BT Infinity Sync/Speed drop

OK... please bear with me.

Moved house 4 years ago. Had infinity 2 installed. Have been running at top 80/20 speed up until recently. About a year ago swapped hub for Billion 8800NL and could see my max attainable rate was around 88000/90000 and I was on 79999/19999 speed. This has been like this up until about 3 weeks ago.

Kids complained that they had issues with xbox so looked at router stats and I'd dropped to 20000 down despite max attainable rate still being around 88000. Rebooted router and my max attainable rate dropped to 71000 and my speed was 71000. Rebooted again, stayed the same. Logged a fault with BT. They did some checks outside and said there was a line fault. They worked on it while I was away on holiday and I chased up on my return last weekend. They said they had fixed it, but my max attainable rate had dropped further to 68000 and speed around 67000.

An engineer has just came round and checked the line from my internal socket and said there's no fault. He's requested a line reset and told me about the 10 day retrain. I've currently got a max attainable rate of 69000 and a current speed of 59000.

Really don't know what to do as I'm about 200-250m from the cab and the cab is about 20m from the exchange.

Massively frustrated, any advice?

Edit: Added some screens of router stats at various points:

Normal stats as in pre-fault for the last 4 years
Pre-Fault

Post-Fault
Post-Fault

Just now, after reset
Current

Edited by deleted (Mon 11-Jun-18 14:47:51)

10 day retrain - and I won millions on the lottery at the weekend, both are equally false.

On a DLM reset the line should run freely for a day or so and then the DLM will intervene, this can reduce speeds or if options like lower noise margins kick in will speed you up, or G.INP can speed you up too.

One issue is that we have a big gap in the data from a year ago to three weeks ago, it may be that cross talk has been increasing i.e. result of more people taking the service and slowed your attainable down and possibly even slowed the sync speed down a bit, therefore it may be that current sync of 59 Mbps is a lot closer to what your sync was just before the fault.

The G.INP value of 3 on the current stats shows G.INP is off, and that can be worth a good chunk of speed and generally takes a week for the DLM to decide its fine to switch it back on.

NOTE: The switching off/on of the various elements can happen at anytime i.e. the 10 days to settle down is nothing of the sort since as conditions vary over time and the inputs to the DLM system change it will make its mind up based on the algorithms accordingly.

Thanks for your feedback. With respect to the big gap in data, I'm a bit of a sucker for visually checking these stats regularly on my router, and I'm 99.99% happy that there wasn't any creeping death around a month ago.

In reply to a post by MrSaffron:

10 day retrain - and I won millions on the lottery at the weekend, both are equally false.

BT say the same with FTTP as well, which makes me laugh, and you can argue that with them until you are blue in the face, so it just shows that BT Support have no clue what they are saying.

Paul

Ok - was worth mentioning.

The G.INP coming back on might be a 5 to 10 Mbps improvement so watch for the G.INP showing 48 in the stats, but should be obvious from the speeds you are getting.

Will G.INP increase my attainable rate, or just my rate?

Brain is not totally sure on the answer to that one as the modems I've had did not show the attainable

G.INP will increase both your rate and attainable but only if previously your line was interleaved.

Edited by deleted (Tue 12-Jun-18 11:42:54)

Thanks
Current settings for interleaver from router.

D (interleaver depth) 1137
I (interleaver block size in bytes) 64

My speed dropped suddenly about 6 weeks ago after almost 2 years of a solid 80/20 with 75 down and 19 up, the up speed is still the same,but the down is now 65, nothing else has changed in the stats, it almost as if the wick has been turned down at BT's end, at the same time BT started to offer me a new product which guarantees 100 down, maybe I am being cynical but BT won't look into the issue until the speed drops below 65,so is this an attempt to encourage me to move to the new product

Yeah, you're on Interleaving+INP. Once G.INP activates, you'll see a speed increase, hopefully back to where you were before the fault occurred.

Edited by deleted (Tue 12-Jun-18 15:29:42)

Finger crossed!

So, I should expect G.INP to reactivate given the stats I provided in the first post?

Eventually, yes. When it will, is unknown.

Edited by deleted (Tue 12-Jun-18 16:33:08)

I have a feeling holding one's breath isn't advised?

Naa, trust me, watching and waiting for it to happen just doesn't help or speed it up. XD

So, resync at 3am and looks like speed has boosted to 67705 with a max attainable still of 67767

G.INP has enabled, but still v disappointed my speed is way below the 79999 I had with a max attainable of 88000 prior to the fault.

Hoping for further improvements, I'm not convinced I'll see any now I'm hitting the max.

Link for stats image Stats 130618

Edited by deleted (Wed 13-Jun-18 09:36:53)

What noise margin did it re-sync at?

Current SNR Margin is 6.4 down

That's good. It suggests that it reconnected at 6dB when it was slightly noisy. Now G.INP is active it will (probably) be a couple of weeks or so before DLM decides to lower it to 5dB, then a few days to drop to 4dB then 3dB. Assuming the error rates don't prevent it.

Each 1dB drop gives well over 1Mbps more sync.

I've had a couple of spells where the first drop has happened on on the night when DSLStats is showing 23 days and a few hours since last sync.

As MrSaffron said earlier, we can't be certain you will ever get back your previous speed. It only takes one extra FTTC connection at the cabinet to take off anything up to 10Mbps due to crosstalk. It may be the first one after yours, or years later. It depends on many things, an important one being the proximity of the noisy line to yours on the route from cabinet to you.

It doesn't even need to be a "noisy" line as such, just a connection running close to yours gives crosstalk.

Edited by RobertoS (Wed 13-Jun-18 13:02:49)

Understood, but still massively frustrating

OK so had a resync this morning and the SNR margin dropped to 2.2 and my down rate is now back up to 79999. However, what's bizarre is that my max attainable rate is 69383.

Stats 260618

It will have sync'ed at 3dB at a low noise time. Now the noise has increased your margin has fallen.

Attainable is (in essence) continuously calculated by comparing the sync speed with the Noise Margin and working out what the speed would be if you had re-sync'ed again (which would be at 3dB) at the instant you read the stats. If you leave the modem refreshing that page you will see SNRM and attainable increasing or decreasing together.

If it doesn't auto-refresh every few seconds, refresh it yourself .

Many thanks for your help. Did a speedtest while wired directly to the Billion, and the results are:

Results

G.INP has been enabled on the Downstream as well.

Indeed. If only they would enable vectoring.....

Hi All

So my line is stable and back up to top speeds, so thanks for all your help

One question, I'm on an interleave of 16... will this drop or do other settings dictate this to be what it is (G.INP?)

Most recent router stats below

Stats

The normal level of interleaving when G.INP is active is 8. We do occasionally see a 16, and I dimly remember (perhaps) a 12.

It may or may not adjust down later, but it's nothing to worry about. Far better than being in the hundreds or thousands plus at least 8ms additional latency of non-G.INP .

Excellent, thanks. Xbox and most things show a latency around 29ms