time between ADSL drops always a multiple of 60 seconds

Hi all,

Here's a really odd problem...

First, I should provide a bit of background. In November I reluctantly switched from Zen ADSL to Orange LLU, because here on the infamous LNPOP (Poplar) exchange any non-LLU speeds seem pretty much guaranteed to be dismally slow. (Whether that changes when FTTC finally arrives here next month remains to be seen ...)

From November to mid-January, the line was pretty stable albeit operating around 2-3Mbps, far below the estimated speed of 9Mbps provided during the sales process. However a few weeks ago, the line started dropping extremely frequently: sometimes up to 50 times a day, other times not even once a day.

I have both my Draytek VG2820n and Netgear N150 routers configured to send syslog messages to my desktop machine, so I have a precise record of when the line drops occurred. When I started doing some analysis on the last few days of drops, I noticed that the duration between drops was virtually always an almost exact multiple of 60 seconds. For example, in the last 2 days alone, the duration between drops was 660 seconds (plus/minus one or two seconds at most) on 21 occasions, it was 600 seconds on 17 occasions, 240 seconds on 12 occasions, 360 seconds on 8 occasions and so on.

This seems very peculiar to me, and I am wondering if it could provide a clue as to the cause of the drops. Surely these almost exact multiples of 60 seconds indicate that each drop is somehow correlated to the next, which would be impossible if the drops were simply caused by a faulty connection somewhere? It's also interesting to note that prior to the last few days, this pattern doesn't seem to occur, so maybe it's a new type of fault.

I'd love to know if anyone has ever seen anything like this before.

Thanks,
Adam

Or could simply be some code in the routers doing the following:

Start timer at 0 i.e. first time we resynced
8 seconds in oops some errors, correct them if we can (interleaving)
No errors for a few seconds
More errors
No errors
60 seconds have passed, how many errors in the last minute? Mmm a lot lets resync to try and resolve the issue

That had occurred to me, but how would it explain that for instance sometimes exactly 4 minutes pass between drops, and other times exactly 38 or even 55 minutes? If what you're proposing is the case, wouldn't it be more likely that there would be a fixed length between drops?

Why is it dropping - noise?

Because it might repeat that cycle every minute, and that the noise itself may be down to some device on a timer, or as regular as a train passing near by

Sadly no trains in this country are that predictable! What kind of device did you have in mind? I do not have any other devices connected to the phone circuit in my flat.

I think your suggestion of a repeated cycle in the router (or the DSLAM at the other end?) makes the most sense - in which case, wouldn't that make noise the most likely cause? i.e. noise which only sometimes exceeds the threshold that the router is willing to tolerate? If the drop was being triggered from the exchange side, presumably I would have noticed the same pattern when using my Vigor router - but I haven't.

That's what I'm trying to figure out! I have a fault raised with Orange but despite occasionally getting through to a good person on the fault management team, they've achieved zero progress in several weeks.

Anything that creates noise that can be picked up by an AM radio can potentially cause problems with ADSL

So I heard, I also saw http://www.kitz.co.uk/adsl/rein.htm but I don't have a portable AM/MW radio. Any recommendations for a cheap one which would serve well for this purpose?

Monitor using Routerstats or DMT.

Neither are compatible with my Netgear DGN150. Apparently I could use RouterStats-Lite with my Draytek VG2820n, but would it give me any metrics I don't already receive from the Draytek via syslog every five seconds? A typical log line gives me sync speeds, S:N ratio, and line attenuation e.g.:

Jan 10 03:04:23 vigor2820vn Vigor: ADSL_Status:[Mode=G.DMT States=SHOWTIME UpSpeed=608000 DownSpeed=3520000 SNR=12 Atten=47 ]

So I can already collect this data for analysis, but I'm not sure how that would help? Regardless of what I notice, isn't the noise on the line only fixable by BT/Orange engineers, who would always run their own diagnostics anyway rather than rely on the customer's personal analysis?

What he is after in one respect at least is the pattern of the noise variation and re-syncs, which RouterStats(Lite) graph very well as they keep going. DMT is useless for this as it stops at a disconnection.

If you can upload a graph of those from your logs that would be just as good.

Recently I've been using the DGN150 provided by Orange so that they can't complain about non-approved routers when they get me to run through their diagnostics. Unfortunately that router doesn't log useful metrics over syslog, only the precise time of the drop. I'll switch back to the Draytek and start collecting after they're done with their current investigations. But I've been keeping an eye on it, and generally every day falls into one of three categories:

1. no drops at all
2. drops all day long
3. drops only in the early morning, especially around 7am

Ultimately AFAICS from the OFCOM CoP, it should be the ISP's responsibility to figure out the problem and I shouldn't have to waste hours of my own time debugging it.

I do wonder if any of this could be related to the FTTC work that BT are supposedly finishing off right now in our area ...