You appear to be on the 40/20 product and not quite attaining 40Mbps throughput.

Plusnet are limiting it to 40Mbps maximum throughput because of the product you are on. Knock off a bit for packet overheads and the Plusnet disappearing 2Mbps compared to BT and 36Mbps of data on speed tests looks fine to me.

What's the problem?

Edited by RobertoS (Tue 05-Jul-16 18:37:28)

Well, BT and Plusnet thought there was! You don't. I cannot question their knowledge.

Edited by mikejp (Tue 05-Jul-16 20:00:52)

But do BT know your throughput is capped at 40Mbps. They won't know anything about that. There is no such BT or Openreach product. They will be looking for why it isn't achieving what it should on 80/20.

In other words your IP Profile is probably 47.43Mbps and they will expect much more than 36Mbps throughput. They won't find a fault because there isn't one.

It would help if you also distinguish between BT Retail the ISP and Openreach . I can't see what either has to do with it so no idea which of them is saying there is a problem.

Edit - reading back it seems you are referring to the BT Wholesale Performance Test. The same applies - it will be comparing the throughput with the much higher IP Profile. That isn't a problem, for the reasons given.

Edited by RobertoS (Tue 05-Jul-16 20:04:47)

Quite simply, the longer the copper (or aluminium) phone line is, from the new FTTC/VDSL source, via the old PCP distribution box, to your house, the slower the VDSL will be, as measured by practical Speed Testers such as TBB's.

Your "6 - 700 metres" looks as though it is a guestimate, and you have made no attempt to define how it was "measured".

You haven't said how you arrived at that figure, whether it is a straight-line measure, or actually directly measured or some other variant.

That length has an absolute effect on the working speed that you get.

http://www.increasebroadbandspeed.co.uk/2013/chart-b...

http://www.speedguide.net/dsl_speed_calc.php

http://www.ewhurst-broadband.org.uk/?p=1526

http://www.zhone.com/solutions/docs/VDSL2_Primer.pdf

All clearly state that the Line Length (or Loop Length) are critical to the performance of VDSL, hence needing to be certain of that length when assessing working speeds.

Hence asking how you have arrived at the figures of "6 - 700 Metres".

As does the general quality of the line, including noise.

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As I have indicated before, my line superficially looks as though it is 100 Metres long, which should give me very close to the ("up to") 40 Mbps on the contract - but in fact it is about 300 Metres long, hence the speed dropping to around 36 to 37 Mbps.

That length was initially established when a PO lad, trying to clear noise on the line and having remade all the obvious joints and not clearing the problem, took a closer look at the records, then we both proceeded along the road away from both PCP and my house, to a very small junction box that showed up on the foundations of a near-neighbour's house, about 125 Metres away, opened it up and re-made the joints in that - clearing the fault.

I have since confirmed it by Google Earth, also separately adding the lengths of the individual houses passed including the short right-angle crank in the footpath etc.

His sync speed and attenuation tally with 6-700 metres.

We seem to be at crossed purposes here, eckiedoo,
"Quite simply, the longer the copper (or aluminium) phone line is, from the new FTTC/VDSL source, via the old PCP distribution box, to your house, the slower the VDSL will be, as measured by practical Speed Testers such as TBB's."

I thought this line length would be reflected in both the sync rate and max attainable, but you suggest it would not be and would only show in the TBB download test?

Line length paced, so within 8%, if it matters!

Agreed - but he does not appear to understand this relationship, being misled by the sync rate etc.

Take a look at the small graph, at top-left of page 2 - and then consider whether line length matters or not-

http://www.zhone.com/solutions/docs/VDSL2_Primer.pdf

Be wary, the X-axis is in "Kft", ie 1,000 foot intervals and is the length/"Distance" of the line involved.

The Y-axis is in "Mbps" and technically the description, "Data rate" is more correct than "Speed".

Note how both the VDSL1 and the VDSL2 plots tumble down fast, rather like the depreciation of car values; particularly how low they are as they intersect the "2" (2000 feet, about 606 Metres).

As Robertos has said, the "Speed"/ Data rate loss that you are encountering is generally close to what can be expected and tolerated, given your stated Line Length, and your stated Attenuation.

The two graphs at the foot of Page 2, generally confirm that loss with increasing length.

----------------

Keep in mind also that there are many other aspects that affect the arrival of the data at your location, search for-

vdsl data packets sync

http://www.kitz.co.uk/adsl/interleaving.htm

Although this is describing ADSL, VDSL is similar.

----------------

Regarding "Speed" or "Data Rate", I raised that question at my first ADSL training session, with the Instructor, at the mid-morning break.

He had been using "Speed" throughout.

Privately he agreed that it should be "Data rate"; but somehow the Development Team/s had fallen in to the habit of using "Speed" and that was what was in most of the literature of that period; and has continued to be so.

---------------

To get an impression of how confusing it is, try doing a Search for-

speed of electricity in wires

"but he does not appear to understand this relationship, being misled by the sync rate etc. " - well, I think he does, but please explain how the sync rate & max attainable detected by my router is not correct but needs to be corrected for line length?

All you keep posting is that speed drops with line length!

Roberto - I agree with the logic of what you say, but SUPPOSE I had a profile of 47'ish - what I am seeking is the reason for the loss of the 4-6Mb that I experience, and why the line is performing below par according to BTW. I cannot recall the figure BTW produced as 'target' - it was a while back and ithe results went off to PN - but I think it was up around 38. To my simple mind, with that IP profile and a '40Mb' Plusnet contract, I would expect much closer to the 40.

At what point is the '40' limit imposed by PN? As you say, I doubt BT know my 'limit', so one assumes my line carries 78/19 to be affected by line length and attentuation/noise and then somehow by PN. What is this "Plusnet disappearing 2Mbps compared to BT"? Are you saying they themselves are 'throttled' such that a '40' product will only ever max at 38??

Because as can be seen on the various sites, Speed (actually Datarate) does drop with line Length.

There is a legal maximum limit to the Voltage that can be sent down phone lines, that drops due to the Resistance etc, thus gradually that diminishes due to the combined effects of Resistance, Capacitance and Inductance, in combination known as Impedance.

Thus rapidly for VDSL as shown on the referred graphs, that (signal) Voltage reduces to below levels that can be detected by the Broadband equipment, or "lost" in any general noise on the line, hence the QLT.

Also, generally the communications involved, say a file transfer, is broken up into "Packets" of about 1500 Bits (or fewer), each with Headers and Trailers within each Packet, giving the To & From addresses, rather like an envelope, so a 1.5 Megabyte file is broken up in to about 1.1 Million Packets, each of which has to traverse the intricacies of the Internet safely, including additionally sending back messages in similar packets, to confirm Safe Arrival, or the Receiving end notes that one or more Packets are missing or don't pass checking, so requests that those be re-sent, hence extending the total time involved compared with the ideal time.

Even the smallest Packet has a full Header and Trailer, say for a 1 Byte content. The smaller the Packet size, the less efficient is the system.

And each Packet, large or small, can take a distinctly different route through the Internet/Web - that is part of the resilience of the system.

I don't claim to know "all of it", far from that, it is a highly complex subject.

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If anyone is aware of a good primer on the subject, I for one, would welcome it.