Infinity upgrade?

I've been on Infinity for a couple of months now.
At first, my ip profile was 38Mbps, then it went down to around 35Mbps, now it's currently at 31.8Mbps.
1. Is this decrease in speed part of a 'settling in' period?
2. Is it worth going for the upgrade to 80/20?
3. My upload profile is 10Mbps but speedtests have never been above 6Mbps, is this normal?
Thanks

1. It may be, it may also be if in a popular area for VDSL2 the increased cross talk
2. What does the checker suggest on a provider that is selling 80/20?
3. Have you tried uploading files and looking at the upstream loading? In case its the tester and PC performance

Just checked the upgrade on the BT website and this is what it came back with!!

Good news! We predict your download speed will now be 27Mb/s and your upload speed will now be 5Mb/s

Confused.com

In reply to a post by MrSaffron:

1. It may be, it may also be if in a popular area for VDSL2 the increased cross talk
2. What does the checker suggest on a provider that is selling 80/20?
3. Have you tried uploading files and looking at the upstream loading? In case its the tester and PC performance

1.A few of my neighbours have recently signed up so I assume this is the cause
2.Not sure where to get this?
3.Is there an easy way of doing this?

1. Hard to know without a good history of line data
2. See you found this, and as profile 17a has been running for a while too. So really is now a case that only those seeing 40 or 10 will get much of a boost.
3. FTP uploads, online backups. If you don't do that much upload then don't worry about it.

In reply to a post by MrSaffron:

1. Hard to know without a good history of line data
2. See you found this, and as profile 17a has been running for a while too. So really is now a case that only those seeing 40 or 10 will get much of a boost.
3. FTP uploads, online backups. If you don't do that much upload then don't worry about it.

Not sure I understand your second answer, is it a typo?

17a refers to teh variant of VDSL2 that is used. There are four main ones: 8, 12,17 & 30 which refer to bandwidth in MHz used in the modulation scheme, so te original was 8MHz and now BT have moved up to a 17MHz.

The letter, a, b, c &c refers to how the upstream and downstream segments are allocated within te bins available and BT went for Band Plan a.

In answer to your earlier question, having dropped from 38 to 31 - that is almost certainly due to extra noise from crosstalk and as you are well below 40 at present it is unlikely you will see much of an increase by moving to a 80Mb product as you would have experienced it already as the 80Mbit capability is there but had been capped to 40Mbit.

Thanks for the explanation.
When you say 'extra noise from crosstalk', what does that mean?

A simplistic explanation - not exact but will help.

When you put an AC signal down a wire some of it will be radiated out rather than going from end to end - similar to an antenna but very inefficient. And there will be quite a number of other circuits running VDSL2 in the same cable bunch as yours and everyone will radiate just a little - and it will all be "in band" - that is the same frequencies as your VDSL2 signals.

Your copper pair will absorb some of the radiation from each of the others and as it is not part of your signal, it will look just like noise to the modems.

In return for the other parties causing interference to you, your wires also radiate and cause problems for the other!

The radiation from one pair and absorption by another is called "crosstalk".

There is not much that can be done - twisted pairs helps but is not perfect, separation is also beneficial but impractical. Vectoring, which might come out with the 30Mhz scheme tries to predict noise based on various factors and then injects an inverse signal but is still not perfect. It is a technique successfully used in other areas including noise cancelling headphones ...

My current FTTC speeds are 31/8, predicted speeds are:
50.7Mbps download (10.9Mbps upload)

I am approx 480 metres from the cabinet and there is a train station between the cabinet and my place which according to the BT engineer will affect my speed. Because it is a Business line I would have to start a new 24 month contract which only started in August.

Pondering on whether or not to risk going for the extra capacity or just leave it.