is the calculator actually working properly? i think it only says 'very good' for adsl2+ with a low attenuation if one enters Downstream Connection Speed (Kilo bits per second) as 200000 (one zero too many)

i'm entering the following details:

Connection Type: ADSL2+
Downstream Connection Speed (Kilo bits per second): 20900
Downstream Attenuation(dB): 5
Downstream Noise Margin/SNR (dB): 9

and getting the following result:

Estimated connection speed using ADSL2+ mode (maximum 24 Mbps)
Red traffic light, actual speed is low
Bad
Normal speed range at 5dB attenuation is 21500 Kbps to 21500 Kbps
Target Margin Estimate
9dB 20900
6dB 22800
3dB 2280000

Noise Margin 13.4 dB 15.0 dB

NOSIE MARGIN 13.4 DB. INDICATES THAT YOU CAN GET BETTER SPEEDS....

Router wise, that router has pretty poor wireless that barely covers any range. ADSL wise it's not great at getting a good sync either.
There are much much worse ones out there though. So overall it's not too bad.

I'd personally try out a NETGEAR DG834 V3 or a speedtouch 585 as both are good at holding sync. The netgear gets better speeds but the speedtouch is more stable in experience.

You don't need anything with fancy wifi as the speeds already so slow.

TBH though you can get better speeds with the current router. There's no guarantees an alternative router would be ANY better. I would personally try to get that noise margin down to 6db which means figuring out why it's so high. Soo take this course of action before spending dollor.

Edited by ukhardy07 (Thu 13-Sep-12 19:08:30)

Why is the nosie margin so high?

Something's causing it. Could be a faulty sky box, lamp-post outside, poor internal wiring, unfiltered extension, etc etc...

I edited my response slightly. The key thing here is to find what's causing the high SNR rather than spending money on routers.

It seems given the op's original post that they're experiencing some instability even with this high SNR which is never good.

We did that - plugged router into test socket, stats unchanged.
I think the line speed is capped.

I wouldn't say 'capped.'
I would say on purposely restricted due to some noise / error build up. Generally things only get capped because of an issue somewhere.

a 13db noise margin is ever so weird though - especially after a resync. I expected 12 or 15db after a resync but all of the stats have been around 13db. This points more towards a cap on the sync and not a noise margin increase due to instability.

No mention of who the ISP is that I can see.

TEST socket isn't always the full story. PLENTY of times I've found that some extensions still work even when the faceplate is removed. So many houses have star wiring and a master stuck on randomly somewhere. Definitely worth a consideration.

Not only this but REIN or just poor quality wiring / a very long line from the exchange can often mean a 6db noise margin isn't stable (and this is beyond the users control).

Anyho, I'll stop butting in as much as possible.

Edited by ukhardy07 (Thu 13-Sep-12 19:26:26)

Very good points, well worth thinking about (except the last).

Why not the last?

It's very likely given the users line length that the reason for the higher noise margin is not inside their property. Longer lines often have much 'flappier' noise margins and therefore need higher target noise margins to remain stable without drop outs.

A longer line = more suseptable to outside interference and more likely to pass something which emits some kind of REIN.

Also the cabling may all not be underground which can have an impact.

The wiring outside is very important in my opinion. It's definitely worth thinking about. Given that they have tried the TEST socket, if this is wired up correctly & does disconnect all extensions then it does point to outside the property which is beyond their control.

Edited by ukhardy07 (Thu 13-Sep-12 19:33:38)

Line looks like a 20CN line, so 1216 is not a valid cap speed.

What seems likely is that DLM saw some instability and raised target margin to 12dB. The router may have contributed and possible previous wiring issues.

So if ISP can reset target noise margin to 6dB, you should see better speeds, whether they will be stable is anyones guess. As for best hardware, it is very much experiment to see which cope with the line length (which is 5.5km or more, not 4.5km as one said) and also the various local noise sources.

Overhead cabling if twisted pair generally has very little impact, and if it was that as constant noise you would be seeing a 6dB target and the same sync.

The calculator gives that result because ADSL2+ should really sync at around 21500 or faster on a line that is probably just 100m from the telephone exchange to the home.