Is the old extension still connected to the unfiltered line? If so, it will act as a "bridged tap" and that (especially on VDSL) can lose some speed at the master. Note that it doesn't matter if the extension is not used. The solution is either to disconnect the extension completely or connect it via the filtered output on an Interstitial adapter or a VDSL faceplate. (Of course this is true for any other extensions too).

If you sync via the test socket (removing the faceplate) and find that your sull sync rate returns (or better), that will almost certainly be the issue.

Tried the test socket and gained very little about 100kbps. I was tweaking SNR to 1.5db but since interleaving kicked in I have had to use 2.0db as it just wouldn't hold sync.

Looks like I'll have to live with it.

Tweaking increases sync speed (which is what you intend), which increases error rates. That, plus any losses of connection, could be the cause of the interleaving in the first place.

In other words, it's quite possible you have over-tweaked and ended up being counter-productive. It was fine on O2/Be and think Sky, where the DLM was basically deactivated after the first three days, (ceased to be dynamic in fact), but on a BT Wholesale service it really is on all the time.

That's why for many years the default sync-time margin was 6dB. These days the BTW DLM will drop it to 3dB when appropriate, in fact sometimes when it isn't. We have had people having to get their ISP to get it fixed at 6dB because of 3dB being unstable.

It's worth keeping an eye on the FEC and ES/SES rates. Huge amounts of FECs can kill the router CPU and really slow down the throughput.

100kbps change on a re-sync is basically "no change". More than that much fluctuation is normal.

Interleaving kicked in after a phone fault Im pondering getting it switched off at ISP.

In reply to a post by RobertoS:

Huge amounts of FECs can kill the router CPU and really slow down the throughput.

Do you have some guidelines as to how huge is 'huge' (per unit time)?

Do you have some guidelines as to how huge is 'huge' (per unit time)?

My adsl drops (sometimes) when I get spikes >50 to 70 thousand per min, these normally happen when lightning is in the vicinity.

My average 24 hr total is about 100,000, with a few few spikes of about 2500/min

Ian

In my case I was very aware of it at several thousand per millisecond . Where it becomes critical I have no idea, but a million or so a day doesn't seem to bother a 5Mbps ADSL2+ line.

It will of course depend a lot on the modem CPU rating.

And, of course, OP will only see FECs if on Interleaved, not Fast Path.

Here's what routerstats says I presume Reed Solomon is FEC?

Noise Margin: 2.3 dB
Line Attenuation: 27.5 dB

SuperFrames: 3333127
SF (CRC) Errors: 124
Reed Solomon: 773285688
RS Corrected: 11330899
RS Un-Corrected: 7036
HEC: 119
Errored Seconds: 115
Severe ES: 0

Interleave Depth: 96
Bitswaps: 69

Total Uptimes (From SF counts):
WAN: 0 days, 15:01:30

Edited by Banger (Mon 19-Jan-15 00:43:12)

Reed Solomon is the error correction methodology, and I think that counter is the number of packets received,

RSCorrected is the FECs and RSUn-Corrected the ones it couldn't. Both are packet counts. The uncorrected ones require a "stutter" while they are retransmitted.

You are running at around 800,000 FECs per hour. That is why the DLM has put you on interleaved. No doubt about it. You need to sync untweaked and see what happens to the error rate.

Note that even when you are not using the connection there are packets passing continuously all the time. Just with no data in them. Like a stream of empty addressed envelopes coming through you letterbox. The transmission or not of data makes no significant difference to the error rates.