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.

All this hype about FTTC! In the long run it could well be better for a fast ADSL2+ line like mine, say > 15 Meg, to never move to FTTC .

i guess with my cab being fairly new the effects of crosstalk have yet to impact my speed only time will tell whether it was was worth upgrading from the 17 -18meg i had on adsl2+ lol but for the mean time im happy.

actually thining about it i may already be suffering some sort of crosstalk for instance early morning 7.30am i can get a consistent ~71meg down and 18.84 up but by teatime say 5:30pm i can only get ~67meg max unless thats just normal TalkTalk congestion? on adsl2+ i got line speed 24/7

I started off at 79999 with an attainable in the low 90s. Nearly 18 months on and it's 65Mb/s with interleaving. It's been that way for several months now though so seems stable. DLM has tried to turn off interleaving twice this year. Once it lasted two weeks, this time it lasted a couple of days.

In reply to a post by Bald_Eagle1:

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.

Classy

In reply to a post by XRaySpeX:

All this hype about FTTC! In the long run it could well be better for a fast ADSL2+ line like mine, say > 15 Meg, to never move to FTTC .

LOL, I wondered as much before I moved, 16meg download / 1meg upload - has gone to 45meg download / 8meg upload - both as measured by this sites speedtest web page.

I'm hoping I'm in the lucky zone and won't see any slowdown over time. I'm now in month 9 of an 18month contract.

Just my 2p worth.

Don't know what the main causes of this loss of bandwidth by crosstalk, but I live within 3 miles of Central London and my connection has been stable @ 79992/20000 since it was installed 04/12 [touches wooden head :)] and I would expect that my cabinet is fairly near to capacity.

I do suffer from slight losses of down/up speed at various times due to congestion/latency

You must be quite close to the cabinet with those sync speeds, so potential crosstalk is probably not that much of an issue for your connection at its capped 80/20 speeds.


Have you seen a general decline in attainable rates since installation though?


A symptom of crosstalk can usually be seen in a 'worsened' QLN graph.
Do you have any of those for comparison?

Edited by deleted (Sat 22-Jun-13 09:15:00)

Distance is in my sig, but I have seen others in here that have/had the same sync speed and are having problems, My max attainable has never been much greater than my sync.

As I said I get the ocaisional slight slow down in down/up speeds especially around 09/10 in the morning (offices starting up) but nothing general, my SamKnows charts are almost straight lines every month

In reply to a post by XRaySpeX:

All this hype about FTTC! In the long run it could well be better for a fast ADSL2+ line like mine, say > 15 Meg, to never move to FTTC .

Well I have no intention of swapping over.
Surbarban market 2 exchange, due for conversion to FTTC - 'sometime'
100 m from the cabinet, 13Mbps download on ADSL2+, a steady good line. I as sole occupant have no need personally for any more and certainly no justification for the extra cost of FTTC.

So, no at the moment I won't be upgrading to FTTC.
Maybe by 2020 they will be offering FTTC for the same price as ADSL as by then some new super mega ultra high speed broadband will be here - at a premium price of course. So probably then I'll upgrade to FTTC.

In reply to a post by XRaySpeX:

All this hype about FTTC! In the long run it could well be better for a fast ADSL2+ line like mine, say > 15 Meg, to never move to FTTC .

probably not.

since my attainable started out at 110 I still have a sync speed of almost 70mbit. with an upload sync speed of 20mbit. Not to mention the line is way more stable than I had on adsl. So its still light years apart.

Unlike andrue I am still on fast path, the engineer fixed the issue (although he said he didnt) that was upsetting DLM.

Edited by Chrysalis (Sun 23-Jun-13 06:06:49)

Where are you finding the information on cabinet capacity?

I noticed a new cabinet been installed, and I spoke to the guys installing it.

also checked with my install engineer afterwards.