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Author Topic: Coincidence or something more?  (Read 685 times)

AndrueC

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Coincidence or something more?
« on: January 22, 2018, 12:32:36 PM »

Last August openreach relocated my PCP. In June I changed ISPs and during transition my PPP connection was down for 18 hours (because I hadn't noticed and forgot to change the credentials when I left for work). Up till that point I'd had a solid 67Mb/s according to speed testers for a couple of years but after changing ISPs I only got 55Mb/s. Over the following months I had a couple of early morning drops but nothing much changed.

This weekend I decided to set myself up to backup a large amount of data to the cloud. About forty minutes into the upload (while I was out) my line lost sync and my HG612 failed to reacquire it (or couldn't be bothered). So when I got home I had to power cycle the modem.

I'm now back to a 67Mb/s throughput. I mentioned this to a friend and they reminded me that they had a similar experience. A long period of poor sync speed apparently 'cured' by sending large amounts of data upstream.

Is this a coincidence? My line is normally completely stable so having the line drop in the middle of the afternoon is rare. I'm just wondering if, maybe, the upload traffic caused the DLM to re-assess my line and restore my original sync speed. For what it's worth although my downstream dropped with the change of ISP my upload appeared as good as ever at around 18.5Mb/s.

Sadly I don't currently have an unlocked modem so can't provide stats.
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richi

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Re: Coincidence or something more?
« Reply #1 on: February 18, 2018, 01:59:38 PM »

Retrains during darkness or early morning are likely to allocate fewer bits per marginal bucket than retrains during the day. Because ionosphere.

Might this explain it?
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j0hn

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Re: Coincidence or something more?
« Reply #2 on: February 18, 2018, 02:31:43 PM »

DLM doesn't know or care if you are uploading.
The increase in sync is 100% unrelated to the fact you were doing an upload.

The max attainable (the potential sync if resynced at that moment in time) of a line fluctuates throughout the day. On some lines this changes by 2-3Mb between day and night.

The attainable also changes with crosstalk. Crosstalk is the noise created by neighbouring phone lines. Some of your neighbouring lines will have been 1-2Mb upto as much as 20Mb difference to your attainable wether they are online or not.
If my neighbour turns off his modem my attainable jumps 4Mb. If I resync at this point I get an extra 4Mb sync.

There's a dozen reasons why your sync will change when you perform a manual resync.
The fact you were uploading isn't 1 of them.
It isn't even DLM related unless there have been a large number of resyncs preceding it.
DLM will not change the lines profile for performing a single manual resync.

TL;DR.... coincidence.
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richi

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Re: Coincidence or something more?
« Reply #3 on: February 19, 2018, 10:21:17 AM »

There's a dozen reasons why your sync will change when you perform a manual resync.
Here's another bizarre one: If you don't get many incoming phone calls but you recently received a call, the ringing current may have repaired a marginal HR joint. True story.
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