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Standard User meditator
(fountain of knowledge) Sat 19-Jan-19 14:04:54
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Can DLM sometimes fail to work at all?


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Can Dynamic Line Management, which I understand, rightly or wrongly, as being constantly exercised by the DSLAM, sometimes fail to function at all? Have there been cases of poor or non-existent DLM reported on particular DSLAMs?

For a few years now I've had a 40M/10M FTTC broadband account with IDnet and using a Billion 8800NL router, and all has been well with it in that period. But recently I invested in a more fuller-featured Billion router, the 8900AX-2400, only to discover that the power output on upstream is now abysmally low (2.8dBm) and consequently upstream rate has dropped from the very respectable 8.2M bps to 6.7M bps. Whilst I've anticipated a dip in rates due to the mere fact of physically doing the router swap and of restarting the 8900AX a couple of times, there's subsequently been no sign whatever, in over a month, of the upstream rate recovering upwardly. It's as though there's no DLM at work. Meanwhile, downstream rate is the same as previously, being 39.9M bps (so, no issue with the downstream side of things).

Both routers have, in their respective usages, exhibited totally stable performances, the only real difference, stats-wise, between them being that, with the 8900AX now, there are far more line errors on upstream. My premises internal wiring/filtering has always been second-to-none, nothing has changed physically with any part of the line back to the DSLAM, the 8900AX has been configured in exactly the same way as was with the 8800NL, but in over a month now DLM has failed to restore the upstream rate to anything like it was before. In fact, upstream rate plummeted on the changeover and has simply stayed like that. Of course, each time I try resync'ing the line I lose yet more upstream rate (though downstream rate stays at the 39.9M bps figure). But each new upstream rate gets stuck at its value and shows no sign of migrating back upward, even after weeks and weeks of waiting. It's plain that if I were to keep experimenting, the upstream rate would converge toward zero.

So, can DSLAMs be sometimes misconfigured by Openreach techies, them maybe erroneously turning off DLM, or perhaps invoking unnecessary UPBO (upstream power backoff)? Are certain brands of DSLAM poor at performing line management?

I've discussed this upstream issue at length with both IDnet and Billion but neither have been able to offer any explanation for the sudden difference in the rate and the non-recovery of it. Downstream rate is as before, being 39.9 M bps at received power of 12.8dBm, SNRs for both directions are reasonable at 6 - 7dB. But upstream output power has halved (in logarithmic terms) from the 5.8dBm, on the 8800NL, to 2.8dBm for no plausible reason. The copper stretch to the DSLAM in the street cabinet is some 800m. The 8900AX has the latest firmware.

Any ideas about this? Upstream and downstream rates are obviously always a matter of negotiation between the DSLAM and the router, but why is DLM apparently not working and why is the 8900AX outputting such a miserably-low power level on upstream?

Edited by meditator (Sat 19-Jan-19 14:06:39)

Standard User j0hn83
(experienced) Sat 19-Jan-19 15:42:49
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Re: Can DLM sometimes fail to work at all?


[re: meditator] [link to this post]
 
DLM has nothing to do with the power levels and it doesn't adjust it dynamically.

Different modems can operate at different power levels even if they have the same chipset.

I have 2 Zyxel models with the same xdsl chipset (bcm63168) and 1 runs around 4.1dBm upstream power and the other 1.4dBm, with about 1Mb difference in upstream sync between them.

Some modems don't comply with UPBO so it could be that a neighbouring line is now using 1 of these devices.

What happens if you put the old Billion back on the line, does the power level go back up?

Nothing at all can be done about upstream power levels dropping though.

Some DSLAM firmware updates can have a considerable affect of the reported upstream power. Some of the ECI DSLAM firmware reports the upstream power incorrectly.
Standard User meditator
(fountain of knowledge) Sat 19-Jan-19 17:03:00
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Re: Can DLM sometimes fail to work at all?


[re: j0hn83] [link to this post]
 
"DLM has nothing to do with the power levels and it doesn't adjust it dynamically".

Okay, noted.

"Some modems don't comply with UPBO so it could be that a neighbouring line is now using 1 of these devices".

Well, unless that neighbouring line came into service at precisely the same moment as I completed the swapover from the 8800NL to the 8900AX, that can't be the reason.

"What happens if you put the old Billion back on the line, does the power level go back up?"

I was waiting for the obvious question. Normally, I'd have no hesitation in doing that but, in this case, the 8900AX upstream rate would take another dive, and then yet another when I put it back. I think you've forgotten that the basic problem here is that DLM is not recovering the rate. Every restart or power-down I do causes, not unexpectedly, a lowering of the upstream rate (but apparently no change in the downstream rate), which stays at each new low rate. But, who knows, in due course I might have no option but to do this.

I note what you've said about ECI DSLAMs but, on reflection, that can't be the cause in this instance because, as I've pointed out, one moment I was using the 8800NL and about 2 mins later I was using the 8900AX.

So perhaps the only conclusion possible is that dimunition in upstream rate is down to the 8900AX itself?


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Standard User j0hn83
(experienced) Sat 19-Jan-19 17:31:35
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Re: Can DLM sometimes fail to work at all?


[re: meditator] [link to this post]
 
DLM can't recover the rate if it isn't holding it back though.

DLM does not control the output power, some modems simply use a lower power and therefore can sync lower.

Swapping modems back to test would not have any adverse effect unless done multiple times in a short period.

Swapping a modem back and forth (2 resyncs) will never cause DLM to act.
Doing 10 resyncs in a row can.

If the modem reports the upstream SNRM (sometimes called noise margin) as 6dB then that's just as high as that modem will sync on the upstream.

Edited by j0hn83 (Sat 19-Jan-19 17:31:58)

Standard User meditator
(fountain of knowledge) Sat 19-Jan-19 19:06:23
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Re: Can DLM sometimes fail to work at all?


[re: j0hn83] [link to this post]
 
You make some good points.

"DLM does not control the output power, some modems simply use a lower power and therefore can sync lower".

I accept that, but you'd expect that when you use a router such as the Billion 8900AX, which costs three times that of the older Billion 8800NL, you'd at least end up with much the same ballpark rates, not where the 8900AX renders about 15% lower upstream!

Within the next 48 hrs I'll go back to using the 8800NL and see what's what. Really, I've no option but to do that at some stage, it seems to me.

One other thing that's occurred to me is that I might have a dodgy PSU. As it happens, I've a spare brick PSU of the same specification as that used with the 8900AX (I'll check with Billion first), so I'll maybe try that to see if it makes any difference.

Looking at the Billion 8900AX's stats for my FTTC connection at present, some pertinent ones are:

Downstream -
Attainable sync rate 45,146K bps
Actual sync rate 39,999K bps
SNR 7.7dB
Interleave depth 16

Upstream -
Attainable sync rate 6763K bps
Actual sync rate 6763K bps
SNR 6.2dB
Interleave depth 1

Error rates are quite good; on upstream, most of the meaningful errors are very few.

The above figures fit with what you say about 6dB dictating the max rate, albeit that there's still 0.2dB yet to go for upstream. The 8800NL did, however, sync stably at 8220K bps on upstream, at SNR 6.1dB.

Maybe, at the end of the day, the claims made by Billion that their 8900AX is their best non-commercial-grade router-modem thus far, with improved performance due to a brand new Broadcom chipset, simply don't hold true? Incidentally, I bought the 8900AX for its additional features, not in the expectation of improved rates. The rub is that I've ended up with a noticeably lower upstream rate than before. I wouldn't mind accepting a small decrease if I were syncing at significantly higher nominal rates on a more expensive broadband account, but when you lose 1.43M bps on a nominal upstream 10M bps max profile, I feel justified in being aggrieved.

BTW, do you think, when I put back the 8900AX after trying afresh with the 8800NL, it'd be worthwhile putting it back to its factory defaults and then me reconfiguring it again?
Standard User j0hn83
(experienced) Sat 19-Jan-19 19:19:02
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Re: Can DLM sometimes fail to work at all?


[re: meditator] [link to this post]
 
Broadcom chipsets tend to sync around 6.3dB.
As you can see the sync matches the attainable, the upstream has an interleaving depth of 1 which is fastpath.

This looks just like the 8900AX syncs lower on the upstream.
You may find it has a higher reported attainable on the downstream compared to the 8800NL, so would sync higher on the downstream.
Not much help with a 40Mb cap though.

The 8800NL R1 (the white version, if that's what you have) performs excellent on VDSL2 compared to some of their other models.

I know many users who use it in bridge mode, only handling the xDSL stuff, and buy a decent router to do the wireless/lan/IP.
I have this setup with my Zyxel.

I get the exact same as you with 2 different zyxel models with the same chipset.
The more expensive vmg8924-b10a syncs about 1Mb lower on the upstream than the cheaper less capable vmg1312-b10a.
I use the cheaper device that syncs higher in bridge mode with an Asus router.

My line is very similar to yours.

Max: Upstream rate = 7213 Kbps, Downstream rate = 45314 Kbps
Bearer: 0, Upstream rate = 7213 Kbps, Downstream rate = 44856 Kbps

Edited by j0hn83 (Sat 19-Jan-19 19:20:46)

Standard User meditator
(fountain of knowledge) Sat 19-Jan-19 19:52:48
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Re: Can DLM sometimes fail to work at all?


[re: j0hn83] [link to this post]
 
Yeh, Fastpath on upstream.

Is the DSL profile on VDSL2 these days still 17a? And is it worthwhile using PhyR on both upstream and downstream, as I've gathered that the latest modem-routers apply this automatically now anyway? Both routers have been configured by me for PhyR usage.

Yes, it's the original 8800NL that I still have. Jolly good little modem-router, but for me now has too few wired Ethernet ports and poor wireless range (or so they say). For various reasons, haven't wanted to introduce a separate Ethernet switch.
Standard User j0hn83
(experienced) Sat 19-Jan-19 20:03:36
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Re: Can DLM sometimes fail to work at all?


[re: meditator] [link to this post]
 
Yes it's still 17a.
PhyR isn't used.
PhyR is pretty much the same thing as G.INP(ReTx/Retransmittion).

PhyR only works on Broadcom modems to Broadcom DSLAM's, and although you are indeed on Broadcom to Broadcom kit, PhyR is never used, but G.INP instead.

It is used on newer BT Wholesale ADSL2/2+ DSLAM's in exchanges that were upgraded to 21CN in the last couple years. That's the only time I've seen it used in the UK.

You could leave it set it does no harm but it wouldn't be used.

If there is an SRA option you could enable that, as it is being trialled by OpenReach at the moment.
Standard User baby_frogmella
(knowledge is power) Sat 19-Jan-19 20:11:32
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Re: Can DLM sometimes fail to work at all?


[re: meditator] [link to this post]
 
In reply to a post by meditator:
Maybe, at the end of the day, the claims made by Billion that their 8900AX is their best non-commercial-grade router-modem thus far, with improved performance due to a brand new Broadcom chipset, simply don't hold true?


The main reason the 8900AX is expensive, isn't because it uses a broadcom DSL chipset. Its because its a Wave2 Mu-Mimo class wifi router, or in other words its a 4x4 stream router, not the cheaper 2x2 or 3x3 stream router. You've probably noticed it gives you better wifi performance than the 8800NL. Btw other 4x4 class routers also cost quite a bit, eg Asus DSL-AC88U, Netgear D7800 and TP Link VR2800.

FluidOne FTTPoD 330/30 Mbps
Linksys EA9500v2

Edited by baby_frogmella (Sat 19-Jan-19 20:12:28)

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