Line speed dropped by system

[prasadm]

I have not started a new topic because the issue I have seems to be a recurrence of a previous problem. If you think I should, please can you let me know, and I can do that. Thanks

This seems to be a recurring issue now, after 4 months of stable speeds at 41+ Mbps, suddenly the speed dropped to 37.13 again, without doing anything at my end. In fact if the past data is looked at, after every 14 day restarts, the speed was consistently improving although by a very small margin, but trend was upwards. Here are the values which I recorded (since that time up until yesterday.

41.415
41.648
41.855
41.648
41.338
41.984
I have done the standard checks, quiet line test - done and no noise. Have no spurs on the telephone line, and router is connected at the master socket. Seems like something at the BT side. If it is a temporary test or something BT is doing I would expect them to let us know, but have heard nothing. But this seems a bit odd to suddenly drop speed by 5 MB, wonder if I complain where should I do this. (broadband or line fault) ? I have also done a quick check of the maximum data rate which I have seen in the past is a very dynamic value, for approx 4 Hours, and cant see any major issue there either from previous. So why would just the connected speed drop ?

  Maximum downlink data rate & Noise Margin (4 hours this morning)

[prasadm]

I have the speeds monitored over last 2 days and I am unable to find anything that would cause a problem with the D/L speed that it has to drop 5 Mbps. The max rate on my line remains where it has been seen in the past but the NM has increased and actual connected speed dropped. Is this a mechanism to drop the speed to fit within the BT database which has dropped and shows downstream line rate maximum of 40 , when clearly my line can handle better ?Even that shows tested data at 42 Mbps

As I said before last time this happened I booked and engineer visit as advised by BT support and the day of the engineer visit the rate mysteriously recovered.  Not sure if this is a broadband issue or a line issue. Can anyone help me understand who to complain to ?

[licquorice]

It is probably just simply another service has been provided to a customer and the resultant crosstalk has dropped your speed. DLM has absolutely no knowledge of any database and just automatically adjusts your line to give the best stable speed.

[prasadm]

Thanks @licquorice . Seems a bit odd that this has happened before and recovered, and now it has happened again at a 14 day reboot at midnight. And both times the speed it had dropped to is 37.13 ( please see the screenshots I have attached previously).

If the crosstalk has caused it, would you say the maximum data rate that I have monitored would have dropped too ? Or is it really not relevant ?

For a cross talk issue, would I need to complain to Line support or Broadband support ?

[licquorice]

Unfortunately, as your sync speed is way above your handback threshold, there is nobody to complain to. If it is crosstalk, then nothing can be done in any case.

[prasadm]

But they also changed the handback threshold midway through contract, wouldn't that count for something ?  It is like moving goalposts midway through a game, right ?

[prasadm]

@licquoriceToday I made a complaint to BT, and they booked an engineer visit. However a bit later, I had a call from BT who said they tested my line and has found no faults including crosstalk. I did tell her about the feedback I had from the community and she confirmed that there is no cross talk on my line. So if that is true then this drop in speed is suspicious and maybe linked to some other issue and maybe fixable remotely like last time, but that BT needs to check; as to what was done last time.

Not sure if there is anything more I could do. At this time none of this makes sense. I have a measurement of the line data rate that is running every 2 minutes capturing the NM and Max. data rate, and can't really see an issue there except that the NM is higher at around 7

[licquorice]

If your noise margin is at 7dB, DLM thinks there is a problem with your line.

BT wouldn't have been able to test for crosstalk, so not sure why the operative said that they had, unless they meant no crossed line which is something entirely different.

[prasadm]

If it is indeed crosstalk which caused this speed drop, then quite a few connections on that cabinet would have been affected, right ? Not just me ? And why is this fixed at 37.13 Mbps ? Is this the lower end of a band ? ( this is the same speed that was shown at the last time ( ~4 months ago) as well

[licquorice]

No, crosstalk doesn't affect every connection in the same way. It depends on where your pair lies in the cable compared with the disturber. Crosstalk is extremely complex.

It may not even be crosstalk causing your problem but DLM thinks something is wrong.