Low Noise Margin & frequent re-syncs

Hi All,
OK, I've been connected to NamesCo's HomeMAX 8Mb product for about a month now and am using the supplied (free) ZyXEL 660 router directly into the NTE5 master socket. The BT speedtester says that my IP profile is 5000kbps and I do get throughput rates up to just over 5000kbps on occasions (according to the NamesCo tester).

The router usually syncs at rates between 5000 and 6200kbps and sometimes reaches 6900kbps, with a downstream line attenuation of 44dB. I estimate the line length is around 3.2km. Note that the router is usually on 24/7.

The problem appears to be a noisy line. The router re-syncs often but the downstream noise margin tends to be between 4-8dB during the day and drops to 4dB and less at night. As the noise margin drops, so I get more frequent "connection failed" messages from the router whilst browsing the net. What I find strange is the sync rate pattern - it appears to drop to a low point around mid-evening then slowly increases throughout the night, so that the noise margin stays around 2 - 4dB. Trouble is, once the sync rate goes above 6000 the connection becomes unstable and above 6500 I can't open any web pages.

I thought the equipment at the exchange monitored line stability and set the appropriate noise margin (and thus the maximum sync rate).

Any suggestions for improving matters? By the way, I've disconnected the "ring wire" for the extension at the master socket, switched filters, tried the test socket, disconnected the phones and don't have a Sky box. I'm even plugging the router power supply into a noise suppressing power strip. Doesn't make any difference!

Cheers.

Steve

BT's design for MaxDSL assumes that the modem/router only resyncs if the margin is too low or the errors too high, so the behaviour you describe of the sync speed progressively increasing is going to cause instability.

If its doing that on its own I would be tempted to try a different device or to look into ways of stopping it (settings or firmware upgrade ?).

Hi Phil, thanks for the reply.

As I write this, the router is telling me the sync rate is 6214kbps and the downstream noise margin is 2dB and i'm finding that I'm often having to click on links several times to view new pages, etc.

Is it usual for the noise margin to vary so much? If it is, I was wondering if there's any way of setting a cap on the sync rate to increase the noise margin?

I believe the router firmware is the latest version. I agree it's worth trying another device. I've noticed that the DSL indicator light on the router "blinks" a lot - usually around every 10 seconds even when the connection seems stable. Anyone know if this is unusual?

Cheers.

Steve

OK Folks, an update...

Over the last week it would appear my target Noise Margin has risen from 6dB to 10dB. Am I correct in thinking the exchange equipment does this automatically?
Anyhow, I'm now syncing at around 5300kbps during the day but this drops to around 4300kbps in the evening and the Noise Margin still drops as low as 1dB and I'm still getting several re-syncs an evening....
Naturally, my IP Profile has dropped from 5000kbps to 4000kbps to 3500kbps as a result. Given the current sync pattern I would imagine that I'm not likely to see 3 days of higher rates which would raise my Profile.
Having read a number of similar posts on the various forums this week, it would appear to be a common issue. Various causes have been suggested (usually RFI based).
Could there be another factor? The weather has been pretty poor lately and I know that water can get into the BT ducts / Junction boxes. Is this likely to exacerbate the problem?
If this is not the case and my problem is RFI based, is there any point in asking the ISP to request BT check the line for poor connections - I've read some posts that stated replacing a dodgy interconnect has improved matters.

Anyone have any comments on this?

Steve.

Read this thread.......

http://bbs.adslguide.org.uk/showflat.php?Cat=&Board=technical&Number=2715201&page=2&view=collapsed&sb=5&o=0&fpart=

Yes, thanks for that.

I had read the thread previously and acknowledge the points you make are all too valid. I figured I did not have quite the same problem, as my line (AFAICT) is underground until it meets the junction box just above ground on the outside of the house. There is then only about 8 ft of wire to the master socket. The house is only 20 years old so the wiring should not be that bad!

I just can't figure out why there's no consistency in the variation of the Noise Margin on my line. This evening it has been varying from 0 - 11dB at both 5600kbps and 4600kbps sync rates. I suppose the router could be reading falsely, but at least it's consistent....

I presume that the reason the sync rate improves through the night (i.e. before 2am) is the Radio Stations shutting down?
I should add that I do get re-syncs during daylight hours (even with a 10dB Margin).

Even allowing for modulation of RFI signal strengths, aren't such large swings unusual?

Cheers.

Steve

If your lines as unstable as you have said you should be able to get your ISP to look in to raising an intermittent fault with BT Wholesale (they will of course double check diagnostics with you to ensure its nothing local that they can find).

Regardless of the speed changes the issue you should address with the ISP is the fact it drops off a lot in evenings and sometimes during the day, SNR and speed will change but BT's system from the sounds of it is unable to find a setting for your line to keep it stable.

BT do have teams who will attempt to locate local interference in your area if they are unable to find a fault with the copper but it is usually one of the last things to be tried as they are very specialised engineers.

Thanks for the reply Nathan.

Unbelievably, I've managed to stay synced at 4608 kbps for over 18 hrs now - despite the Noise Margin dropping to 0dB (again, according to the router stats...) - which is a record. Now, this could be coincidence, but I swapped the RJ11 cable that came with the router for one of those Belkin shielded affairs (out of desperation, really) yesterday evening. Perhaps the original cable was faulty - guess I'll have to wait and see!

Another thought is that the master socket is situated right next to some central heating pipes and quite near to the TV aerial socket. Surely, these couldn't be interfering with the line as well?? Any thoughts?

Much appreciated.

Steve