i'm trying to anticipate what speeds i can expect when the cabinet i'm on goes live and i'm surprised at the high figures on the checker as i'm approx. 650M from the cabinet.

FTTC Range A (Clean) 77.5 59.1 20 18.6 -- 31-Mar-14
FTTC Range B (Impacted) 66.8 38.1 20 13.3 -- 31-Mar-14

from what i read on here, i'd have thought anything over about 30 would be doing well at that distance. in fact i think they have risen again today.
i know that BT can measure the line attenuation for the whole distance, but wasn't convinced that these estimates are taken from cab to subscriber meterings.

In reply to a post by cookie:

i'm trying to anticipate what speeds i can expect when the cabinet i'm on goes live and i'm surprised at the high figures on the checker as i'm approx. 650M from the cabinet.

Your figures do seem rather high Perhaps the lines in your area are newer or of higher quality than average though, the sort of thing the checker is probably aware of.

Are you sure you have the correct cabinet?

Does it have your number on it?

In reply to a post by cookie:

i'm trying to anticipate what speeds i can expect when the cabinet i'm on goes live and i'm surprised at the high figures on the checker as i'm approx. 650M from the cabinet.

FTTC Range A (Clean)	77.5	 59.1	20	18.6	--	31-Mar-14
FTTC Range B (Impacted)	66.8	38.1	20	13.3	--	31-Mar-14

My old house was 650 metres from its cabinet, on 1990's copper. With the old 8c profile (using 8MHz) it could get 40Mbps, but was reduced to around 36Mbps by DLM. Once the 17a profile was introduced, this jumped to a clear 40Mbps. We never had the option to try 80Mbps on it - but the recent estimates have been around 48 Mbps.

The estimate today is:

FTTC Range A (Clean)	68.1	50.7	20	14	--	Available
FTTC Range B (Impacted)	57.4	32.3	20	9.9	--	Available

i know that BT can measure the line attenuation for the whole distance, but wasn't convinced that these estimates are taken from cab to subscriber meterings.

I suspect not too. More likely that they measure from exchange to sub, and then subtract an amount for the exchange-cab path.

On the other hand, I've also seen something that says the estimates are really based on the cab-DP portion alone. I have no idea about the truth of this, though.

Testing the line with a TDR will tell you the electrical distance to each discontinuity in the twisted pair, so identifying the electrical position of the cabinet, the DP and the NTE should be pretty easy.

No time to dig out stuff in Google, and it's far too long since I did transmission line theory, but with some clever maths I'm pretty sure you ought to be able to get a pretty good estimate of the AC attenuation of each section of the line. I'd put good money on standard exchange/central office test kit doing this.

yes, it is the right cabinet and it is numbered as per the checker.

A paper for NICC DSLTG by John Cook presents the cumulative distributions for BT�s network of line length for exchange to customer and cabinet to customer in the form of attenuations.

BT are aware of what all the line lengths should be, looks like John Cook converted that to attenuations using a formula.

BT won't have tested the attenuation of every loop because they can't - what about the unbundled ones?

In reply to a post by mpellatt:

Testing the line with a TDR will tell you the electrical distance to each discontinuity in the twisted pair, so identifying the electrical position of the cabinet, the DP and the NTE should be pretty easy.

Unfortunately lines generally aren't one long contiguous piece of copper from exchange to PCP.

my line is now below the estimated clean range. Of course I am still trying to find out if I am the only one who's previous estimate si the same as the new impacted low estimate.

I now have the new firmware, and sync speed is down, errors up, and lots of weird data on my new graphs such as

lower attenuation on the upstream tones than downstream tone, whats that about?
higher snr strength on the upstream tones vs downstream tones, even when QLN is equal.
clear power cutback on my U1 tones, probably explanation for my 9mbit of lost US attainable.

On the old firmware I couldnt see the upstream data so didnt know this before.

Also that I have a engineer booked for HR check, but it got cancelled as openreach says is major fault in area affecting many lines but wont say what it is.

The BT checker thinks my clean rate is the full 80/20:

FTTC Range A (Clean) 80 63 20 20 -- Available
FTTC Range B (Impacted) 71.7 44.1 20 15.4 -- Available

I don't actually get anywhere near to the clean or impacted maximums. I haven't looked in a while but it's something like 65/20, or 71-ish after a power cut where (presumably) there is minimal crosstalk before all of the modems sync up.