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Author Topic: Sync speed not changed after issues with the line after re-sync?  (Read 801 times)

misiak

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Sync speed not changed after issues with the line after re-sync?
« on: December 01, 2021, 10:28:26 AM »

Hi guys, I would need your help to understand this.

I have a new VDSL line and sometimes (usually once per day) I can observe some signal issues. SNR margin fluctuates, CRC errors are generated and interned speed is decreased. But sometimes the line drops and modem resync. What I don't understand is that immediately at the resync it resync at exactly the same line speed but I can see SNR margin is increased. Why if the other parameters are not changed ? I would expect it will raise with decreased link speed but this did not happen. So my question is why in case of line issues the modem will not resync at lower speed to prevent line problems ?

Please see attached graph, connection has been very stable until 9:30 appx. then it started to fluctuate and so does the speed. Instead of 38 Mbit/s I had 10 - 15 with speedtest. I've restarted modem manually at 10:30 and it synced at the same speed only with higher SNR (this is what I don't understand). Then the connection dropped at 10:45 and resync again at the same speed.  As you can see during this time I had lot of CRC errors. My FEC errors are usually high but during this problematic time I have much higher FEC.

Can anyone bring some light to this and tell me how to prevent the router to loose the sync? Can I somehow decrease the link speed as a tradeoff for more stable connection ? I don't know why it still syncs at 41242 despites there are line issues.

Thank you!

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broadstairs

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #1 on: December 01, 2021, 10:33:02 AM »

Just some thoughts, does this always become flaky at the same time each day? Is there anything nearby which could cause noise problems? Does it settle down after a while and if so how long?

Stuart
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misiak

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #2 on: December 01, 2021, 10:58:43 AM »

Thanks for reply.

I have the line only from Sunday evening and it was resynced 2x since then and I manually restarted once. 1st time it was probably my fault as I played with cables little bit but there were not this fluctuations. After reconnect it was perfectly stable. The problems from today it's hard to tell and I have to observe for a bit longer but yesterday at this time there were no issues in the morning.

So this problem started at 9:30 today, then after resync it was fluctuating a bit but on higher SRN margin. Nevertheless, after re-sync the speed is back at +/- 40 mbit so seems it helped. However, I'm still getting lot of CRC errors so it's not perfectly stable as it was before. Also I don't understand such high amount of FEC but as I understand this should not be a problem. It was raining in the morning and cables are wet so I don't know if this can have impact on it. Also it's worth to mention that with upstream there are absolutely no issues. This is running on much higher SNR margin but there are 0 CRC, HEC, ES and ESS! So obviously it is a problem with downstream - probably because of crosstalk ? Line is busy ? But why my link speed not decrease to improve SNR margin ??? I prefer stable connection before speed. Could it be that it is still in training ?

Thanks!
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misiak

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #3 on: December 01, 2021, 11:01:36 AM »

Sorry, just realized the CRC errors chart was cut off.
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broadstairs

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #4 on: December 01, 2021, 11:07:49 AM »

You are heavily interleaved and the FECs are a by-product. More worrying are the CRCs and the SNRM instability. Also if this is a new line it will need time to settle down somewhat. I suggest you watch closely for a couple of days and see how it goes.

You don't say where you are in the world, UK or elsewhere? Also if in the UK roughly your location would be worthwhile. I think we will need a bit more information about the what and when of the issue to try to help diagnose it further. Adding some comments to your signature on the forum about your equipment and connection saves adding it each time you post.

Stuart
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misiak

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #5 on: December 01, 2021, 11:19:48 AM »

Thanks Stuart. I will for sure update my signature. I'm quite new to DSL so I'm still learning. Before I had LTE fix connection but recently it became unstable with lot of drops so I decided to switch to VDSL2. Fiber optics is not here yet :)

Parameters:

I'm located in Slovakia - EU. My provider is Slovak Telekom and my program is 50/2 with minimum guaranteed speed 30/2 - currently this is not fulfilled because line problems and I'm getting around 15 - 20 on average. I would not mind this as it is only intermittent and my modem is not re-syncing because I need a stable connections. Modem is Zyxel VMG1312-B30A configured in router mode.

Hopefully you are right it needs some time to settle but strange yesterday there were no issues. The drop was after 1 day and 4 hours. Thanks for explanation of FECs due to interleaving. Indeed it's there and I have delay 8ms but overall ping is ~20ms so this is fine for me. Had the same with LTE.

For sure I will keep an eye on it and report here the results. Thanks again for the help!

Here some DSL stats if it can help:

Code: [Select]
adsl info --stats
adsl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    1
Last initialization procedure status:   0
Max:    Upstream rate = 38821 Kbps, Downstream rate = 57852 Kbps
Bearer: 0, Upstream rate = 5312 Kbps, Downstream rate = 41242 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):        7.6             16.3
Attn(dB):        26.6            0.0
Pwr(dBm):       -4.8            -4.9

                        VDSL2 framing
                        Bearer 0
MSGc:           36              438
B:              31              103
M:              1               1
T:              64              1
R:              10              16
S:              0.0246          0.6181
L:              13632           1592
D:              1321            46
I:              42              123
N:              42              123

                        Counters
                        Bearer 0
OHF:            3017121         417941
OHFErr:         1322            0
RS:             1158414375              3428314
RSCorr:         18253009                14
RSUnCorr:       14378           0

                        Bearer 0
HEC:            2588            0
OCD:            3               0
LCD:            3               0
Total Cells:    568422965               0
Data Cells:     12358116                0
Drop Cells:     0
Bit Errors:     0               0

ES:             306             0
SES:            16              0
UAS:            69              53
AS:             7169

                        Bearer 0
INP:            3.50            1.50
INPRein:        0.00            0.00
delay:          8               7
PER:            2.37            17.21
OR:             141.44          206.28
AgR:            41383.48        5518.08

Bitswap:        2595/2596               0/0

Total time = 2 hours 16 min 20 sec
FEC:            20959254                14
CRC:            7888            0
ES:             306             0
SES:            16              0
UAS:            69              53
LOS:            1               0
LOF:            7               0
LOM:            6               0
Latest 15 minutes time = 1 min 20 sec
FEC:            193421          0
CRC:            2               0
ES:             2               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:            2098332         0
CRC:            38              0
ES:             28              0
SES:            0               0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            0               0
Latest 1 day time = 2 hours 16 min 20 sec
FEC:            20959254                14
CRC:            7888            0
ES:             306             0
SES:            16              0
UAS:            69              53
LOS:            1               0
LOF:            7               0
LOM:            6               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 = 1 hours 59 min 27 sec
FEC:            18253009                14
CRC:            1322            0
ES:             263             0
SES:            0               0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            0               0
NTR: mipsCntAtNtr=0 ncoCntAtNtr=0
 >

[Moderator edited to surround the xDSL data with [code][/code] tags.]
« Last Edit: December 07, 2021, 03:38:14 PM by burakkucat »
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meritez

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #6 on: December 01, 2021, 12:09:05 PM »

Quote
VMG1312-B30A

Have you got Supervisor access?
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misiak

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #7 on: December 01, 2021, 12:10:10 PM »

Yes, it's my router :)
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misiak

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #8 on: December 02, 2021, 08:19:53 AM »

You are heavily interleaved and the FECs are a by-product. More worrying are the CRCs and the SNRM instability. Also if this is a new line it will need time to settle down somewhat. I suggest you watch closely for a couple of days and see how it goes.

You don't say where you are in the world, UK or elsewhere? Also if in the UK roughly your location would be worthwhile. I think we will need a bit more information about the what and when of the issue to try to help diagnose it further. Adding some comments to your signature on the forum about your equipment and connection saves adding it each time you post.

Stuart

Hi Stuart, a little update.

I've reported issue to ISP and this morning modem resync at lower speed (I don't know if they've intervened or DSLAM automatically adjusted the link speed) - 36.866 Mbps. Now CRC errors stopped (not completely but heavily reduced - only like 20 per hour, before it was in thousands) and the line is much more stable. SNR went up to 9.4dB. My speed dropped by 5Mbit/s but if it's a trade-off for stability I'm OK with that. I'm paying for 30/2 guaranteed. But I have a question, I've ordered a new router Asus DSL-AX82U and I want to see how it compares with VMG1312-B30A. This route is kind of a beast and I saw there is a setting where you can increase SNR by few dbs. Do you think it can help so make link more stable on higher sync speed ? My link reports achievable speed 60 Mbit/s at 9.4 db now.

Thanks, Michal
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Alex Atkin UK

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #9 on: December 07, 2021, 11:54:23 AM »

Hi Stuart, a little update.

I've reported issue to ISP and this morning modem resync at lower speed (I don't know if they've intervened or DSLAM automatically adjusted the link speed) - 36.866 Mbps. Now CRC errors stopped (not completely but heavily reduced - only like 20 per hour, before it was in thousands) and the line is much more stable. SNR went up to 9.4dB. My speed dropped by 5Mbit/s but if it's a trade-off for stability I'm OK with that. I'm paying for 30/2 guaranteed. But I have a question, I've ordered a new router Asus DSL-AX82U and I want to see how it compares with VMG1312-B30A. This route is kind of a beast and I saw there is a setting where you can increase SNR by few dbs. Do you think it can help so make link more stable on higher sync speed ? My link reports achievable speed 60 Mbit/s at 9.4 db now.

Thanks, Michal

ASUS DSL modems are not recommended as they usually have crap DSL modems and poor firmware support compared to their plain ethernet line.

I would never ever recommend a DSL model of Asus to anyone.

The only Asus DSL modem with a half decent chipset got about 5 minutes of support from Asus.
The DSL-AC88U hasn't had any firmware updates since 2018 and is now officially discontinued.

I still receive frequent firmware updates on my 8 year old RT-AC68U.

It's completely different teams within Asus who work on the RT models than who work on the DSL models.

The RT (router only) models are excellent.
The DSL (integrated modem) models make great doorstops.

Find me someone with the DSL-AC88U who doesn't regret purchasing it.
The owners thread on ukteckhub was FILLED with bugs Asus were working on (some present since device launch) when they randomly pulled the plug on support.

It has been left with no working multicast, a horrible 5Ghz bug and intermittent crashes
There's a ridiculous number of memory leaks meaning if you are lucky to get to 2 weeks uptime without utilisation hitting 100% and crippling the device then you're doing well.

Also tweaking the SNR offset (if you are in the UK) is fighting the dynamic line management and will almost certainly end up with your line banded eventually.  Both my ECI lines did.
« Last Edit: December 07, 2021, 11:59:33 AM by Alex Atkin UK »
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snadge

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #10 on: December 07, 2021, 11:57:39 AM »

ASUS DSL modems are not recommended as they usually have crap DSL modems and poor firmware support compared to their plain ethernet line.
https://forum.kitz.co.uk/index.php/topic,25915.msg435312.html#msg435312

+1
I've read of lots of issues with certain ASUS models having poor sync rates and dropouts on xDSL, mind I'm going back a bit here...
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misiak

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #11 on: December 07, 2021, 12:33:30 PM »

Hi guys,

You are right with Asus routers but DSL-AX82U is using broadcom chipset so this should not be issue anymore. Also read some good reviews on this particular model.

I've got it already and I've noticed some strange things, maybe you could explain because I'm clueless.

So I've connected ASUS, connection was a breeze, everything worked as it should. Synced at fixed rate as old Zyxel did, I guess it's banded connection at 45mbits (confirmed ISP set this speed). SRN about 10db. First several hours no errors minimum FECS. Everything perfect. I've noticed (and it was same with Zyxel) that always after couple of hours SRN start very slowly dropping. Does not matter if day or night, no matter of interference, whatever, simply slowly it is dropping. At the beginning FEC were slowly increasing (100/s), few CRCs as well. With time progression this tempo is increasing and after 24h FEC error rate increased to 1000/s - now I have 40794150 FEC and also 6900 CRC with 2000 ES. SNR is now ~6.9db. Now if I disconnect the cable and reconnect, I'm pretty sure it would again connect at the same speed with SNR up to 10db. This is what I don't understand, I would expect that if the sync speed is the same SNR margin and error rate would be same as before disconnection. But no, everything works great. To me it looks like DLM is decreasing SNR slowly just to test the line ? I don't know but I don't have any other explanation.

Can someone explain this behavior why the line is slowly deteriorating which probably could end with modem resync ? I really don't understand that at the beginning the connection is rock stable and after 1 day I can see ton of errors. It still works pretty fine despite of these errors I just wonder what could be the problem and how to prevent. I would prefer stability of the connection.

Concerning tweaking the SNR offset - I don't think it works at all. Because if I change the offset modem always sync at the same speed and SNR as it was before. The only thing which is impacted is the Max Rate but it's probably because it is computed by router based on SNR attenuation. If I increase offset (+) it is lower and vice versa with negative offset (-) it is higher. SNR margin is the same so I don't understand this neither :)

Thanks.
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j0hn

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #12 on: December 07, 2021, 02:31:08 PM »

The newer Asus modems do indeed have Broadcom DSL chipsets. They are much better than the likes of the DSL-AC68U with the Mediatek chipsets.

Broadcom chipsets only support SNRM offset for ADSL.
It won't work on a VDSL2 service unfortunately.
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misiak

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Re: Sync speed not changed after issues with the line after re-sync?
« Reply #13 on: December 07, 2021, 03:58:47 PM »

The newer Asus modems do indeed have Broadcom DSL chipsets. They are much better than the likes of the DSL-AC68U with the Mediatek chipsets.

Broadcom chipsets only support SNRM offset for ADSL.
It won't work on a VDSL2 service unfortunately.

Ah, thanks for info. However, I saw I can lower the connection speed if I use positive offset. My SNR target is 6 and if set stability to +6db, it will lower my max rate and so does the sync speed. With negative offset my max rate increase as well buy I'm capped at 45mbit so can't go higher.

Nevertheless, the behaviors is +/- the same and it's always great when connected and the slow degrade when it is producing lot of errors and resync is made. I don't know why I have lot of these FEC errors but it does not seem normal to me. But really what's the logic behind that my link is diying, producing lot of errors, eventually resync and all if fine again like there is no issue ?
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