DSL Diary – 23/10/2012

Latest instalment…

Currently away at the NANOG meeting in Dallas. Got an alert from the RIPE Atlas system that my Atlas probe had become unreachable.

Bit of testing from the outside world showed serious packet loss, and nothing on the home network was actually reachable with anything other than very small pings. I’d guessed the line had got into one of it’s seriously errored modes again, but thought I’d try leaving it overnight to see if it cleared itself up. Which it didn’t.

So, how did I get around this, and reset the line, given that by now my tolerant girlfriend would be at work, and couldn’t go into the “internet cupboard” and unplug some wires?

Well, turns out that you get BT to do an invasive test on a line using this tool on bt.com. This has the effect of dropping any calls on the line and resetting.

The line re-negotiated, and came back up with the same speed as before, 3Mb/sec down, 0.45Mb/sec up, no interleave.

Looking at the router log, the VirtualAccess interface state was bouncing up and down during the errored period, so the errors are bad enough to make the PPP session fail and restart (again and again), but the physical layer wasn’t picking this up and renegotiating.

Of course, BT’s test says “No fault found”. In terms of the weather in London, it has been damp and foggy, further fuelling the dry joint theory.

I’ve also had a chat with Mirjam Kuehne from RIPE Labs about seeing if it’s possible to make the Atlas probe’s hardware uptime visible, as well as the “reachability-based” uptime metric. They are looking in to it.

DSL Diary – 18/10/12

You may have read my post regarding a spell of degradation on my home internet access – Interleaves on the Line?

The other recent addition to my home network is a RIPE Atlas probe – this is part of a large scale internet measurement project being run by the RIPE NCC. One of the advantages of hosting a probe is that you get access to the measurements running from your probe, and you can also get the collection platform to email you if your probe becomes unreachable for a long period.

As it turned out, my probe appeared to be down for half an hour last night, but I know I was using the internet connection just fine at that time, so maybe I’ll put that down to interruption between the probe and the collection apparatus?

Well, the current status is that the line has been up for seven days now, at just over 3Mb/sec, Interleaving off.

Still not the fastest connection, but at least it now seems to be more stable.

One thing I’ll keep my eye open for is if the line goes back to Interleaved, as the Atlas probe should show up the difference in latency that you get with Interleaving enabled.

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.