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[ryan2390]

Hi All,

I know it seems daft given FTTP is coming very soon but I think I have an issue with my ADSL connection. If I recall correctly my SNR for a 5km line should be around 6dB but it's spent the last several weeks sat around the 1dB mark. Been trying to have a skype conversation this evening and I've managed to convince myself that it's the SNR causing the issues I'm having. My friend is on cable and not having any issues her end.

So my question is what should the SNR be? Even a rough estimate would be useful. Debating ringing BT to get them to reset the line profile. That usually puts the SNR back where it should be.

Cheers

Ryan

[burakkucat]

The target SNRM (target signal to noise ratio margin) for an average, normal, xDSL circuit can be considered to be 6 dB. However there are exceptions where the target SNRM is 3 dB.

The SNR is just the current "snapshot" of the ratio of the signal to noise and is varying, second by second. Most likely you are looking at the reported SNRM, the amount of "headroom" available for the constant changes in the SNR.

The simplest way of determining the target SNRM of a circuit is to force a resynchronisation event and promptly check the displayed SNRM and round it to the nearest integer.

[Weaver]

An SNRM snapshot that low, 1 dB downstream, is not good. It should be around 6, higher means it will be slow, lower is OK provided it does not go down to < 3 dB-ish. Really low numbers can means serious unreliability. This could mean that a change of settings or a different modem model is needed, or that there is a fault that needs fixing. Possibly the wiring up to the modem from the outside world needs sorting out. An Openreach SSFP (faceplate-type filter) and a Tandy / Adslnation RJ11 modem-to-wallsocket cable is needed.

[ryan2390]

Well I figured out how to get to my router's stability adjustment feature again and tweaked it about 3 or 4 times. Seemed OK but synced lower. turned it off and it's sitting around 6.6dB as I write this.

Would what I describe be responsible for what I can only describe as a hiccup? A very brief period of not being able to browse the web or in my case this evening having skype freeze? Now I've messed about with it it does seem to be behaving. Will see what happens.

Cheers for the assistance as always gents

[Weaver]

Would what I describe be responsible for what I can only describe as a hiccup? A very brief period of not being able to browse the web or in my case this evening having skype freeze?

Indeed it would. Exactly, Skype and streaming video services would be the first to fail. Web browsing and email might still work but would be unusably slow.

> Cheers for the assistance as always gents

You're very welcome !

[kitz]

I agree with weaver.    At 1db SNRm then you are most likely incurring quite a bit of packet loss.    You may be able to see these if your router displays the figures as CRCs .   As a rough guide, unless your line is very stable then dont let it go below 3dB.   

[ejs]

Doesn't it depend on the modem to a degree? I looked back at an earlier post from ryan2390 where they said they were using an Asus DSL-N55U and getting a remarkably high speed for the line length. If the target SNRM is 3 dB, then generally the current SNRM is going to drop below 3 dB at times (unless perhaps you connect at the worst possible time and stay connected). I suspect there may be a link between the high line rate and the lack of stability or large drop in SNRM.

I wouldn't say mine line is particularly good, but it's on a 3 dB target SNRM and I don't really think it's any worse for being on it. But then the SNRM on my line doesn't tend to vary by very much.

[ryan2390]

We have issues from time to time and this afternoon the router was showing -1.2 right up to the point it keeled over. Usually I just ring up BT and ask them to re-train the line and it works as it should. For the majority of the time I don't have that many issues. If the SNR value I see sits at 6 +/- 0.5db it's usually stable. I'm logged into an online game client 23hrs a day and that's usually a good indicator as to when it's not right as it lags or like this afternoon just gives up and disconnects.

We've had problems before with a card in the exchange so I wonder if that's the issue this time? I'm not sure what these first level folks can actually do. Like I say a line re-train seems to fix it. In a queue at the moment waiting to speak to them to see what they can do.

[Weaver]

Ejs wrote:
> I wouldn't say my line is particularly good, but it's on a 3 dB target SNRM and I don't really think it's any worse for being on it. But then the SNRM on my line doesn't tend to vary by very much

Same for me as for ejs. I have chosen to set my 21CN ADSL2 line to a 3 dB downstream target SNRM, and have been lucky enough to be able to get away with it extremely successfully. Currently, the d/s SNRM is 1.5 dB on the lowest one of these DLink DSL-320B-Z1 modems. Even as low as that sounds, it hasn't ever dropped lower than that, as far as I recall. The way these modems hang on in there and just keep going reminds me of my beloved Netgear DG834 v3.

[ Dull responsible public health warning: BlackSheep (and others) have quite rightly pointed out that you can't just be guaranteed to get away with this. It remains true that 6 dB target SNRM is a good choice unless you are lucky enough to have a low level of variability regarding line conditions, crosstalk and other noise sources. I was prepared for the 3 dB thing to be just an experiment and a failed one at that, and kept an eye on it on a regular basis. ]

Given that they have held up really well during the worst of the weather, that increases my confidence that it will be a keeper long-term, but you never know.