Seasonal ADSL retraining: Interleaves on the line?

While I was away at the RIPE 65 meeting in Amsterdam last week, my home DSL went down. I suspected that the router and the exchange equipment had got into some crazy state where packets are massively errored, but sync isn’t lost, so there’s no retraining. The only way of recovering is to bounce the adsl interface on the router, either in software, or unplugging from the phone line. Occasionally, since moving, this happens, and seems to be related to the weather, which had been very wet and windy at the start of the week.

Since moving, I live toward the edge of the coverage of my exchange, the line length is estimated to be about 4km, and it has to get across a EM noise ridden town centre and an electrified railway line or two to get here. Both of which are potential factors that influence one’s line speed. It’s delivered overhead from the nearby pole on a dropwire, while the rest is UG, though that shouldn’t have any significant issue.

Initially, syncing at around 5Mb with Interleaving, but retraining several times a day the line eventually settled down to run stable without Interleave at around the 3Mbit mark, which is okay for most things other than TV streaming, but we’re not a Netflix kind of household, so don’t really mind.

My unfailingly patient girlfriend (who also needed to use the internet connection) reset the line, things retrained, and we were off again.

However, when I got home, I found the performance seemed a bit slow, so I checked the router. The line speed had dropped to sub 2.5Mb/sec, with Interleave on.

After a couple of retrains over the last few days, the speed has crept back up and following an “invasive line test” via BT.com, which forces a drop and regotiate it’s now syncing again at 3M, but still with Interleave – which is no great loss to me as I’m not a huge online gamer these days.

(Now realising that’s a way of forcing a remote reset when it’s got into a heavily errored state but hasn’t lost sync. Handy when I’m away and there’s no-one in to pull the plug.)

So, this is not the first time I’ve had fun with the line since moving. During the recent spell of hot weather, things would run fine until there was a sudden cooling, such as rapid cloud cover or a heavy shower, at which point the connection would drop and need to be nudged to renegotiate.

It’s got me wondering if the line is affected by a dry joint or degraded cable somewhere along the way.

Doing a ‘17070’ and quiet line test, it’s got a faint “shushing” noise, rather than total silence, and I did just notice what seemed to be “crosstalk” of ringing current (a faint “click-click, click-click”) for a few seconds.

Not sure whether to argue the toss with BT to get them out to give the line the once over (but risk having an indifferent BTO engineer make it worse rather than better), or just give in and go FTTC, despite the fact I’m 3 months into a 1 yr tenancy and FTTC has 1 yr minimum term and can’t cope with you moving house (yet!).

Update, 5/10/12:

Had a chat with my old man about this. He’s a retired BT engineer, so generally knows his stuff about copper plant. Agreed with the likelihood of it being a dry joint and/or the possibility of their being other dry joints in the same cab/DP with a shared earth, given that the “click-click” of ringing current is sometimes audible over a quiet line test.

His suggestion: Phone BT until they are sick to death of you and keep asking for either the joints on your existing routing to be re-made, or a new routing to be provided.

4 thoughts on “Seasonal ADSL retraining: Interleaves on the line?”

  1. Interesting experience. Way less frustrating then what you can have in India with BSNL! 🙂

    Here lines are usually short less then 3km mostly because there’s next exchange within that range in most of cases. But issue goes to excessive joints and quite of them are open ones being effected by rain & moisture.

    Btw what exactly is “max speed” there? Does that really means achiveable speed? If yes then based on what?

    My connection stats:

    Downstream Upstream
    SNR Margin
    :
    35.7 12.2 db
    Line Attenuation
    :
    18.3 13.0 db
    Data Rate
    :
    1999 836 kbps
    Max Rate
    :
    22564 1054 kbps
    CRC
    :
    2 0

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