below 6dB. Routerstats lite which should work with that D-Link router should give you a better idea of how the attenuation and noise margins are varying over time. If you leave it running you could also try to gently shake the dropdown wire or other sections of the aerial cable to see if there are any obvious bad connections. You could also check the terminal block where the phone line joins the house wiring as well as any Scotchlok connectors that you can reach by gently pulling on the wires. With a downstream attenuation of 7.5dB you should normally be able to achieve speeds of 20+Mbps on ADSL2+ or 40+Mbps on VDSL2+.
http://cubus-adsl.dk/elteknik/billedopslag/scotchlok.php
http://www.internode.on.net/residential/adsl_broadband/easy_broadband/performance/
Router frequency spectrum software (shows problematic frequencies etc.) ...
DMT for BCM6338/6348/6358 (might work with DSL-2750 BCM6328?)
http://dmt.mhilfe.de/
http://blog.orbmu2k.de/tools/orbmt-modem-tool-sidebar-gadget
 
Yotch said:
@PP: The line will usually drop when either of the noise margins drops below 6dB. Routerstats lite which should work with that D-Link router should give you a better idea of how the attenuation and noise margins are varying over time. If you leave it running you could also try to gently shake the dropdown wire or other sections of the aerial cable to see if there are any obvious bad connections. You could also check the terminal block where the phone line joins the house wiring as well as any Scotchlok connectors that you can reach by gently pulling on the wires. With a downstream attenuation of 7.5dB you should normally be able to achieve speeds of 20+Mbps on ADSL2+ or 40+Mbps on VDSL2+.
http://cubus-adsl.dk/elteknik/billedopslag/scotchlok.php
http://www.internode.on.net/residential/adsl_broadband/easy_broadband/performance/
Router frequency spectrum software (shows problematic frequencies etc.) ...
DMT for BCM6338/6348/6358 (might work with DSL-2750 BCM6328?)
http://dmt.mhilfe.de/
http://blog.orbmu2k.de/tools/orbmt-modem-tool-sidebar-gadget
Click to expand...

Thanks for the ongoing useful information.

The modem dropped several times yesterday. I've just logged in and it dropped 30 minutes ago. The wireless has also been disabled. I'm not sure if a user pressed the on/off button, or whether the modem disabled the wifi itself...

And the stats have changed again:

Code: 
Downstream	Upstream
Line Coding(Trellis):	On 	On 
SNR Margin (dB):	124 	90 
Attenuation (dB):	110 	80 
Output Power (dBm):	121 	123 
[B]Attainable Rate (Kbps):	5920 	724[/B] 
Rate (Kbps):	3072 	512 
D (interleaver depth):	1 	1 
Delay (msec):	0.13 	0.25
 
Hi there,
Just read through the posts.
Have you tried another router I know that you have tried the same router elsewhere and it was fine but if another router is stable maybe there is a problem with the router. Just want to eliminate another avenue of failure.
That said I think the problem will lie with Telkom and probably joints if they have replaced the cable recently.

Regards

Tim
 
The varying stats could well caused by the current spate of high temperatures, which continues to point to wiring. I'd suggest getting Telkom in in to do a full end to end test. Yes they will probably charge if the wiring is on the subs premises, but they are the only ones who can undertake a full end to end.
 
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