Effects of crosstalk on FTTC

Are there any reliable figures for how much crosstalk is affecting FTTC lines? In the last month or so I've seen around 20Mbit shaved off my speed, from a high of around 72Mbit to now being the low 50s. I've tried repeated early morning re-syncs, but it hasn't improved.

Edited by deleted (Tue 18-Jun-13 11:26:20)

no because its inconsistent.

I suggest you unlock your modem you can then see if there is any point in resyncing by checking your snrm.

Have those been modem or router resyncs?

Best to leave the modem well alone; it's sync speed will increase automatically when (and only when) DLM permits.
Too may resets and DLM may lower your speed.

What is needed is a router PPPoE disconnect/reconnect; to force the IP profile to match the sync speed.

As Chrysalis says, if you have an unlocked modem, you will know when it is worth disconnect/reconnecting the router.
However, too much router disconnect/reconnecting or resetting won't do any harm.

I too have had a massive reduction in speed. I used to have around 78Mbits and now around 50's, I've been on to BT who sent three engineers out, the first two said that the speed I'm currently getting is the best I can get? Which I found extremely amazing as I�ve had a totally stable line and have always had good speeds. Anyway on the third visit the engineer told me that they only have 4 weeks of data to show what speeds I�ve been getting, so if you don�t get onto them straight away you don�t seem to be able to support your claim!! *very annoying* The engineer did resolve the issues by resetting something (no idea) and I was back to my �normal speeds. A few weeks later and it�s all happening again! ..the thought of having to go through the very tiring conversation with the Indian call centre and take more time off work to get another engineer round is draining!

What may have happened is that the engineer reset your profile without fixing the fault which caused DLM to lower your profile, so DLM has again lowered your profile.

You need an engineer to fix the fault.

May be, what is strange is that its taken weeks for the fault to happen again?

These have been modem resets. I really do need to bite the bullet and flash the modem to get some stats. I've not bothered before just because it was working fine, and I didn't feel the need to tinker for the sake of it. A far cry from the DMT days of tweaking my SNR margin to get the most from my 5Mbit line. The resets have been fairly infrequent, maybe once a week 3 or 4 times. Is that likely to cause trouble?

It's a shame you didn't manage to grab any stats & graph them when the connection was at its best as 'evidence' that it has now deteriorated.

My connection has dropped from a steady sync speed of just below 30 Mbps to just over 20 Mbps since December 2012.

I can see changes in in my QLN graph that points to it being increased crosstalk.

BT's response was to lower my speed estimate from 30 Mbps to 23.3 Mbps, so I am now no longer suffering from a 25% speed drop from estimated speed that is apparently some sort of fault threshold.

2 engineers have visited recently & carried out the usual PQT & Eclipse test, both passing with flying colours for line quality, but the most recent engineer did phone someone who confirmed that my cabinet is now almost at capacity - again indicating increased crosstalk as the likely culprit.

From what ive seen, each line added to my cab shaved 0.6dB off my SNR.

my cab is now full 6 months after it got made live.

I have 4 known instances of loss of snr/sync speed.

in order

#1 15mbit lost by 1 line.
#2 18mbit lost by 1 line
#3 2mbit lost by 1 line
#4 2mbit lost during fault period/engineer.

so first 3 crosstalk loss's by 3 lines, and the other 120 or so lines in cab no affect on my line.

on my line 3db of snr is about 13mbit of sync speed. so based on that can guess snr impacts.