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Standard User Reentrant
(newbie) Sat 06-Sep-14 17:55:46
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FTTC very slow upload


[link to this post]
 
I'm some 900m from the cabinet and used to get around 28mbps downstream and 4mbps upstream; not great but acceptable.

But recently upstream has dropped to 800k. We've had a succession of Openreach engineers visit who can find no faults, and eventually blame crosstalk or REIN. Are there any clues in these stats?
https://www.flickr.com/photos/reentrant/14971278348/
Administrator MrSaffron
(staff) Sat 06-Sep-14 18:15:53
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Re: FTTC very slow upload


[re: Reentrant] [link to this post]
 
Other than not many bits present in U1 (second block of upload bins).

Attenuations looks relatively sensible. So may just be cross talk/rein issue but one only impacting a small block of frequencies because D1 looks sensible.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User Bald_Eagle1
(experienced) Sat 06-Sep-14 21:49:14
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Re: FTTC very slow upload


[re: Reentrant] [link to this post]
 
I'm 1100m from the cabinet & I have gradually lost around 10Mbps on my DS sync speeds (from around 30 Mbps to around 20 Mbps), definitely due to increased crosstalk.

However, I do still get around 4 Mbps US sync speed.

Did this US sync speed reduction hit suddenly or was it in noticeable stages?


Your connection's attenuation is better than mine, but my QLN is better than yours.
Has your QLN deteriorated suddenly?



Do you have any older snapshot stats for comparison against what your connection currently achieves?


Also, do you have any 24/7 Ongoing stats where you could go back & determine exactly when things started to go wrong?

If so, it may point to increased crosstalk, but I'd be rather surprised to see it hit your US sync speed so much as it usually hits DS sync speeds more significantly.


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Standard User Reentrant
(newbie) Sat 06-Sep-14 23:35:07
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Re: FTTC very slow upload


[re: Bald_Eagle1] [link to this post]
 
Everything had been fine up to a complete loss of service at the end of July. Openreach came out, couldn't find anything wrong physically but did a reset and reported sync back to 28mbs as before - I never thought to check upstream at the time and only noticed it when sharing some photos a week or so later. He said the service loss was due to "it going so slow for some reason it stopped altogether". The line passes all BT tests and the slow upstream sync also happens with just the BT test box connected directly to the incoming pair.

I only got a spare modem and unlocked that a few weeks ago after OR failed to find the cause so I don't have any stats from before the problem, unfortunately.

One OR engineer measured upstream at several points between the cabinet and me - it drops gradually from 10 at the cab to 4.5 mb/s at the last access point about 40 metres away. He did say they can see some very specific noise which is also affecting several other houses nearby but no-one else has complained so there's little they can do. Maybe the others haven't even notice slow upload. But he did say he's never seen a case of crosstalk or REIN only affecting upload, and this severely, while not affecting download at all.
Standard User WWWombat
(fountain of knowledge) Sun 07-Sep-14 01:29:27
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Re: FTTC very slow upload


[re: Reentrant] [link to this post]
 
Working backwards...

As others noted, the thing that looks very different is that the bit loading graph show the U1 band to be heavily under-utilised compared to the surrounding D1-D2.

This will be as a result of the SNR/tone being low in U1, perhaps by 15-20dB.

This appears to be because the QLN in U1 is particularly high - probably 20-25dBm higher than a lot of people. I just looked through all the people currently using "mydslwebstats", and a large proportion are showing -130 to -135dBm in the U1 band.

My QLN graph for U1 shows a U-shape (an upside-down version of your QLN), with a broad low at -136. while yours is n-shaped with a broad high of 110 dBm.

This ties in with your engineer's report that he can see noise in U1 that doesn't affect downstream.

So what generates noise at precisely the U1 frequencies, but doesn't stray into D1 or D2???

The obvious culprit would be a VDSL2 modem ... those know how to transmit on this frequency band, don't they? Perhaps one is broken somewhere. Perhaps one is just transmitting at the wrong level.

This suggests a path of going around the houses near that access point 40m away, and talking to them all. Find out if they have FTTC (perhaps checking if it was installed at the end of July), and if they have low upstream speeds. If they don't, you may have found the culprit. If they do, then you get them to generate a complaint so that Openreach will pay more attention.

If you find a culprit, you could check by asking them to turn their modem off for a while, and see if your SNR/tone graph improves.
Standard User MHC
(sensei) Sun 07-Sep-14 02:06:04
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Re: FTTC very slow upload


[re: WWWombat] [link to this post]
 
The upstream is totally affected from tone 950 to 1200 and partially from 870. Corresponds to about 3.7MHz (870), 4.2 MHz (950) and 5.2 MHz (1200). There does not appear to be anything affecting Downstream either side of the U1 block.

To me it suggests that any problem noise source is closer to the cabinet rather than at the OPs house.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User Bald_Eagle1
(experienced) Sun 07-Sep-14 09:41:24
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Re: FTTC very slow upload


[re: Reentrant] [link to this post]
 
If there is 4.5 Mbps available at the last access point, only 40m away (I assume that means the DP), yet drastically impaired at the bare wires of the incoming cable, that would suggest either the drop cable is 'damaged' or has a poor connection.

Alternatively, it could somehow be picking up severe interference within those 40m.

Did the engineer dismantle the master socket & clip his tester's cables to the bare wires or use an adapter plugged into the faceplate?

If it was the latter method, it is feasible that the faceplate itself is defective.



We had a couple of severe thunderstorms at the back end of July in my area (Oldham).

Following one of these thunderstorms, I still had a VDSL2 service, but the landline was completely dead.

I temporarily got around this by removing the faceplate & plugging an old ADSL microfilter directly into the master test socket.

That reinstated my landline service & my VDSL2 connection continued to operate as normal.


An engineer eventually visited & replaced the faceplate after testing everything at the bare incoming wires & explained that a number of users in my area had eperienced similar issues, with some losing landline, some losing VDSL2 & some losing both services.

He also confirmed that a small number of users also ended up with fried routers/modems & in one case the PC itself was fried.
It was assumed that those users must have been directly underneath the storm.


Do you have an old ADSL microfilter that you could try from the master socket, just to see if that makes any difference?

If it makes no difference, it would at least eliminate the SSFP as the culprit & more or less confirm the problem lies within the 40m of drop cable.


BTOR may be (should be) willing to replace or at least check the connections at each end of that cable.

My own drop cable was replaced a couple of years ago in an attempt to cure my intermittent disconnection & really low speed connection (it was actually also rerouted round the back of the house).

The issue on my connection ended up being a corroded connection between the underground cable & the drop wire that wasn't spotted when the drop cable was replaced.
Standard User WWWombat
(fountain of knowledge) Sun 07-Sep-14 11:34:58
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Re: FTTC very slow upload


[re: Bald_Eagle1] [link to this post]
 
What components exist on the backplate of the master?

That is, between the screw-connectors for the incoming twisted pair and the output pins of the test socket on the backplate.

If lightning could affect the SSFP, could it not also/instead affect the backplate?
Standard User WWWombat
(fountain of knowledge) Sun 07-Sep-14 11:36:13
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Re: FTTC very slow upload


[re: MHC] [link to this post]
 
The fact that the engineer can get 4.5Mbps only 40m away drives me to believe the problem is somewhere in that last 40m.

That is pretty much the original speed, and the 40m shouldn't make that much difference.
Standard User MHC
(sensei) Sun 07-Sep-14 11:39:39
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Re: FTTC very slow upload


[re: WWWombat] [link to this post]
 
But if the noise level was that high, close to the house, it would also affect the downstream signals which are already 40dB (or more) lower. The downstream graphs don't suggest a major localised noise issue.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
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