Both on the same drop, both sockets next to each other. Both are ECI.

If you were just seeing a drop in performance generally over time, I'd put that down to crosstalk if your line was marginal that it could only just achieve the 80/20 speed (mine has sufficient margin that it could go significantly faster if it was an option).

My hunch is that the piles of brown stuff like the Home Hub are introducing lots of interference to cause such a major drop. I have nothing good to say about the kit BT chuck out - the wireless is pathetic, the sync capability poor, the functionality laughable. Total garbage but sadly BT continue to get the majority of the broadband business.

I've yet to see any of our customers suffer significant drops in speed.

Edited by therioman (Sat 23-Aug-14 08:33:57)

I only went with BT because the kids wanted BT Sport, after factoring in the cost of that per month vs free with BT over 18 months, plus I got £120 quidco cash back and £60 Sainsburys card, it seemed a good deal, Sky weren't interested in giving me a good deal, preferred to lose me!

I thought BTOR would install their own modems but alas not. First thing I had to do was disable all the poop on the HH5 and HG635, all I need is modems, the wifi and firewalls are all disabled.

My sockets are separated by about 13m, drop wire is about 33m to split then 1m to BT socket and 12m to TT socket.

Hi

It is crosstalk and nothing you can do about it unless you can physically separate the pairs. Your pairs are very likely running together from your home all the way to the cabinet, and so is worse case scenario for cross talk.

Any changes, and yes improvements to the lines, could see speed reduce a little, for example the DLM backing off the power because the line has less errors and it is detecting crosstalk which it is trying to mitigate. Or it could just be while the work was being carried out some one else connected up to VDSL, causing more crosstalk.

It is an industry known problem using telephone cable that was never designed to carry these frequencies, you will go mad trying to fix it. Best hope is vectoring, even then the improvement might only be slight in worse case scenarios like this.

Regards

Phil

Bipac 8800NL Hooked up on TT, think DLM is limiting as attainable shows 102084 but sync is 53980 19.8dB SNR Stats below, first number download, second upload, will now hook another 8800NL onto the BT line and see if it drops the same.

Line Coding (Trellis) On On
SNR Margin (dB) 19.8 11.9
Attenuation (dB) 15.9 0.0
Output Power (dBm) 13.9 6.8
Attainable Rate (Kbps) 102084 32678

Rate (Kbps) 53980 19999

B (# of bytes in Mux Data Frame) 239 47
M (# of Mux Data Frames in an RS codeword) 1 1
T (# of Mux Data Frames in an OH sub-frame) 64 52
R (# of redundancy bytes in the RS codeword) 0 16
S (# of data symbols over which the RS code word spans) 0.1415 0.0763
L (# of bits transmitted in each data symbol) 13568 6714
D (interleaver depth) 1 421
I (interleaver block size in bytes) 240 64
N (RS codeword size) 240 64
Delay (msec) 0 8
INP (DMT symbol) 0.00 4.00

OH Frames 0 0
OH Frame Errors 0 0
RS Words 0 3858496
RS Correctable Errors 0 43
RS Uncorrectable Errors 0 0

HEC Errors 0 0
OCD Errors 0 0
LCD Errors 0 0
Total Cells 296577803 0
Data Cells 4120974 0
Bit Errors 0 0

Total ES 0 0
Total SES 0 0
Total UAS 33 33

Yes, DLM it is.

Both lines have now got 8800NL modems on, things are similar as expected but at least I can see some stats.

The BT line max rate tops out at 87M, TT 102M even though TT is 13m longer.

The whole tone spectrum is about 5dB worse SNR until you hit tone 3400 where the BT line rapidly rolls off to 15dB SNR at the top end, the TT line still has about 28dB SNR at the highest tones.

The high frequency performance of the BT line is quite a bit worse, should 2 lines differ in performance this much?

Regarding the crosstalk, nothing I can do, BTOR have made it much worse, max rate drops 44M on the TT line 102M to 58M and the BT line drops 31M from 87M to 56M

BTOR coming back Tuesday, what should I ask them to do as I don't think they know how they have made it worse. I am thinking insist on a second drop wire as that seemed to lose 20M ish off the speed??

Sounds like a plan. He must have done something wrong...

I've done some more analysis on the 2 lines, this is with only one modem on at a time, both lines using bipac 8800NLs with latest firmware, should 2 phone lines differ as much as shown in the graph in the link below, the Talktalk line is longer but better across the whole spectrum, even more so towards the higher frequencies, graph here:-

SNR Per Tone

Two lines may share the same drop wire to the home, but be in different bundles and even different routes back to the cabinet. Though with FTTC the chance of this is lower than it was with ADSL services.

The trick is the to get your VDSL up and running and rebooted and check the same graphs ASAP after a power cut or during a power cut if you can. i.e. when cross talk from other lines is likely to be at its lowest.

I'm in a very small village and from what BTOR told me there's not many fibre conns yet, I had connections 1 & 2 and they had done 2 others I think.

I hooked a spectrum analyser onto the BT line, image at link below, blue trace is how the line looks from 100kHz to 18MHz with both modems off, when I switch the Talktalk line modem on you can see the level of coupling especially in the block between about 8.5 and 12MHz

VDSL Crosstalk