VDSL slow upstream

[#1]

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@chroma2000 wrote:

Why is upstream more susceptible to interference than downstream?

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The DSL signal is encoded using a large number of separate frequency bands - each band encodes a part of the data, so the total bandwidth is the bandwidth of all the separate frequencies added together.

Some frequency bands are allocated for upload, and the remainder for download. The lowest frequencies - the audible part of the spectrum - are reserved for the audio phone calls. The next set of frequencies are upload, and the remainder download. The micro-filter keeps the audio phone frequencies and the DSL frequencies from interfering.

There are two reasons upload is more susceptible than download:

1) there are many more frequency bands allocated for download - around 10 times as many - which is why the maximum download rate is faster than the maximum upload rate

2) the upload frequencies just happen to be those where "noisy" electrical and electronic equipment make most noise.

When there is noise on a particular frequency band it reduces the throughput on that frequency - or even blocks it altogether. As there are far fewer upload frequencies than download available, losing one makes a bigger percentage difference to the upload speed than losing one of the download frequencies does to the download speed. Noise on several bands has the sort of effect you are seeing.

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More realistically why cannot the Openreach equipment better determine the optimum upstream speed, 

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That's exactly what it is doing - it is finding the optimum speed that actually works reliably.  Transmitting too fast on a noisy line results in many errors, which reduces the speed and increases latency.

Plusnet may be able to (get OR to) investigate this, but unlike download speed there is no minimum guaranteed upload speed.

[#2]

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@K5Hall wrote:

Now I'm no expert but I am a semi-retired Electronics Engineer but as far as I am aware nothing my side of the router can affect the DSL line speed and that is down to them setting it - please someone confirm as to whether I am right or wrong.

Your internal network shouldn't have any effect on the DSL speed. Your local environment could if there is something creating electrical interference.

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Also I don't believe that the DLM will borrow speed from the DSL upstream to deliver a faster download (their side determine up and down speed) - please someone confirm as to whether I am right or wrong.

I don't believe that can happen.

I also believe that downloading huge files will not affect the DSL Up or Down speeds as the file is limited to the down speed and will take the required length of time - please someone confirm as to whether I am right or wrong.

A large download will require a lot of ACKs to be sent upstream - in cases where there is a limited upstream data rate it can reduce the achieved download rate. However, it won't affect the DSL link speeds. 

[#3]

All of the Slow speeds are usually preceded by Upstream variation in SNR and DSL drop-outs.

All of this is being dealt with by Question #237672755 - hopefully.

However Sixth Openreach engineer out after more drop-outs.

Came Wednesday morning 8th Nov and performed many tests. He had some strange readings in that initial test showed 50M down and 3M Up. However after performing a second test he got 29M Down and 15M Up. He couldn't understand that and said that it was "all over the place". Went to cabinet and checked there. Came back and checked internal wiring from Router cable through the filter and Master socket and stated that there was no problems with the cable and that this was a strange problem.

He left and the signal had come back up to 54M Down and 14M Up.

However, on Saturday 12th Nov there were 6 drop-outs and speed was eventually 52M Down and 10M Up.

Also the SNR margin on the Upstream seems to be affected by telephone calls depending on the time of day and sometimes calls have caused the DSL to drop-out.

Results for Saturday and Monday - involving 3 phone calls - 2 received and 1 made are in the attached document.

Anybody have any clue as to why this could be happening? Faulty filter between POTS and DSLAM? Problem with POTs or DSLAM?

Note : Router/Modems have been changed without making any difference.

[#4]

Question #237672755 - more data to help sort out the issue.

Document contains plots for Monday 13th Nov showing Effects of Landline calls during the day. Note morning had no issues while 2 others later on in the day caused an issue - only on the Upstream SNR, Downstream hardly affected.

Tuesday 14th Nov showing effects of landline calls on SNR - again only Upstream affected - note additional period of SNR variation. Yet again hardly any effect on Downstream.

Wednesday 15th Nov - showing landline call at 11am but no further calls during the day. Note significant SNR variation on U[stream causing DSL to drop and Upstream DSL sync dropping significantly from 10,033kbps to 1,033kbps and SNR increasing to 19dB. Yet again hardly any effect on the Downstream SNR.

Interesting to note that the Downstream increased after the drop out from 52,333kbps to 53,742kbps.

Why is it that the Downstream recovers but the Upstream does not?? Is it to do with interference on the lower DSL frequency bands that are used by the VDSL signal that are closer to the audio phone range???

[#5]

I find my downstream snr is generally quite steady at 56Mbs/6.0db. The upstream snr has random periods of instability, although not for the last 6 days. Possibly the weather has an influence. At present my upstream is syncing at a steady 2Mbs/14db snr.

I did a test ringing the landline and it actually improved the downstream snr by 0.5db and the upstream snr by 1.0db. 

[#6]

Thanks for your comments.

However, if I received that I would be a little disappointed.

My issue is the drop outs that keep causing the Upstream to drop - the drop outs usually do nothing to the Downstream.

My contract suggests:

          Download : 39 -44Mbps at peak times, Upload :11 -  13Mbps at peak times.

          Max Download 45Mbps, Max Upload 13Mbps and Minimum Upload 11mbps at off-peak

These seem to agree with the BT Availability Checker which states that from my cabinet VDSL Range B (Impacted) Down 55 to 38.6Mbps, Up 15.7 to 8.8Mbps. BT Openreach engineers seem to agree as they suggest I should be getting 45 to 50 Down and around 12 Up. So having a drop out that causes the Up to drop to 1Mbps (recently  a drop out caused it to go below to 0.156Mbps) is not acceptable or fit for purpose especially for meetings.

As you can see from the Sat_11_Nov.doc after the last engineer the line was good at Down 54.395Mbps and Up 14.698Mbps and it was stable and recovered to this from a drop out but the noise issue on Saturday obviously caused the DLM some issue. This is intermittent noise which the DLM should take care of and not just keep dropping the Upstream speed.

[#7]

It is disappointing!

I know my line can support 15Mbs upload on a good day. Unfortunately there is no guaranteed minimum upload in the terms and conditions so it looks like I have to put up with a steady 2MBs until full fibre. On the plus side despite a few bouts of interference my connection hasn't dropped for 7 days.

[#8]

Of course as soon as I posted the previous reply the line went down!

Now the upload speed has gone up to 9Mbs so I expect a cycle of disconnections again until it gets down to 2Mbs.

[#9]

I know they keep saying "there is no guaranteed upload speed". However, that is ***** as you need an upload to be able to get the download. There will always be some upload during you download.

My contract sent in email states:

"Here are some additional off-peak speed estimates for you line

Maximum download speed : 45Mb, Maximum upload speed: 13Mb, Minimum upload speed: 11Mb"

They have provided a Minimum in there estimates and so anything falling significantly lower than this like 1Mb is not the service they should be providing.

Note the attached Wed_15_Nov.doc giving interesting plots for Wednesday 15th Nov to Sun 19th Nov.

This shows the disturbances to the SNR due to landline calls and that even after the call there is erroneous noise - which should not be there in that amount - which caused the DSL to drop on Wednesday 15th Nov and the upload to drop 1Mb funny that the download didn't decrease. The upload then remained at this lower speed of 1Mb through Friday, Saturday and Sunday morning when I disconnected the router from the Master socket for greater than 15min (DLM period?).

The upload speed then went back to normal of 14Mb.

It is strange the the DLM can react to noise and reduce the speed to enable a "stable upload" for a small period of noise yet when the line has bee stable for over 3 days with the SNR of 18db (12dB greater than the expected usual of 6dB - 12 db is a margin of 2^4 or 16 times greater signal to noise) that it does not just increase the speed slightly and keep a monitor. So effectively the DLM is doing a half-[-Censored-] job i.e. it will only keep reducing the speed and not try to increase the speed if the line has quietened down. If designed correctly should also be pro-active and increase the speed to achieve the best speed for a given SNR limit.

Anyway, saying all that, today the DSL dropped 6 times and am back to upload of 2.4Mb with huge SNR of 16.9dB whilst yet again the download is 53.7Mb with an SNR of 6.3dB.

[#10]

Personally I would push them on the minimum upload speed as specified in that e-mail. I would argue that that was promised and you'll not be happy with anything much less.

They will probably argue that it was an "estimate" only, and that there is no guaranteed minimum upload speed in the contract. I would argue that any reasonable person would expect to get close to the estimated speed.

In situations like this a friend used to say "it is the squeaky wheel that gets the oil" - so I'd make sure Plusnet hear the squeak... 

[#11]

As stated previously.

Reset the line on Sunday 19th Nov by disconnecting from Master Socket for >15mins.

Great speed in BOTH directions.

Monday 20th SNR varied followed by 6 DSL drops eventually resulting in GOOD Down (53.7Mbps) but LOW up (2.2Mbps) sync and again the correct SNR for Up of 6.0dB but HUGE SNR for Down of 17dB.

See attached Sun_19_Nov.doc for plots of Up SNR, Down SNR and Up sync for the Sunday with the reset and then the events of Monday.

Yet again only the Up SNR seems to be affected.

[#12]

It does look suspicious that phone calls can trigger the change in SNR - are you using a BT filtered faceplate or a dangly filter?

Has an engineer replaced the master socket at all?  I'm wondering whether the line always tests good when an engineer tests it is simply because nobody is using the telephone at those times. If cross-talk from the telephone is the cause, it could happen at either end, but is much more likely to be at your end.

[#13]

Phone calls can cause a change in the Upstream SNR but sometimes there is no change. It seems slightly random.

I've had phone calls from Plusnet that have caused the line to drop and some that have caused no disturbance at all.

BT Master Socket and filter plate have been changed at the second engineer visit (he's the one that suggested the upstream issue would more likely suggest a problem at the cabinet end) and the last engineer checked through from the actual cable used by the router through the socket and gave them a clean bill of health.

So whatever connections/filters ports they haven't changed so far should be the ones that are more likely to be suspect.