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Author Topic: ZyXEL VMG1312-B10A - three modems now installed  (Read 2964 times)

Weaver

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ZyXEL VMG1312-B10A - three modems now installed
« on: May 28, 2018, 01:36:48 PM »

All modems are now up and running.

A bit of a disaster, I suddenly lost 120k of downstream on line cwcc@a.1, the first-installed ZyXEL, which had been in use for a couple of weeks. Mrs Weaver accidentally pulled the phone cable out of the wall. When it came back up that's when it decided on the lower sync rate. I rebooted the modem, and that only made things very slightly worse.

Have I merely upset BT’s DLM? If so how do I get my 120k back? Would a target SNR margin reset help? I can force one using clueless.aa.net.uk controls.

That was before the other two new ZyXELs were plugged in so I’m hoping that it’s nothing to do with the presence of those other modems. I can’t see how that would be possible anyway?

As for the other two lines:
   line cwcc@a.3 : +155k downstream sync rate, 2706 to 2861 kbps. Upstream +4 kbps, 436k to 440kbps
   line cwcc@a.4 :  +22k downstream sync rate, 2830 to 2854kbps. Upstream -66 kbps [!], 496k to 430 kbps

The loss of 13% upstream on line cwcc@a.4 is really bad news and a similar loss of ~50k happened on changing modem model on line cwcc@a.1 originally. So I have now lost 176k upstream in total or around 10%. Not good at all,  dry disappointing. An expensive price to pay for a bit more upstream.

If I get line cwcc@a.1 back to where it was before this morning’s nasty accident, then I will have gained ~ +290 kbps approximately in total downstream sync rate combined across all three modems.

Perhaps I will try the reset to see if I can get my missing 120k back?
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Weaver

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Re: ZyXEL VMG1312-B10A - three modems now installed
« Reply #1 on: May 28, 2018, 02:10:57 PM »

SNR reset didn't work, only made things slightly worse. It seems to me that I really have upset BT?
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johnson

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Re: ZyXEL VMG1312-B10A - three modems now installed
« Reply #2 on: May 28, 2018, 02:15:37 PM »

I'm not sure how DLM works on ADSL lines these days, but I cant imagine <4 resyncs causing any intervention (per line).

Isnt 120kbit kind of in the noise even for this connection? Speaking from a VDSL connection view, the alignment of the moons of jupiter could cause that.

Given you are on ADSL2, do SNRM tweaks still work? An easy way to get a boost if you are not concerned about error rates or have super low ones to start with.

Edit: sure you know but:

Code: [Select]
xdslctl configure --snr 50

To drop it by 3db.
« Last Edit: May 28, 2018, 02:23:53 PM by johnson »
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Ixel

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Re: ZyXEL VMG1312-B10A - three modems now installed
« Reply #3 on: May 28, 2018, 02:46:56 PM »

I'm not sure how DLM works on ADSL lines these days, but I cant imagine <4 resyncs causing any intervention (per line).

Isnt 120kbit kind of in the noise even for this connection? Speaking from a VDSL connection view, the alignment of the moons of jupiter could cause that.

Given you are on ADSL2, do SNRM tweaks still work? An easy way to get a boost if you are not concerned about error rates or have super low ones to start with.

Edit: sure you know but:

Code: [Select]
xdslctl configure --snr 50

To drop it by 3db.

I'd have thought it was noise too, not DLM. The SNRM tweak should work for ADSLx connections on Broadcom devices, unlike Lantiq/Infineon devices where the SNRM offset works for both ADSLx and VDSL2 connections.
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johnson

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Re: ZyXEL VMG1312-B10A - three modems now installed
« Reply #4 on: May 28, 2018, 02:57:32 PM »

I'd have thought it was noise too, not DLM. The SNRM tweak should work for ADSLx connections on Broadcom devices, unlike Lantiq/Infineon devices where the SNRM offset works for both ADSLx and VDSL2 connections.

Indeed. Also shouldn't DLM messing come later on, even with ADSL, with VDSL you will not see the results of noise bursts or numerous reconnects till the next monitoring period some time < 24 hours later.

I should add that SNRM changes will cause a resync, so if you are worried about DLM its best to leave it be or do it on one of the lines that you have reset the least today.

I used to use the SNRM tweaks all the time back with ADSL max connections, going from 12+db margins to 3... would love to have that kind of control again and would be all over it if I had 3 different lines to test.
« Last Edit: May 28, 2018, 02:59:57 PM by johnson »
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Weaver

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Re: ZyXEL VMG1312-B10A - three modems now installed
« Reply #5 on: May 28, 2018, 04:36:11 PM »

I have the downstream target SNRM set to 3dB by AA's control panel server - that is something I can just change myself, they expose these controls to customers.

As for ‘in the noise’ 120k drop is ~4%. I don't get much variation at all. It is just such a nuisance successive drops have wiped out a lot of the improvement initially seen by exchanging one DLink modem for a ZyXEL. Started out with something like 3.1Mbps downstream sync, then down to 3.055 Mbps, now down to ~2.9 Mbps.
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spring

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Re: ZyXEL VMG1312-B10A - three modems now installed
« Reply #6 on: May 28, 2018, 05:15:21 PM »

I think leave it alone for a week and let DLM do its thing, I mean it was resyncs and modem swaps right o.o ?

Edit: Eh, and lack of a dying gasp because the cable was pulled out.

Edit2: Speaking of which, can I set a permanent 9db target on my VMG1312-B10A? 40/3 constant-fixed sync rate with 300 FEC per day with an SNR of DS=25 US=20 but I wonder if it would help and if the DLM wouldn't fight back? And would it have any negative effects if the sync rate is exactly the same?
Edit3: Not that I really need it as I think if I replace the two microfilters I have with new ones it would go away but it's interesting. Could be crosstalk from other lines causing this though as it's in sudden bursts throughout a day.
« Last Edit: May 28, 2018, 05:30:03 PM by spring »
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j0hn

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Re: ZyXEL VMG1312-B10A - three modems now installed
« Reply #7 on: May 28, 2018, 07:19:59 PM »

Quote
Speaking of which, can I set a permanent 9db target on my VMG1312-B10A?

Not on VDSL2.
Broadcom chipsets only allow this on ADSL.
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johnson

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Re: ZyXEL VMG1312-B10A - three modems now installed
« Reply #8 on: May 28, 2018, 07:37:16 PM »

I have the downstream target SNRM set to 3dB by AA's control panel server - that is something I can just change myself, they expose these controls to customers.

And what does it look like in practice, under or over 3db?

Just saying you could drop it a little if you want the 120kbps back, by say 1db. I have no idea what your FEC or CRC rates are, but if they are minimal and given your remote location as far as noise sources go you could live a little closer to the edge with something like:

Code: [Select]
xdslctl configure --snr 80 or 75

If it were my line I wouldnt be able to help myself.
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spring

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Re: ZyXEL VMG1312-B10A - three modems now installed
« Reply #9 on: May 28, 2018, 08:11:27 PM »

If it were mine I'd leave it running for a month before checking on it again xD

Not on VDSL2.
Broadcom chipsets only allow this on ADSL.
Ah I forgot :P

Weaver, what DSL cable are you using? I assume you've seen this thread? https://forum.kitz.co.uk/index.php/topic,20119.msg353430.html#msg353430
Seems the shorter the length it just gets better [I've seen 0.3m and 0.5m in thread].
« Last Edit: May 28, 2018, 09:21:30 PM by spring »
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