Drop of Sync Speed from 20 Mb/s to 288 k !!

My mother in law moved ten months ago into a flat, next door to the local telephone exchange

Not surprisingly she had a sync speed of about 20 Mb/s.

About ten days ago the downstream speed started to slow, yesterday it had dropped to 576k. The noise margin has reciprocally increased, and was about 31dB.

Suspecting her router, I swapped it yesterday, for a spare one of mine. That kicked off at 576k
too, hoping that perhaps the the original router had been faulty, I was rather hoping the speed
would creep back up to 20 megs over the next few days, however within three hours the sync speed
dropped even further, it's now down to 288k.

Upstream has been unaffected throughout, about 1.1 to 1.2 Megs at 6dB margin.

What on earth is going on ? I've raised a ticket with PlusNet, no response yet.

If downstream noise margin is high and the sync speed still slow just after router has been rebooted, then suggests that the BT Wholesale DLM system has forced banding onto the connection in a very drastic manner in your case.

Does the router, show error stats too?

When you say "Next door ..." how close do you mean?

Can you get full stats including attenuation and errors. And an estimate of line length.

I dealt with one like this a few years back - basic ADSL or ADSLmax and it was the ultra short line causing problems.

In reply to a post by MHC:

When you say "Next door ..." how close do you mean?

Can you get full stats including attenuation and errors. And an estimate of line length.

I dealt with one like this a few years back - basic ADSL or ADSLmax and it was the ultra short line causing problems.

Distance as the crow flies about 200 metres

Router Stats:-


DSL Status: UP
DSL Modulation Mode: Auto
DSL Path Mode: INTERLEAVED
Downstream Rate: 284 Kbps
Upstream Rate: 1100 Kbps
Downstream Margin: 31 db
Upstream Margin: 6 db
Downstream Line Attenuation: 17
Upstream Line Attenuation: 15
Downstream Transmit Power: 15
Upstream Transmit Power: 11
LOS Errors: 0

PVC Connection

PVC Status: UP
Encapsulation: RFC 2364 PPPoA
Multiplexing: VC
Autodetect: Disable
VPI: 0
VCI: 38

Does her phone work?

In reply to a post by RobertoS:

Does her phone work?

Yep, clear audio and no audible noise on the line

If it was a noisy line problem, I'd expect a noise margin of 6dB (or lower) ?

Edited by broadbandjockey (Wed 11-Jun-14 11:17:13)

That rules out my thoughts - the one I dealt with had a line length of under 20 metres. At over 200m it would not be relevant.

I was thinking of one wire off.