8900AX-2400 S/N continuosly drops over time

[ardsar]

After monitoring the line stats for almost a day, I am worried to see that the handling of the bit/tone allocation on noisy lines is constantly reducing. I had exactly the same issue with the Netgear D7000 and after 3 months had to return it. Netgear stated it was a broadcomm issue. I was hoping this unit would have behaved like the 880AXL.....

In the evenings, S/N starts to drop due to increased interference on the line. This results in higher bitswapping and re-allocation of which bins are used. It would appear (like the D7000 does) at some point that the bins are marked unusable hence when the interference reduces, the S/N stays low. Over time, this eats away at the S/N.

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[gatekeeper]

My understanding is that there is always a certain degree of swapping of the tones going on, on any given line, and that this is all part of the mechanism to render the best error rate. That's to say, higher order tones can be substituted by lower ones, and vice versa.

Overnight and at other times when either adjacent lines of the copper loop are in heavy use and when also AM band interference has an effect, one would also expect to see the SNR of the line going slightly positive (downward, towards zero), as this would be saying that noise margin is being reduced due to the presence of the noise. For instance, in my case where I'm on ADSL and am operating at a target SNR of 15dB, I see my instantaneous or spot SNR dropping to 14dB, or sometimes as much as 12dB overnight. I think that 12dB is just sufficient to keep out the greatest degree of noise on my line. We can see that, in your case, it's going positive (I use that term rather than 'dropping' because it's less ambiguous) by about 2.5dB, which may or may not be normal for VDSL. But I can't comment any further, as to date I've no hands-on experience of VDSL.

Looked at in one way, though, this is beneficial, since the movement in SNR is at the same time increasing your down-direction sync speed, isn't it? It depends on whether this is now giving you some particular problem or not, or whether the SNR see-saws like this day in day out. If your copper loop happens to be particularly long - say, over 800 metres - and is normally subject to a lot of external impulsive noise or a lot of additional crosstalk in the evenings, then you might have a bit of a problem because the 8900 might then decide to always re-sync after a while, and obviously you don't want that to happen in any cyclic manner. I wonder therefore whether this could be due simply to you using VDSL on what happens to be a long local loop. I don't think you've mentioned how long it is.

I don't know whether, with VDSL, it's ever possible to get BT Openreach to force a new target SNR for your line, if what I assume about your line length is true. Them setting a new target SNR of, say, 12dB (or even higher) would give your line considerably more noise margin, so even if the SNR drifted down (in the direction of zero) it'd be of no consequence. It's a pity you can't experiment with a different target SNR yourself, but unfortunately that's not made available on VDSL, only on ADSL. You doubtless know that already.

I suspect you're up against the characteristics of your particular line here, and of the way in which VDSL works in default state. I somehow doubt that this is the fault of the 8900.

I think that unless someone in these Billion forums can enlighten us further, your best bet would be to present this scenario in the FTTC forum on thinkbroadband.com. They have some really good ADSL/VDSL experts on that website and I feel sure you'd get some useful comments from them, at the very least.

[billion_fan]

After monitoring the line stats for almost a day, I am worried to see that the handling of the bit/tone allocation on noisy lines is constantly reducing. I had exactly the same issue with the Netgear D7000 and after 3 months had to return it. Netgear stated it was a broadcomm issue. I was hoping this unit would have behaved like the 880AXL.....

In the evenings, S/N starts to drop due to increased interference on the line. This results in higher bitswapping and re-allocation of which bins are used. It would appear (like the D7000 does) at some point that the bins are marked unusable hence when the interference reduces, the S/N stays low. Over time, this eats away at the S/N.

before.png

After.png

S_N.png

What firmware version are on??

[ardsar]

@ gatekeeper. Think you miss understand - if i leave the router powered up the S/N will continue to drop. As stated in availability thread, this device behaves differently to the HG612, HH5a and billion 8800AXL - all of which see a 1 dB drop in S/N at night, but recovers the next day when the noise has gone. With the 8900AX it NEVER recovers the lost S/N.

The firmware is the one that was shipped with the product - same as what is available on line.

[gatekeeper]

Apologies. Yes, it looks like I didn't fully understand your issue.

Are you really saying, then, that the SNR will continue to drop every single night, going further and further towards 0dB? Or have I still not fully understood? If the answer to the first is Yes, then I can see that within just a couple of days or more the device will become unusable. Jeeez, that's bad.

I can understand why billion_fan is asking you which firmware you're using. Looks like this is a problem that only Billion themselves will be able to address.

Frankly, it sounds quite alarming for a VDSL router to be behaving like this (assuming it is the router and not instead something to do with the DSLAM at the cabinet). I'm especially interested, as I've been intending to get an 8900AX - however, not until and unless all basic bugs have been ironed out.

As far as I can see, nobody else who's bought an 8900AX recently is reporting the same behaviour.

[billion_fan]

Apologies. Yes, it looks like I didn't fully understand your issue.

Are you really saying, then, that the SNR will continue to drop every single night, going further and further towards 0dB? Or have I still not fully understood? If the answer to the first is Yes, then I can see that within just a couple of days or more the device will become unusable. Jeeez, that's bad.

I can understand why billion_fan is asking you which firmware you're using. Looks like this is a problem that only Billion themselves will be able to address.

Frankly, it sounds quite alarming for a VDSL router to be behaving like this (assuming it is the router and not instead something to do with the DSLAM at the cabinet). I'm especially interested, as I've been intending to get an 8900AX - however, not until and unless all basic bugs have been ironed out.

As far as I can see, nobody else who's bought an 8900AX recently is reporting the same behaviour.

If the issue also occurs the D700, then mostly likely related to Broadcom, (we can't write the DSL/PHY code, only Broadcom control this)

[gatekeeper]

Frogfoot, in his/her "Initial impressions of 8900AX-2400", seemed to think the device worked just fine, apart from a snag with DHCP. And at broadbandbuyer there's now a customer review by Mark W, in which he says that his 8900AX-2400 works admirably and that he can't fault it, really. He even compares it to the Netgear D7000, reckoning that the 8900AX is the better of the two. Have they completely missed the 'falling SNR' bug? Hmm, perhaps they have!

[billion_fan]

Frogfoot, in his/her "Initial impressions of 8900AX-2400", seemed to think the device worked just fine, apart from a snag with DHCP. And at broadbandbuyer there's now a customer review by Mark W, in which he says that his 8900AX-2400 works admirably and that he can't fault it, really. He even compares it to the Netgear D7000, reckoning that the 8900AX is the better of the two. Have they completely missed the 'falling SNR' bug? Hmm, perhaps they have!

At the moment it only effects ardsar line (this is not only just a billion issue on his line, it is a netgear issue also if two different devices, manufactured by two different companies experience the same issue, what does tell you??)

Remember all lines are different depending on cabs, environment, interference, lines, length etc, so routers will react differently to each line they are deployed on (so ardsar might have this issue, but others don't)

As no one else has this issue, its safe to say the 8900AX is working as expected for many. (remember we are using the latest PHY code released by Broadcom, we can only work with what they have provided, Broadcom is the best chipset for DSL lines, from my experience, they can hold a low SNR without dropping out unlike other chipsets)

[gatekeeper]

Billion_fan,

To a large degree, I'm with you on that. For many years now I've appreciated the benefits of using routers equipped with, specifically, Broadcom chipsets, and that's mainly why I've always bought and used Billion routers.

Although all lines are different, surely in the end it's the cabinet DSLAM and the user's modem (sometimes with manual control of the SNR) that decide on just how good or bad the line's running and they subsequently set the target SNR and the line speed accordingly? To my mind, it'd be a bizarre situation therefore if the SNR behaved in the way that ardsar is showing us. Not that I'm disbelieving him; after all, he seems a very technically-capable person. From my point of view, I'm wondering whether he's ever left the 8900 long enough to see what happens to the line ultimately. For instance, does the SNR go right down to 0dB, then revert to 9dB, and the process start all over again, or does the router just accumulate vast numbers of line errors and simply stops all communication with the DSLAM?

There could be all manner of possible reasons why this is happening with ardsar's 8900. But we're not privy to exactly how he's using it, including whether or not the application he's using to monitor the performance might itself be at fault. (Any sensible engineer would begin suspecting such things). But there again, he has seen (so he tells us) the same phenomenon on a D7000, so I'm inclined to think that he has indeed found an important and common bug to the two.

I just googled Broadcom to see if, at any of their websites, there was any easy means to contact them. There isn't, as far as I can see, no matter which branch of their sites around the world you pick. So maybe this is something that Billion will have to take up with Broadcom instead?

To corroborate ardsar's discovery (or not, as the case may be), others who've recently bought the 8900AX could perhaps be persuaded to manually monitor their line SNR's via the normal GUI for a week or so on a daily basis and report back to this forum as to whether they've observed the same thing happening?

[mognog]

Well I don't know where abouts a graphical version of the SNR is on the Billion 8900AX-2400 router but I do know I can see (what appears to be) the current value under Status-->Statistics-->xDSL

I'm using Sky Fibre with my router set in all in one mode (I'm not using the Open reach modem).

The router has been up and running for 18 days now and all is working just Dandy although I've not been monitoring if SNR has been going down

PS: I'm a software developer (of 30 years) by trade - not a router specialist but I do like fiddling with gadgets and things

SNR.png

My software version is the one it came with which is 2.50a.d32

I think the B0 Line rates show what speed the router is getting - 74 Mbps down and 20 Mbps up.