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[rjpreston]

Hi all,

After months of reliable and stable connection at around 32Mb down and 7.9Mb upload, in the past week or so the upload has halved in speed. Before i prepare to engage the ISP (BT) please could someone offer advise on what might be happening to the upload connection?

The phone connection is fine and the line is quiet (no crackles hisses or pops etc). The download speed seems unaffected and is reasonable given we are quite a distance from the exchange (about 825m). Line runs to exchange underground and on overhead wires. VDSL modem is a Zyxel VMG1312-B10A and router is Asus RT-AC68U running Merlin fw.

DSLstats charts attached covering 15 Feb to today
* Problem had been happening for a week or so before the weekend of 15/16 (which was the weekend Storm Dennis). Upstream SNR is all over the place. Previously,the  "normal" was 6dB
* I manually rebooted on afternoon of Sun 16th. Upstream returned to 8Mb and stayed like that all week
* Wet & windy weather last weekend caused the upstream speed to slow again. I switched the modem off overnight. it rebooted back to 6dB and 8Mb speed upstream.
* Yesterday it went again - SNR right back up to 13dB and upstream speed plummeted.

Downstream speed seems completely unaffect which is what is flummoxing me. Cant understand how up is impacted by some sort of noise and errors whilst the downstream is completely fine!

[j0hn]

Looks like some kind of intermittent noise causing the upstream SNRM to drop, sometimes as much as 10-12dB.

When the line is at 6dB the large drop in SNRM causes a resync.
If the noise is still present during the resync then the line comes back up with a high SNRM and subsequently a lower sync.

If the above, a resync should return the line to normal until the noise returns.

Try another modem if you have 1 to rule that out.

Distance to the exchange is irrelevant with FTTC unless your cabinet is directly outside it.

[rjpreston]

Thanks J0hn

I have an HG612 which i can try. Good suggestion, and i will try it if nothing improves soon.

Yes, cab is right outside the exchange. But i think the download speed is pretty much spot on for the distance.)

The upstream speed was previously solid 7.8-8.0Mbps until two weeks ago - and there is some evidence that the interference is weather-related. I will walk the route to see if there is any obvious signs of wind-damage / leaning trees etc.

i am confused why it would only affect the upstream though, and leave the downstream completely unaffected?

[Alex Atkin UK]

If its interference then its not totally unusual that it might only impact specific frequencies that just happen to be upstream.  Why this is worse during different weather is curious, but RF does propagate differently depending on the weather/atmospherics.

[rjpreston]

I've walked along the route to the cabinet (i live in a rural arfea so pretty certain which way the BT cables are routed. I'm now pretty certain  they are 100% underground. So maybe not wind affecting but could well be rainwater.

Bit loading chart attached shows lots of frequencies in the upstream range that are v noisy.

Guess I'll have to a) try my HG612 modem to check whether it is my Zyxel going bad. Failing that b) ring BT

One other thing confuses me. The DSLStats stats page shows the upstream modem power to be very low (5.4dBm) whereas the Dowmstream is 12.9dBm. seems counter-intutive to me - if there a noisy line youd think the modem would increase the power to 'blast' through it (though i admit i speak as a mechanical engineer by degree, so not well versed in communications engineering principles!!)

[mofa2020]

I've walked along the route to the cabinet (i live in a rural arfea so pretty certain which way the BT cables are routed. I'm now pretty certain  they are 100% underground. So maybe not wind affecting but could well be rainwater.

do you know if there is any phone lines manhole on the route you walked? or is there any power equipment that are on that path that may be located near the route? something like transformer or so could be related to earthing!!

and yes on noisy lines power would be higher than quieter one or even on same line depending on interference affecting downstream/upstream.
 
I had an issue with my line before FTTC but it was on the download side when it rains heavily signal deteriorate quickly.

[Alex Atkin UK]

and yes on noisy lines power would be higher than quieter one or even on same line depending on interference affecting downstream/upstream.

I was going to say I think that power level IS already blasting.

My bad line pushes 5.2dBm whereas my good line only needs 3.8dBm.

[mofa2020]

I was going to say I think that power level IS already blasting.

My bad lne pushes 5.2dBm whereas my good line only needs 3.8dBm.

Mine is ~4db usually.

[rjpreston]

do you know if there is any phone lines manhole on the route you walked? or is there any power equipment that are on that path that may be located near the route? something like transformer or so could be related to earthing!!

Numerous BT "manhole" covers along the route. probably 4 in our street and then two-three more along the road to the exchange. No power transformers.

[rjpreston]

Mine is ~4db usually.

I think I've seen it higher still!

Next step will be to try the other modem and see if it makes a difference. I used to use it (HG612) but swapped to the Zyxel as it upp'ed the speed by a good 15-20%. But he HG612 was still better than all the BT-supplied modem-routers i have.

[mofa2020]

probably water going inside and causing problems, it is weird that only the upload affected but I had this experience before on download found no explanation and after fttc my line got connected directly to the cabinet and they canceled that manhole my line was previously connected through.