Should I expected better speeds with these stats?

[plummet]

Hi

I have BT business broadband on a dedicated business line. The setup is as simple as you could get - microfilter into the master socket, then straight into a Netgear DG834v2 router running the latest firmware.

I'm typically seeing:

Line attentuation down: 37db

Noise margin: from a long plot, seems to be around 9 during the day, around 7 at night

Connection speed: currently a dismal 736Kbps down

From the line attentuation figure, based on some graphs I have seen I would expect far better connection speeds - maybe as much as 13Mbps. A neighbour gets 5Mbps and used to get 8Mbps.

So, is the issue the noise margin? I still don't quite get whether this means the amount of additional noise that can be accepted before the modem switches to a slower speed (in which case the higher the better), or whether it is the amount of noise on the line (in which case the lower the better).

Would it be worth trying a different router?

Thanks for any help!

[MHC]

Typically a router will sync to give a noise margin of 6dB.   If the margin is above 6dB then you could resync  and obtain a little more speed.  But if the margin is lower than 6dB (and how much depends on the modem) can result in a resync back to a 6dB target.

You are well down on speed, and I would have thought that you would be up at around 10Mb based on your attenuation figures.

If you neighbour has dropped from 8Mbps to 5Mbps and your speeds are low then my gut feel is that you lines are picking up excessive noise or interference which could be inside the house or from a source in the street.

Have you tried taking the lower half of the face plate off the socket and plugging your modem into there - you may need a BT to RJ11 adapter, but it will prove whether teh problem is in te wiring on BTs side or yours.

Do you have the BT supplied 2700HGV that you can try too?    It has one of the best modem front ends on the market.

Also, have you downloaded RouterStats Lite and used that to plot your SNR and sync speed over 24 hours?

If you want some further assistance, send me a PM

[plummet]

Thanks for the reply - the noise margin thing makes more sense to me now.

Yes, I tried connecting directly to the test socket, didn't make any difference. I don't have any extension wiring connected to the socket anyway, in fact I don't even have a phone plugged into it as the business line is used for broadband only (it is enabled for telephone calls, but I don't use that line for that). So, just microfilter and then straight into the modem. I also tried without microfilter - no good either.

Tried the 2700HGV and it couldn't even sync! I could see it trying to negotiate but then it failed. BT are going to send me a newer version - frankly I think that has no chance of helping but maybe excluding that will let them take the investigation further.

I did take a router stats plot (but didn't save it). The LA is fairly constant, but the noise margin goes up and down quite a bit. One odd thing is that for a few hours last night the noise margin went up and then the modem synced at 2.5Mbps. The actual download speed was still pegged low due to the low IP profile, but I was hopeful it would have gone up by the morning. In fact, by the morning the modem had synced down to 160kbps again...

I agree it sounds like a noise issue. I wonder if it is significant that the residential line comes into the house in the same physical wire - it is a 2-pair coming from the street (1 pair residential, 1 pair business). I'm not particularly impressed that they split out the pair for the business line within the residential master socket and then run it back out of the house again round to where the business line comes in. Would have made more sense to me to branch it out at the junction box on the wall of the house to save a few meters of cable and a few fiddly connections - but the wiring is correct and I don't know if it would introduce that much noise.

I also tried the MW radio trick I read about to listen for internal noise sources. My LCD panel absolutely howls, as does a laptop power supply, but I moved the router to be well away from those and I don't see an improvement. So, I guess it must be noise somewhere further down the line...could be fun trying to get BT to look into that. Maybe they have a way of measuring line noise from the pavement connection to really exclude it from being anything to do with my setup.

Tony

[plummet]

...one more observation, I just plugged a telephone in to check the line sounds quiet, and the sync speed shot straight up to 3.5Mbps!

Maybe a coincidence, but on the face of it looks like having a phone plugged in to the microfilter as well as the DSL connection is somehow improving the situation, compared to just having the DSL into the microfilter and the phone unconnected.

[MHC]

What is the voice quality like on the 'phone?    Good, bad, noisy?  

Terminating the circuit with a phone can have a small effect, but the effect on yours is quite marked.    Leave the phone in place and monitor teh sync for a day or two.   It can take two or three days for your IP profile to change - see what happens with that.

RouterStats Lite does says images on a regular basis - they may be there.

[plummet]

Initially I thought the voice quality was good, but with another quiet line test I do occasionally hear clicks and whistles.

From some more experimentation, the difference when going off hook is no coincidence - it makes a marked difference every time.

I did some Googling and it sounds very much like a high resistance fault - where the extra current drawn by going off hook causing a sealing effect allowing better transmission of the ADSL signal. I passed this onto BT and they are sending an engineer out this week (they've been very helpful) so I'll post the outcome back on this thread in case it is of use to others.

[plummet · Accepted solution]

Just to close the loop in case it is of interest to others, the problem was noise on the line due to a dodgy connection somewhere between me and the exchange. So, the engineer swapped the line with the residential line. I'm now getting a healthier 7Mbps.

That said, now I have a crackly residential line...another call to BT for that one!