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[finos]

Hello everyone.

Its my first time posting here , so if i make any mistakes rulewise , exuse me.
im a EE student from Greece , with a pasion for networks and .... a very unstable vdsl line  that my isp is unwilling to fix.


Im paying for up to 220/22 D/U mbit on a 35b profile, and my miniDislam cabin (Vendor: Broadcom) is located at a rather far 400m

when i firstly had this line installed at March of this year , knowing that i would not get my full speed , (synced at about 110/22) i was very satisfied knowing my loopLength
it was rock stable with my Rooted DGA4132 and i was satisfied.  The last 20 or so days the line is acting up almost to a unbareable state .

it would desync every half n hour or so , or it would drop down my rate (almost like doing SNR tweeking , but i know broadcom modems cannot do that...)
i remember its small "brother" the vunrelable TG789vac that it had the same behavour when the temperature got up , and trust me here in greece it does , i put a fan over the DGA
but it seemed to stabilize it but now even this doesnt seem to cut it ...

I have opened countless tickets on my isp but they close them because the linetype is "up too" (technicly i could get 54kbps and for them it would be fine..  )

im starting to "sniff" a  malfunctioning modem here , because this line was stable for over 4 months ...

my line stats are :

Code: [Select]

Line status
Online 30min
FEC errors (U/D)
(5173, 69202)
CRC errors (U/D)
(31, 124)
Power (dB) (U/D)
(9.9, 13.3)
SNR (dB) (U/D)
(10.5, 6.8)
Attenuation (dB) (U/D)
(6.7, 14.7)
Attainable speed (kbps) (U/D)
(27476, 83083)
Synchronized speed (kbps) (U/D)
(22000, 85367)

any sugestions before i step down to the terible (both in speed & in value ) 110/11 packet?

[burakkucat]

Welcome to the kitz forum. 

Im paying for up to 220/22 D/U mbit on a 35b profile, and my miniDislam cabin (Vendor: Broadcom) is located at a rather far 400m

when i firstly had this line installed at March of this year , knowing that i would not get my full speed , (synced at about 110/22) i was very satisfied knowing my loopLength

In the UK, VDSL2 circuits are provisioned on Profile 17a and so that is from where our collective knowledge originates.

Without looking up the typical characteristics of a Profile 35b circuit and doing some calculations, a synchronisation speed in the range 110/20 Mbps to 120/30 Mbps (DS/US) looks about right for a metallic pathway of around 400 metres. So perhaps it might be sensible, cost-wise, to downgrade the service?

As for a failing CPE, let's see what other members think.

[Weaver]

Welcome Finos! Can you swap out the modem ?  What is the temperature just now? Has it been unusually hot? You say putting a fan over the modem didn’t help. Was that outside the casing or internal, and over the processor? I would also swap out the PSU in case this is failing, as it’s a cheap measure.

[meritez]

I'd open the casing and put heatsinks on the cpu, modem etc chips

[Alex Atkin UK]

I'd agree in swapping out the PSU first, those things tend to cook the capacitors over time and this will only be worse in hotter climates.

Of course the capacitors in the router itself can also go bad.

Totally unscientific guess, but I'd say 9/10 those are the problem rather than the router itself overheating.

[finos]

Well , i made a intresting discovery .....

this is a photo of my rack that i have at home ,
you can (barely ) see the DGA on the right , with the fan on top . the white CPE on the left is a Sercom Speedport Plus that my ISP uses to provide me with phone service (some day id have to swap it out with a Cisco ATA..)

The Sff pc down bellow is my Pfsense router , with the problematic SMPS, i tried shuting it down for the night  , and my line , even though didnt go back to its "normal" sync of 90/20 it was stable with no deSyncs ...

Welcome Finos! Can you swap out the modem ?  What is the temperature just now? Has it been unusually hot? You say putting a fan over the modem didn’t help. Was that outside the casing or internal, and over the processor? I would also swap out the PSU in case this is failing, as it’s a cheap measure.

i have a new sfx psu for the pc on order , plus a Draytek 2765 they should arrive by the time i will be on site , the temperatures were 34-37 during the day and the fan ,as you see from the photo is over the DGA.

I'd agree in swapping out the PSU first, those things tend to cook the capacitors over time and this will only be worse in hotter climates.
Of course the capacitors in the router itself can also go bad.
Totally unscientific guess, but I'd say 9/10 those are the problem rather than the router itself overheating.

when i opened the DGA to root it its caps seemed fine , ill have with me a new psu for it .

Welcome to the kitz forum. 

In the UK, VDSL2 circuits are provisioned on Profile 17a and so that is from where our collective knowledge originates.
Without looking up the typical characteristics of a Profile 35b circuit and doing some calculations, a synchronisation speed in the range 110/20 Mbps to 120/30 Mbps (DS/US) looks about right for a metallic pathway of around 400 metres. So perhaps it might be sensible, cost-wise, to downgrade the service?
As for a failing CPE, let's see what other members think.

My isp had a limited offer for a free upgrade from the 110/11  service to the 220/22 service with the price of the 110 , i needed the incereased upStream bandwidth and the fact that i wouldnt pay more made the offer more apealing .But it would be a bummer if i had to trade the stablility of the line ...

[Alex Atkin UK]

Worth noting, caps don't always look bad, it depends if they go bad leaking or dry out slowly leaving no evidence.

Its wise however to look into all other options before breaking out the soldering iron.  Generally I'd be wanting to keep the modem as far away from other equipment as possible to reduce the chance of them interfering on the DSL side.  The shorter the phone line inside the house, the less chance of interference from inside the home.

[finos]

So, I'm back again after running some tests

Installing the draytek modem on the line, performing snr tweeking in hopes that giving up some speed I'd get some stability did not go well.  My dislam is a Broadcom joby and the draytek is infinion, the stability was even worse than before.

I checked at the bit bins diagrams, looks like now the line operates with  using fewer bins, the us1 band is almost cut off  snr and qln are all over the place    I'll upload tomorrow the before and after...
I re-checked my internal wiring (sheild foiled cat6a cable that runs from the pole to my rack) measured at the isp handoff point and at my rack, I lose only 0.2mbit.. It was not my internal wiring.

Lastly, I contacted a local field isp tech, who told me that there was a accident down the road, almost in the half distance between me and my dislam cabin who a careless public works worker( with his excavator I suppose) chopped off half of my towns dsl lines .. I guess the repair of the wires wasn't done very "up-to - spec"  and that's why my problem was that exaggerated.

With that data I think my only pathyis downgrading my service...what do you guys think?

[Weaver]

I was going to say… Some people me included are not huge fans of Draytek modems because they use Infineon chipsets, as you say. I would have recommended a Broadcom-based modem to match your DSLAM. I think that here modem-choice is perhaps everything? Also you will need to keep your downstream SNRM up so as not to get too many uncorrected errors, and not push it too much. Sync rate isn’t everything, not if you’re getting so many errors that you can't successfully run UDP-based protocols and even TCP actually goes slower because of all the retransmissions and speed-backoffs resulting from corrupt packet loss. I made that mistake, so now I make sure that I have zero CRC errors and zero ES (errored seconds).

Another question : Does your DSLAM have G.INP?

As for going down to the slower speed service, no I wouldn’t. Didn’t you say that the faster service has better upstream ?

[Alex Atkin UK]

Also as it was a free upgrade and downgrading probably isn't going to make it any more stable.

[finos]

I was going to say… Some people me included are not huge fans of Draytek modems because they use Infineon chipsets, as you say. I would have recommended a Broadcom-based modem to match your DSLAM. I think that here modem-choice is perhaps everything? Also you will need to keep your downstream SNRM up so as not to get too many uncorrected errors, and not push it too much. Sync rate isn’t everything, not if you’re getting so many errors that you can't successfully run UDP-based protocols and even TCP actually goes slower because of all the retransmissions and speed-backoffs resulting from corrupt packet loss. I made that mistake, so now I make sure that I have zero CRC errors and zero ES (errored seconds).

Another question : Does your DSLAM have G.INP?

As for going down to the slower speed service, no I wouldn’t. Didn’t you say that the faster service has better upstream ?

the Draytek turned out to not work for me at all . no amount of SNR tweeks it just wouldnt sync relibly .

My dislam uses G.IMP , and somthing werid i noticed ,Both modems reported "VDSL mode : Fast" but when i contacted my ISP to have fastPath removed and use a interleved profile , they said i already was on a interleaved profile .

now , here are some historical data from my line , that i keep on my grafana dashboard( perhaps i should make a post about my monitoring software... )
You can see that for over a month the line was stable , and whats happening now..

[Weaver]

That really looks like a fault to me. I am an expert on faults not on VDSL2.

[finos]

A update on my situation ,
the feild techs have now virtualy downgraded me to the 110/11 service ( meaning that my contract is still at the 200 service , but for testing they manualy set the dislam is at the 110 profile ,
that also comes with 17a , the line is rock solid  and i basicly have my old line , minus a cupple of megbit on the down path...

Also as it was a free upgrade and downgrading probably isn't going to make it any more stable.

I will try to contact the field engineer , to see  if he can find me a "cleaner" pair coming from the Dislam ,  probably due to the cut I had on that cable , it was re-joint poorly and thus I experienced the issues , I believe this because the hlog and qln graphs suggest cable fault ( if I can interpret them correctly)

[neil]

t

now , here are some historical data from my line , that i keep on my grafana dashboard( perhaps i should make a post about my monitoring software... )
You can see that for over a month the line was stable , and whats happening now..

Please do a detailed post about it. Software, hardware and all the tweaking.

[finos]

First and foremost , we have some good news, we are finaly up to my previous line while being stable 

i was contacted by one of the Feild techs who was willing to put the efford to find a "clean" pair from my dislam to my house .

now im back at 89/22 and  i will be monitoring it for stability in the days coming.

Please do a detailed post about it. Software, hardware and all the tweaking.

i will make a detailed post in the following days for sure ! But i m kinda buzzy now