BT FTTC Estimates vs Reality

About to get install of VDSL next Tuesday. BT Are quoting Range A 33.2 - 24.1 Range B 26.2 - 13.3 . My home wiring is fine. What are people normally seeing as the reality the Low or High end? I notice that the ISP's all quote "Up to 24.1" as my estimated speed, is this being cautious too?

It varies is the best (but not most useful answer).

I am currently in the middle of my quoted A range; at 65 in a range 56-74. When I first connected a couple of years ago (after a slight hiccup due to internal wiring) I was above the top of the A range, at around 70 for a quoted A range max of 58. My speed went up at one point, and the estimate at another; and until a few days ago I was at 72 in the range 65-74 for quite a long time. I think from reading other posts on various forums that it is fairly typical to be in the upper half of the A range. However, there is a very significant proportion who fall well into the B range, or even below it; of course these people are much more motivated to post on forums. (basically, just a long-winded way of saying what MrSaffron said)

Quoted speeds are line speeds. Profile will be a fraction below line speed, and on a good day, downloads a fraction below that.

Edited by StephenTodd (Wed 24-Sep-14 14:25:01)

Reality ... anywhere from 13 up to 35! There is no way to tell until it is actually installed and tested. Some customers are unlucky and get a line that is prone to noise and others get a nice clean signal.

In reply to a post by plankton:

About to get install of VDSL next Tuesday. BT Are quoting Range A 33.2 - 24.1 Range B 26.2 - 13.3 . My home wiring is fine. What are people normally seeing as the reality the Low or High end? I notice that the ISP's all quote "Up to 24.1" as my estimated speed, is this being cautious too?

I think you're failing to understand what an estimate is

No, I understand the concept of estimate, but curious to understand the reality of distribution with in the estimate.

In my case the download speed estimate is 36-51mbps and the upload 8-13mbps.

The thinkbroadband speed test results are (avg) 52.97 down and 8.86 up (line sync speed are, of course, about 5% higher). I should note that download had dropped to abut 35mbps and upload 5mbps until I reported a fault which was apparently due to an imbalance. (Nothing to do with the internal wiring I should add - that's pretty well optimal).

I suspect that for the vast majority speed estimates are accurate, but only where there isn't a line fault. I'd also add that I think upload speeds seem to deteriorate more than download as cabinets become more utilised, probably because of increased cross-talk at the DSLAM end (which makes sense as that's where the signal is weakest and there are the largest number of cables in close proximity (in contrast, the download signal is strongest at the DSLAM send it's less vulnerable to cross-talk. I saw this in that my original upload speed was over 12mbps (losing almost 30%) whilst the download has deteriorated by only about 5% since the cabinet was enabled. There seems to be less sign of deterioration of throughput due to cross-talk now.

nb. I've no idea what the original estimate was. It's very likely Openreach tweaks estimates according to real results on the cabinet.

In my case, the estimate is 60/19-79/20 clean and 44/14-71/20 impacted.

The line is clean, and gives a nice smooth Hlog graph.

We've had 80/20 line speeds for the best part of 3 years. Crosstalk has been increasing gradually, so the best we can do now is 79/20 (matching the top of the clean), but we are close to DLM intervention on the current error rates. When DLM intervenes, we end up at 72/20.

My estimate was 63 Mbps and initially I got 74 Mbps but now it's down to 55 Mbps which, according to the engineer that last visited, is down to deteriorating joints between aluminium and copper cable. Unfortunately where the cables join was sealed in some sort of epoxy compound which he hadn't seen before. He also said there didn't appear to be any crosstalk issues.

He tried another pair but could only get the line to sync at 38 Mbps.

AIUI the "Impacted" (B) range is allowing for imperfect home wiring. In the days of "engineer install only" that line didn't exist, and when it came in the A range was the same as the previous only range.

If you are an early adopter on your cabinet you are likely to be somewhere around the top of the range. As the cabinet becomes more and more populated it is probable the real speed and the estimate will decrease, due to new crosstalk. If you are not an early adopter, you will just slot into the range somewhere, depending on the take-up there.

Unfortunately the crosstalk isn't simply dependent on the number on the cabinet. It is very dependent on the proximity of in-use pairs. You could see many join and have no effect, then one more really hits you. Alternatively, that one is the first after you and you get hit immediately but then stay stable. Or, it's your joining that hits that one and you start off affected! Plus any permutation you care to think about wrt such factors.

What is guaranteed is that unless what you get is clearly a fault, (and that can take a long time to prove), you get what you get and Openreach don't give a damn. As a result, your ISP can do (many censored words) very little.

A final factor is Interleaving. If that kicks in the normal (lowest) hit is about 10Mbps with a latency increase of 8ms. Unlike the old ADSLx DLM interleaving however, this one does revert to Fast Path if it proves over a couple of weeks or so to have been an isolated burst of errors/noise.