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Author Topic: ZyXEL VMG1312-B10A SNR slowly dropping  (Read 276 times)

Computerman142

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ZyXEL VMG1312-B10A SNR slowly dropping
« on: September 26, 2018, 06:50:56 AM »

Hi

I am having an issue with my ZyXEl and mostly any BCM63168 based device where the downstream SNR slowly starts dropping from when it first synced. Below on the stats is where my SNR was this morning, normally should be around 7db. I had to reboot the ZyXel as it getting to a rather low level. The only BCM63168 device I have that hasn't done this is the Huawei HG635 and stays solid around 7db on tests in the past. I'm not sure what is different between that device and these others, could it be the DSL driver version? If so does anyone know of a firmware that has this issue fixed? I don't fancy having to reboot it every 10 days. I have seen other threads with people such @skyeci having the same issue with the same ZyXEL as mine so it not just me. Never had this issue with HG612 which I know uses the older predecessor version of this chipset BCM6368. Does anyone else have or had experienced this issue? Many Thanks

VDSL Training Status:   Showtime
                    Mode:   VDSL2 Annex B
            VDSL Profile:   Profile 17a
                G.Vector:   Disable
            Traffic Type:   PTM Mode
             Link Uptime:   10 days: 14 hours: 57 minutes
====================================================================================
       VDSL Port Details       Upstream         Downstream
               Line Rate:      4.662 Mbps       20.057 Mbps
    Actual Net Data Rate:      4.643 Mbps       19.999 Mbps
          Trellis Coding:         ON                ON
              SNR Margin:        6.7 dB            1.6 dB
            Actual Delay:          8 ms             16 ms
          Transmit Power:        7.2 dBm           7.2 dBm
           Receive Power:       -4.1 dBm         -21.0 dBm
              Actual INP:        2.5 symbols       8.0 symbols
       Total Attenuation:        0.0 dB          27.8 dB
Attainable Net Data Rate:      4.684 Mbps       21.000 Mbps
====================================================================================
  VDSL Band Status        U0      U1      U2      U3      U4      D1      D2      D3
  Line Attenuation(dB):    5.3    54.6    63.3     N/A     N/A    22.5    68.1    90.3   
Signal Attenuation(dB):    5.3    54.3     N/A     N/A     N/A    31.4    67.6     N/A   
        SNR Margin(dB):    6.6    6.7     N/A     N/A     N/A    1.6    1.6     N/A   
         TX Power(dBm):    1.1    6.0     N/A     N/A     N/A    10.3    6.1     N/A   
====================================================================================

            VDSL Counters

           Downstream        Upstream
Since Link time = 57 min 35 sec
FEC:      828208901      79404
CRC:      810      38
ES:      121      26
SES:      3      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Latest 15 minutes time = 12 min 58 sec
FEC:      21002974      5
CRC:      0      0
ES:      0      0
SES:      0      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Previous 15 minutes time = 15 min 0 sec
FEC:      24605953      100
CRC:      0      0
ES:      0      0
SES:      0      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Latest 1 day time = 14 hours 57 min 58 sec
FEC:      1237058722      4007
CRC:      66      1
ES:      14      1
SES:      0      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Previous 1 day time = 24 hours 0 sec
FEC:      1327836548      6943
CRC:      67      1
ES:      23      1
SES:      0      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Total time = 1 days 14 hours 57 min 58 sec
FEC:      828208901      79404
CRC:      810      38
ES:      121      26
SES:      3      0
UAS:      23      23
LOS:      0      0
LOF:      0      0
LOM:      0      0
====================================================================================

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johnson

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Re: ZyXEL VMG1312-B10A SNR slowly dropping
« Reply #1 on: September 26, 2018, 07:57:22 AM »

I have no idea if your issue is related to DSL firmware versions, but if you want to experiment with different ones:

Current latest release uses A2pv6F039v.

Older A2pv6F039o1:
ftp://ftp2.zyxel.com/VMG1312-B10A/firmware/VMG1312-B10A_1.00(AAJZ.7)C0.zip

Newer (extracted from VMG3925) A2pv6F039x1:
https://www.dropbox.com/s/kmg26ew3nyr0puk/1312-B10A-AAJZ16-jumboframes-oldtelnet-customcmds-x1.bin?dl=0
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Weaver

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Re: ZyXEL VMG1312-B10A SNR slowly dropping
« Reply #2 on: September 26, 2018, 08:35:36 AM »

If the SNR is dropping then the interference pattern must be changing over time and the bits-per-bin or but loading allocation pattern must be getting less and less appropriate. I wonder if there is something weird happening such as bitswap being disabled at one or the other end.

How does one check the status of bitswap ?

A lack of the monitored tones feature would cause this in some situations, but that is not true for this modem as it is extremely capable.

Whatever is happening, it is not a problem as it is doing what it is designed to do. It will resync on its own if the SNRM gets way too low.

If you force a resync at certain well-chosen times of day every n days then you will get more speed out of it. But the problem I find is how on earth does one find the correct moment, which is one when interference including crosstalk is favourably low?

I would check the settings carefully but otherwise I am not sure it is something to worry about unless the error counts prove very high in practice, these can be checked. The SNRM is just a number - what matters is whether or not the modems are doing their job, and that means getting packets through uncorrupted, so the error rates are the only important figures.

Of course the current SNRM value is a vital diagnostic, but keeping it high is not an end in itself, in fact rather the opposite is the case, because if the SNRM is low then that means that you have a fast aggressive modem. If it is too high then you have very high reliability, possibly excessively slow and are definitely not enjoying the speed you could get. Apologies sincerely if all this is completely obvious to you.
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Computerman142

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Re: ZyXEL VMG1312-B10A SNR slowly dropping
« Reply #3 on: October 01, 2018, 07:03:55 PM »

Sorry for the delay in response, I thought Id give it test before coming back. @johnson I had a go with the firmware, the older one made no difference, however the newer is a bit better, it fluctuates more only by a couple 0.xdb, but I think it accurately displaying it, as supposed to the old firmware which didn't and just stuck the same. The newer firmware still drops the SNR and does not come back the next day, however it wont go below 4db so far so there is an improvement, but not ideally where I would like it. Hopefully it wont be 1db this weekend again. So I still think it could be dsl driver firmware related as this version has helped a little somewhat, hopefully Broadcom will release a better version in the future. Many thanks @Johnson for amending the firmware for us to use. It is only bothering me as I either think something is wrong, or its not reporting correctly or my line will never resync if the DLM sees the same SNR and thinks the line is struggling. Plus I like to see the correct SNR so i know what my attainable is, so know if I can resync and or if there extra speed left in my line. Plus I dont fancy the line resyncing every 10-12 days if the SNR gets too low.

@Weaver, bitswap is enabled on both upstream and downstream, I assume it will be on the eci cab im connected to. How I know when to resync the modem is when the SNR is high generally when the DLM improves my lien the SNR rises a bit I have often noticed and I am seem to get the best speed then. The ES and SES errors look like they were when I had the HG612 if not as bad, not sure the extra in built filter is helping. I am aware of the lower SNR is better, would be great to have 3db profile, but that will be forever wait with an ECI cabinet, along with G.INP and the rest.
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