After a long time with tech support, they've now confirmed I *am* on ADSL2+ and the chat about things being oversubscribed was nonsense.

However, they're telling me I have 46dB attenuation and a line length of a smidge over 2km. They've got my line set to 10mbps, but it's only syncing at 5mbps "because of this line length."

Seems odd to me again; surely a longer line would just result in increased attenuation, and if the signal attenuation's at a certain level and the line's clean without too much noise, you should get a speed based on that?

Perhaps the 5mbps cap I have now (according to MySky) is left over from when I was on G.dmt?

The problem is the noise on your line

Noise Margin 6.1 dB

All phone devices must be filtered, including the sky box.

You should get your stats from the test socket behind the master, with *nothing* else connected and see what happens to the noise figure.

Do you have a test socket?

I do; those stats are from the test socket with nothing else connected.

Todays stats, from the test socket but with the phone connected, are:

ADSL Link Downstream Upstream
Connection Speed 4916 kbps 796 kbps
Line Attenuation 45.5 dB 27.4 dB
Noise Margin 7.0 dB 13.8 dB

Edited by deleted (Sun 12-Jun-11 14:16:48)

5220kbps would be an unusual cap (and I don't think you're on a cap) as it's not really a natural step (it's more than 5Mbps but less than 5.5Mbps and I'd assume any implemented steps would go 0.5, 1, 1.5, etc).

I suggest you try the usual DIY checks as your line should do more than 5220kbps at the 6dB margin (but not that much more - I'd expect somewhere around 7 to 9Mbps).
Try the 'test' socket (INSIDE your BT master socket) to rule out any internal wiring "issues" and post your stats again.

You are correct about the line speed being determined by the noise (your modem & exchange will attempt to sync with the highest possible number of 'tones' which can meet the 6dB target margin).
However the line attenuation also plays a part (the modem won't say "OK; the attenuation is xx so I'll connect at yy") as the higher frequencies (and thus the higher speeds) will not make it through.

If you were being capped (at 5220kbps) you would almost certainly see a higher downstream margin.
The fact it's at 6dB tends to imply your modem has selected the sync speed based on the noise level rather than being forced to connect no higher than 5220kbps.

5220kbps certainly won't be a cap left over from G.dmt (aka ADSL1) as 5220kbps is an impossible connection speed for that modulation (5216kbps is a possible G.dmt sync, as is 5248kbps; but it can't go in between).

In reply to a post by Elmlea:

I do; those stats are from the test socket with nothing else connected.

Then you have a noisy line and there's nothing you can do about it (unless you get hissing or crackling on the phone line).

From the test socket with nothing else connected:

ADSL Link Downstream Upstream
Connection Speed 4898 kbps 796 kbps
Line Attenuation 46.0 dB 27.4 dB
Noise Margin 7.4 dB 14.0 dB

From Sky's site:

Download Speed
Your connection has been set to a download speed of up to
4.9Mb (5024Kb)
Upload Speed
Your connection has been set to an upload speed of up to
0.8Mb (800Kb)

It was the "connection has been set to" bit that made me think it might be capped. Also, there's a lot of space left upstream before it's anywhere near 7dB noise margin, so at least I could expect an improved upload?

The fact your download and upload connection speeds are jumping about all over the place lends me to believe you have a line fault (possibly just a dodgy joint somewhere between your master socket and Sky's equipment in the exchange).

The "set to" part (I think you mentioned 10Mbps) may just be a measure by Sky to reduce connection issues on longer lines (if they've capped you at 10Mbps). Of course it could equally be number 47 on the list of 'rubbish answers to make you go away' at the call centre!
The thing is you're getting nowhere near that and it's all pointing at a line fault.

A line fault, rather than just an unfortunately noisy line?

I'm not sure why, but at one point they managed to creep the downstream up to a steady 5200kbps, but at the same time the upstream fell to 412kbps. Other than that it's been relatively static.

Presumably that's when they tried g.dmt.

I think Sky are starting to get a little naughty and despite their promise not to over subscribe lines like other providers, they are. If people do not complain, hey great we can out a few more customers on the line. Was upgraded to adsl2+ last Feb, and after a while speed went down to 1.3mb instead of the 5 i was getting. Support guy told me I should only be receiving upto 2mb anyway (yea right...it will be 56k next). When I strarted a little rant about promises and oversubscribing, guy went away (flicked a switch?) and 2 minutes later hey im back at 5mb with a guantee that it will not fall in speed again as he has put a note on it??? A note on what and to not do what exactly?