speed issues

rs6mra

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My fibre speed is rather slow around 1-2Mbps according to Speedtest.net.
I spoke to Plusnet and they have confirmed that all is normal at their end and ran a test on my line which was 30Mbps. What tech support also pointed out was that there was a massive upload late last night of about 30Gb and that is what may have affected the speed. I have been experiencing issues for the last 3 days and I have since found out that my daughter backed up the photos on her phone last night to iCloud. I just find it odd that this would be the cause.
Anyway, I was asked to check data usage on my PCs and one in the last 30 days that is hardly ever used had a total of 2,481GB of data usage in comparison to the one that I use every day which was only 232Gb. I have run malware and virus tests but this showed no results.
From the usage stats, the system used up 2,471Gb. Can anyone shed some light on this and have I anything to be worried about?
My line is still slow but Plusnet have now escalated the issue.
 
Whilst it may seem strange that a large upload effects your download rates, it's not a strange as it might seem:

Most of the network transfers we do, especially to/from the Internet, use a protocol called TCP (part of "TCP/IP" if you've heard of that.) Amongst other things, part of what TCP does is ensure that the data "gets there" intact and complete over otherwise "unreliable" IP networks.

In data networking the terms "unreliable" and "reliable" have a prescribed meaning not much different to the "natural language" use - basically "unreliable" networks do not guarantee delivery of data and do not provide any notification ("feedback" if you like) that data went missing (or got corrupted) to the sender and "reliable" networks do. It's kind of like the difference between sending a "normal" letter and one with recorded delivery. Ethenet, Wi-Fi, homePlug, IP are all"unreliable" - TCP layers some reliability on top of IP.

So all TCP transmissions are "positively acknowledged" in that the receiver tells the sender it got the data and/or requests re-transmission of anything missing or damaged. Albeit, that there is a kind of "rolling window" for a number of outstanding unacknowledged packets for performance reasons which I'll gloss over the details of for brevity.

So it's "send-a-packet" - "got-that-send-me-the-next-one" - "send-a-packet" - "got-that-send-me-the-next-one" and so on.

Now, if the the channel TO the nominal "sender" is full to capacity, it may be that it takes longer for the acknowledgements to get through, even if there's ample capacity on the channel FROM the sender and part of the performance tuning TCP uses means that it'll adjust it's transmit rate in light of how often it's receiving the acknowledgements.

So you can get situations where the traffic rate in one direction gets constrained, even though ample capacity is available, because the channel in the reverse direction is congested. Thusly on a SOHO ISP connection where the upload capacity is much lower than the download capacity, you could see this effect if there's a big upload going on and you try to download something.

At time of posting we are in the COVID-19 pandemic, and I think a lot of people using video conferencing are experiencing similar effects - their zoom calls etc aren't working so well even though they have super-fast (download) packages because their upload capacity isn't as good as download and getting congested which could be affecting quality if it's underpinned with TCP.

Any online video, of course, gobbles up data usage. Multiply that by the number of phones/tablets/TV/NetFlix/etc. And MS (for example) send out system updates often, and some of them can be quite hefty - again multiply be the number of PC's you have.

To know what's been used by what, you'd need to have monitoring technology deployed and it's practically impossible to do any analysis retrospectively I'm afraid. So we're pretty much guessing at what the usages may have been.
 
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