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Author Topic: Testing a ZyXEL VM8924-B10A - Total Attenuation  (Read 1124 times)

RTouris

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Testing a ZyXEL VM8924-B10A - Total Attenuation
« on: February 09, 2019, 07:50:24 PM »

So having just tested my 8924-B10A on my VDSL line i get this:

Code: [Select]
====================================================================================
    VDSL Training Status:   Showtime
                    Mode:   VDSL2 Annex B
            VDSL Profile:   Profile 17a
                G.Vector:   Disable
            Traffic Type:   PTM Mode
             Link Uptime:   0 day: 0 hour: 15 minutes
====================================================================================
       VDSL Port Details       Upstream         Downstream
               Line Rate:      3.026 Mbps       30.115 Mbps
    Actual Net Data Rate:      2.997 Mbps       29.998 Mbps
          Trellis Coding:         ON                ON
              SNR Margin:       15.9 dB            8.6 dB
            Actual Delay:          0 ms             10 ms
          Transmit Power:        6.0 dBm          14.3 dBm
           Receive Power:      -12.7 dBm          -6.1 dBm
              Actual INP:        0.0 symbols       4.0 symbols
       Total Attenuation:        0.0 dB          24.9 dB
Attainable Net Data Rate:      8.137 Mbps       37.452 Mbps
====================================================================================
  VDSL Band Status        U0      U1      U2      U3      U4      D1      D2      D3
  Line Attenuation(dB): 9.1 41.0 64.0   N/A   N/A 19.7 52.1 84.0
Signal Attenuation(dB): 9.1 40.4   N/A   N/A   N/A 19.6 51.6   N/A
        SNR Margin(dB): 15.9 15.9   N/A   N/A   N/A 8.5 8.8   N/A
         TX Power(dBm): -3.7 5.4 -128.0   N/A   N/A 13.4 7.8   N/A
====================================================================================

            VDSL Counters

           Downstream        Upstream
Since Link time = 15 min 3 sec
FEC: 13912 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 15 minutes time = 38 sec
FEC: 888 0
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: 13024 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 34 34
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 1 day time = 15 min 38 sec
FEC: 13912 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 34 34
LOS: 0 0
LOF: 0 0
LOM: 0 0
Previous 1 day time = 0 sec
FEC: 0 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Total time = 15 min 38 sec
FEC: 13912 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 34 34
LOS: 0 0
LOF: 0 0
LOM: 0 0
====================================================================================

which compared to my ISP modem/router is a good 3-4mbps up, however one thing I noticed is that the total attenuation for the upstream is not reported, while at the same time the total attenuation for the downstream is reported about 5.7dB more than the ISP modem (24.9 vs. 19.2). Truth be told the DS attenuation reported by my previous modem is close to the one reported by the Zyxel in the summarising section (Line/Signal attenuation)...

Knowing that VDSL on profile 17a operates on several bands of frequencies off a wider spectrum to attain DS and US (namely D1-3 and U0-3) I'm inclined to enquire about the figure that the Zyxel reports in the main section of the stats...Given that the ISP modem reports 19.2dBm and the Zyxel shows 24.9dBm, my question is how is that derived? Is it a weighted average of (D1*a+D2*b+D3*c)/3 for example?

Thanks!
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burakkucat

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #1 on: February 09, 2019, 08:40:22 PM »

Knowing that VDSL on profile 17a operates on several bands of frequencies off a wider spectrum to attain DS and US (namely D1-3 and U0-3) I'm inclined to enquire about the figure that the Zyxel reports in the main section of the stats...Given that the ISP modem reports 19.2dBm and the Zyxel shows 24.9dBm, my question is how is that derived? Is it a weighted average of (D1*a+D2*b+D3*c)/3 for example?

That is a good question but one to which we do not know the answer. Only an analysis of the relevant code segments will reveal how those values are determined.
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j0hn

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #2 on: February 09, 2019, 09:27:24 PM »

Should really have made a new thread.
This thread is for discussing firmware releases

which compared to my ISP modem/router is a good 3-4mbps up, however one thing I noticed is that the total attenuation for the upstream is not reported, while at the same time the total attenuation for the downstream is reported about 5.7dB more than the ISP modem (24.9 vs. 19.2). Truth be told the DS attenuation reported by my previous modem is close to the one reported by the Zyxel in the summarising section (Line/Signal attenuation)...

The 24.9dB attenuation sounds the more accurate figure for your sync speed.
I would expect a 19.2dB attenuation to sync a fair bit higher than your current 30Mb

All modems report attenuation different, using their own formula/algorithm.

Have you applied a manual cap on your line?
If not then DLM has banded (capped) your sync to 30Mb down and 3Mb up.
That's a pretty harsh cap, particularly the upstream.

You should get nearer 32Mb down and more importantly imo you should get around 8Mb upstream.

Banding is usually caused by multiple resyncs in a short time period.
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burakkucat

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #3 on: February 09, 2019, 10:12:34 PM »

Should really have made a new thread.

Now done.
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RTouris

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #4 on: February 09, 2019, 10:55:10 PM »

Thanks for splitting this into a new topic. My plan is indeed capped at 30/3.., however the attainable downstream at 37mbps indicates the max given the attenuation...prior to the ISP's modem i also tested a TP-Link TD-W9980 which also gave attenuation figures close to 19-ish dBms, as well as 33-35mbps max attainable DS.., hence my original question ;)
« Last Edit: February 09, 2019, 10:57:15 PM by RTouris »
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gt94sss2

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #5 on: February 09, 2019, 11:26:06 PM »

With a 30/3 service, I'm going to take a wild guess and say you're not in the UK :)

I think your question is why is your modem reporting a higher max downstream speed given it thinks the attenuation on the line is higher than your previous modem.

Looking at your modem stats suggests to me that your line currently has interleaving on the downstream.

This often causes modems to (falsely) increase the maximum attainable speed they report as possible..
« Last Edit: February 09, 2019, 11:28:54 PM by gt94sss2 »
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RTouris

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #6 on: February 10, 2019, 06:38:32 AM »

The question is how the modem calculates the total attenuation figure given that the d1 figure in the bands section somewhat equals to that reported by the other modems. The fact that this reports higher max attainables is clearly attributed to the chipset used in this Zyxel - we can all agree to that ;)

Well spotted on the interleaved bit, however experience shows * that with interleaving on long distance lines one can squeeze a few extra mbps of throughput, so given the distance and other stats in this case the decision was an easy one to make :)

* prior to this line maxing out at 30mbps due to the plan cap, running it on fastpath would yield considerably lower sync downstream (25 vs. 21mbps).
« Last Edit: February 10, 2019, 07:04:25 AM by RTouris »
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tubaman

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #7 on: February 10, 2019, 09:25:16 AM »

My 8924 reports 0dB Total Attenuation on the upstream side as well so I suspect it's a software bug.
 :)
Code: [Select]
====================================================================================
    VDSL Training Status:   Showtime
                    Mode:   VDSL2 Annex B
            VDSL Profile:   Profile 17a
                G.Vector:   Disable
            Traffic Type:   PTM Mode
             Link Uptime:   2 days: 2 hours: 19 minutes
====================================================================================
       VDSL Port Details       Upstream         Downstream
               Line Rate:      7.414 Mbps       45.474 Mbps
    Actual Net Data Rate:      7.389 Mbps       45.475 Mbps
          Trellis Coding:         ON                ON
              SNR Margin:        5.9 dB            3.8 dB
            Actual Delay:          0 ms              0 ms
          Transmit Power:        6.4 dBm          11.9 dBm
           Receive Power:      -15.8 dBm         -23.0 dBm
              Actual INP:        0.0 symbols      51.0 symbols
       Total Attenuation:        0.0 dB          26.3 dB
Attainable Net Data Rate:      7.389 Mbps       47.699 Mbps
====================================================================================
  VDSL Band Status        U0      U1      U2      U3      U4      D1      D2      D3
  Line Attenuation(dB): 11.3 50.0   N/A   N/A   N/A 21.1 59.5 89.4
Signal Attenuation(dB): 11.3 49.7   N/A   N/A   N/A 32.8 59.2   N/A
        SNR Margin(dB): 5.9 5.9   N/A   N/A   N/A 3.8 3.8   N/A
         TX Power(dBm): -4.6 6.0   N/A   N/A   N/A 9.7 7.9   N/A
====================================================================================
« Last Edit: February 10, 2019, 11:14:23 AM by tubaman »
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RTouris

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #8 on: February 10, 2019, 12:50:53 PM »

So there goes one, one to go...on a sidenote how do most of you manage to sync with such a low DS SNR? Is 4dB standard with the ISP that you use? There's no way to tweak ZYxel's DS SNR afaik...?
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j0hn

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #9 on: February 10, 2019, 01:43:24 PM »

We all use the same UK network.
It has a 6dB target SNRM but this can be lowered to 5dB, 4dB or 3dB.

You cannot manually change the target SNRM on Broadcom chipsets on VDSL2.

The question is how the modem calculates the total attenuation figure given that the d1 figure in the bands section somewhat equals to that reported by the other modems.

Every chipset manufacturer calculates the attenuation differently.

Quote
Is it a weighted average of (D1*a+D2*b+D3*c)/3 for example?

None of us have a clue how it's calculated is the honest answer. We've discussed it in the past.

Quote
The fact that this reports higher max attainables is clearly attributed to the chipset used in this Zyxel - we can all agree to that ;)

Your max attainable being much higher than the sync is not the chipset used in the Zyxel, but is a consequence of Interleaving+INP.
It causes the modem chipset to calculate the Max Attainable incorrectly.

Quote
Well spotted on the interleaved bit, however experience shows * that with interleaving on long distance lines one can squeeze a few extra mbps of throughput, so given the distance and other stats in this case the decision was an easy one to make

The way Interleaving/INP is applied on VDSL2 in the UK causes roughly a 10% drop in sync for us.

Can you post the results of

Code: [Select]
xdslctl info --stats
The Zyxel WebUI stats are missing lots of the framing figures.

Can you also run

Code: [Select]
xdslctl info --vendor
« Last Edit: February 10, 2019, 06:10:08 PM by j0hn »
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tubaman

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #10 on: February 10, 2019, 01:45:55 PM »

The lower DS SNR goes with G.INP on the Huawei cabinet that I'm lucky enough to connect to.
Initially G.INP kicks-in and then the SNR gets lowered over a few days. It starts at 6 dB and then lowers in 1dB steps to 3dB if the line can take it. Luckily mine can.
It's all automatic - nothing you can force I'm afraid.
G.INP and 3dB SNR adds the best part of 10Mbps to my DS speed.
 :)

Edited - j0hn beat me to it!!
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RTouris

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #11 on: February 10, 2019, 06:00:44 PM »

Thanks for your input lads; i will have to come back to this at a later stage as far as extra stats etc are concerned since i reverted back to using the IPS's equipment in order to troubleshoot some setup / VoIP issues. Hopefully it won't take long!
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kitz

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #12 on: February 12, 2019, 01:57:49 AM »

How different modems measure attenuation can get complicated because there are at least 3 different main methods used to measure attenuation. 

1) Insertion or Loop Loss -  Method usually used by the line provider (ie Openreach) of the attenuation figure at a fixed frequency such as 300kHz as it gives a good indication of the loop length for estimating capacity of line speed.  This attenuation figure should always remain fairly static regardless of the technology in use - barring any changes to physical condition of the copper line.

2) Line Attenuation. - Measured during initialisation of the line on all available tones in the band plan(s).

3) Signal Attenuation. - Can be continually measured during show time, but only monitors tones actually in use.


See What is the difference between Line Attenuation and Signal Attenuation? for more information on the last two.

We don't always know which method any particular modem is using.



----

As far as the Zyxel goes, it does pretty well at giving the breakdown of both Line and Signal Attenuation per band, but you can only get these by telnetting into the CLI rather than the WebGUI.

From my observations I would hazard a guess that what they call 'Total Attenuation' is the aggregate figure of the Line Attenuation taken during sync.   
The reason I say that is because I've never observed that figure changing during showtime.   If anyone has ever seen that figure change during showtime, then the conclusion would be it is aggregate of the Signal attenuation figures. 

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RTouris

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #13 on: March 23, 2019, 10:32:42 AM »

Can you post the results of

Code: [Select]
xdslctl info --stats
The Zyxel WebUI stats are missing lots of the framing figures.

Can you also run

Code: [Select]
xdslctl info --vendor

Back with the stats that you asked for, after a rather unfortunate "upgrade" to 5mbps upstream (which evidently cut a good 7mbps from the downstream)...?

Code: [Select]
> xdslctl info --stats
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason: 200000
Last initialization procedure status: 0
Max: Upstream rate = 6812 Kbps, Downstream rate = 30650 Kbps
Bearer: 0, Upstream rate = 4997 Kbps, Downstream rate = 29586 Kbps

Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 9.5 11.5
Attn(dB): 25.2 0.0
Pwr(dBm): 12.0 1.7

VDSL2 framing
Bearer 0
MSGc: 20 54
B: 239 31
M: 1 1
T: 64 64
R: 14 6
S: 0.2581 0.2029
L: 7872 1498
D: 155 9
I: 254 38
N: 254 38

Counters
Bearer 0
OHF: 274705 70167
OHFErr: 63 0
RS: 17565903 977415
RSCorr: 2596 0
RSUnCorr: 2307 0

Bearer 0
HEC: 1337 0
OCD: 0 0
LCD: 0 0
Total Cells: 64803828 0
Data Cells: 2072052 0
Drop Cells: 0
Bit Errors: 0 0

ES: 18 0
SES: 0 0
UAS: 81 81
AS: 1139

Bearer 0
INP: 1.00 0.00
INPRein: 0.00 0.00
delay: 10 0
PER: 4.14 16.29
OR: 50.16 29.45
AgR: 29636.67 5026.26

Bitswap: 1/1 1/1

Total time = 20 min 20 sec
FEC: 2596 0
CRC: 63 0
ES: 18 0
SES: 0 0
UAS: 81 81
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 15 minutes time = 5 min 20 sec
FEC: 531 0
CRC: 3 0
ES: 1 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: 2065 0
CRC: 60 0
ES: 17 0
SES: 0 0
UAS: 81 81
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 1 day time = 20 min 20 sec
FEC: 2596 0
CRC: 63 0
ES: 18 0
SES: 0 0
UAS: 81 81
LOS: 0 0
LOF: 0 0
LOM: 0 0
Previous 1 day time = 0 sec
FEC: 0 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Since Link time = 18 min 59 sec
FEC: 2596 0
CRC: 63 0
ES: 18 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
NTR: mipsCntAtNtr=0 ncoCntAtNtr=0

Code: [Select]
> xdslctl info --vendor
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason: 200000
Last initialization procedure status: 0
Max: Upstream rate = 6812 Kbps, Downstream rate = 30616 Kbps
Bearer: 0, Upstream rate = 4997 Kbps, Downstream rate = 29586 Kbps

ChipSet Vendor Id: BDCM:0xb1a6
ChipSet VersionNumber: 0xb1a6
ChipSet SerialNumber: AA1633FE0RL-44
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Alex Atkin UK

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Re: Testing a ZyXEL VM8924-B10A - Total Attenuation
« Reply #14 on: March 23, 2019, 10:47:47 AM »

Back with the stats that you asked for, after a rather unfortunate "upgrade" to 5mbps upstream (which evidently cut a good 7mbps from the downstream)...?

That would seem to confirm Kitz suspicion maybe?
Quote
From my observations I would hazard a guess that what they call 'Total Attenuation' is the aggregate figure of the Line Attenuation taken during sync.

As you are now using more tones then potentially the data for the calculation has changed.

In the real-world, your speed has improved.  The slight reduction in downstream speed is negligible and looking at that SNR is either intentional or just a fluke of when you last resynced and possibly would return to normal during another resync.
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