Latency hike after BT business fix connection drop problem

I've got BT Business broadband on a plain old non-fibre ADSL connection, using a Draytek Vigor 130 modem and a linux PC router.

Everything had been fine for some time but 48 hours go, the connection kept dropping repeatedly for 20mins or an hour at a time. The problem would go away and then seemingly randomly come back.

I checked out the Draytek Vigor modem which showed 8000+ RX CRC errors since I had rebooted everything when it first started playing up.

I logged onto the BT Business website and tried running the self-service diagnostics test, which involves logging a fault, but the test failed 2 or 3 times.

I gave up for the day after that, but discovered this morning that a BT engineer had picked up the logged fault ticket and sorted out the connection dropping.

I run smokeping on the linux router, and it shows that the latency has jumped from 9ms to my test target host, to 24ms.

My speed hasn't changed from 12/7 before and after.

I am curious what BT did, and whether I caused or could influence the issue next time, and whether I can do anything to bring down the latency to 9ms again.

Edited by TreeHugger (Wed 24-Jul-19 13:24:28)

Turned on interleaving error correction

24ms on ADSL is still well above the expected average

In reply to a post by MrSaffron:

Turned on interleaving error correction

24ms on ADSL is still well above the expected average

I tried. The Draytek Vigor 130 modem has a DSL mode 'auto' option, with which it says "Physical mode: ADSL".

I changed the mode option to VDSL but then I couldn't get the linux ppp module to connect, it fails with

Timeout waiting for PADO packets
Unable to complete PPPoE Discovery

So I had to set the modem DSL mode back to auto. To tell the truth I don't really know what it's doing.

The Draytek website shows some modem config options which aren't showing on my modem's GUI so I think the firmware is a bit different.

Investigating further it looks like I'm on a BT specific firmware - the firmware version is 3.8.1_BT even though I bought this from broadbandbuyer.com.

I'm not sure about updating the firmware with the latest version off the draytek website since I expect I wouldn't be able to go back to the 3.8.1_BT firmware if I wanted to roll back - although it does look like it might be worth a try since the website now offers v 3.8.4 (but no BT specific version in sight)

Still investigating.

Unless you have a VDSL2 service any modem will not connect it, and if you have VDSL2 the modem won't connect using ADSL

So not sure what you are investigating now.

Interleaving has been turned on by the DLM in the exchange to reduce the errors. You can't do anything at your end to remove it. If the line stays stable it may be removed again.

In reply to a post by MrSaffron:

Unless you have a VDSL2 service any modem will not connect it, and if you have VDSL2 the modem won't connect using ADSL

So not sure what you are investigating now.

Hmm, goes to show the extent of my knowledge about broadband. So VDSL is cable or fibre or something?

VDSL2 is part of the DSL family

ADSL/ADSL2+ and VDSL2 use different frequency bands and need different hardware in the exchange for ADSL and in a street cabinet for VDSL2

In reply to a post by TreeHugger:

Hmm, goes to show the extent of my knowledge about broadband. So VDSL is cable or fibre or something?

VDSL or, more specifically VDSL2, is FTTC (Fibre To The local street Cabinet). Copper from there to the premises.

If you want to brush up on your knowledge, Kitz is a great site with a wealth of info:
https://kitz.co.uk/adsl/fttc.htm

Thanks for the info. It seems that BT have put some sort of sticking plaster on my connection then in the hope that it will improve of its own accord.

There was no communication from BT about this. It could just get worse again instead of improving.

I see the latency dropped last night at 23:00 from 24ms to 19ms, but at 2:00AM there was a connection drop, and it reconnected with 24ms latency again.

The same thing happened again at around 7:30AM, it lasted 4 hours before dropping out and reconnecting with 24ms latency again.

Is this automated connection management then?

Very possibly the DLM (Dynamic Line Management)

Interleaving: https://kitz.co.uk/adsl/interleaving.htm
DLM: https://kitz.co.uk/adsl/DLM.htm

Is your business dealing with gaming because 24ms seems quite good?