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Author Topic: VDSL2 How many errors is acceptable?  (Read 972 times)

redanalog

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Re: VDSL2 How many errors is acceptable?
« Reply #15 on: May 12, 2022, 10:20:30 PM »

500 CRCs in 5 days is nothing, realtively speaking

That's 500 errored packets, a packet is between 70 bytes and 1.5Mb.
Anytime these errors are captured, the packet is resent by the source

You'll have no issues in the real world with these kinds of errors
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tubaman

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Re: VDSL2 How many errors is acceptable?
« Reply #16 on: May 13, 2022, 08:18:45 AM »

I would agree. From my experience of experimenting with Fritzbox and Zyxel, I found no difference. I therefore don't believe that matching the chipset with the Exchange is crucial (or if it is, it has minimal impact on the improvement of the quality of the connection), as modern Lantiq chipsets are as good with Broadcom-based cabinets.

On a short line with high sync the chipset probably doesn't make a significant difference. However, on longer lines I can assure you it can very much make the difference between a stable, low errors, connection and an unstable ,high errors, one.
I say this from the experience of trying many different routers and chipsets on my ~800m line. From those I have tried a BCM63168 works best on my line. The common mode filter in my Zyxel VMG8924-B10A also gives an improvement on models without one.
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j0hn

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Re: VDSL2 How many errors is acceptable?
« Reply #17 on: May 13, 2022, 04:02:25 PM »

500 CRCs in 5 days is nothing, realtively speaking

That's 500 errored packets, a packet is between 70 bytes and 1.5Mb.
Anytime these errors are captured, the packet is resent by the source

You'll have no issues in the real world with these kinds of errors

500 CRC can be 1 ES or 500 ES.

Whether any data is resent or not depends entirely on what the user is doing at the time (TCP/UDP/etc).
It could be that nothing is resent.

They are on different layers so there's not necessarily a correlation between the 2.
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Alex Atkin UK

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Re: VDSL2 How many errors is acceptable?
« Reply #18 on: May 13, 2022, 10:34:47 PM »

On a short line with high sync the chipset probably doesn't make a significant difference. However, on longer lines I can assure you it can very much make the difference between a stable, low errors, connection and an unstable ,high errors, one.
I say this from the experience of trying many different routers and chipsets on my ~800m line. From those I have tried a BCM63168 works best on my line. The common mode filter in my Zyxel VMG8924-B10A also gives an improvement on models without one.

Plus on an ECI cabinet with a really clean line, using a Lantiq modem that lets you tweak the SNRm is useful.

I only get full sync thanks to pushing a 4dB SNRm due to increased crosstalk over the years.
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j0hn

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Re: VDSL2 How many errors is acceptable?
« Reply #19 on: May 14, 2022, 01:26:24 PM »

Plus on an ECI cabinet with a really clean line, using a Lantiq modem that lets you tweak the SNRm is useful.

Same benefit for Huawei cabinets. Not all lines are deemed worthy of a sub 6dB target by the DLM.
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Alex Atkin UK

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Re: VDSL2 How many errors is acceptable?
« Reply #20 on: May 14, 2022, 09:48:59 PM »

Same benefit for Huawei cabinets. Not all lines are deemed worthy of a sub 6dB target by the DLM.

There are lines stable enough that wont just trigger DLM to increase the SNRm?
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Edinburgh_lad

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Re: VDSL2 How many errors is acceptable?
« Reply #21 on: May 15, 2022, 09:48:24 PM »

My line within 'acceptable parameters' (3 days but all these errors from 11am this morning), whatever is adding to the noise eventually made the line drop.
« Last Edit: May 16, 2022, 01:23:12 AM by Edinburgh_lad »
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Chrysalis

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Re: VDSL2 How many errors is acceptable?
« Reply #22 on: May 16, 2022, 09:42:10 AM »

Same benefit for Huawei cabinets. Not all lines are deemed worthy of a sub 6dB target by the DLM.

I have done it three times, and all three times I got banded. :)  So at least in my experience the SNRM tweaking you have to be careful as the DLM doesnt seem to like you having a SNRM way below the target.  I guess ok if its not extreme though, like 5db instead of 6db.  I had a feeling it would happen this third time but given my line because of the FEC/interleaving cant sync above 74 anyway at 6db I gave it another go.  So didnt lose anything from the banding this time.
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Alex Atkin UK

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Re: VDSL2 How many errors is acceptable?
« Reply #23 on: May 16, 2022, 12:19:17 PM »

I have done it three times, and all three times I got banded. :)  So at least in my experience the SNRM tweaking you have to be careful as the DLM doesnt seem to like you having a SNRM way below the target.  I guess ok if its not extreme though, like 5db instead of 6db.  I had a feeling it would happen this third time but given my line because of the FEC/interleaving cant sync above 74 anyway at 6db I gave it another go.  So didnt lose anything from the banding this time.

That's what I would expect as clearly DLM has a reason for not letting you have 3dB whereas on ECI its simply because there is no lower setting.
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Weaver

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Re: VDSL2 How many errors is acceptable?
« Reply #24 on: May 16, 2022, 12:31:50 PM »

One thing that I would say to any low-SNRM tweakers. Check your CRC or ES rate. If you are getting too many ES because RS or G.INP isnít coping with cancelling all the errors out, or you donít have G.INP or PhyR, then the errors will slow down your TCP connection and you may lose any speed gain you had because of TCP retransmissions, and where you are not using TCP then you will just get lost packets and mysteriously things wonít work. The loss of packets in TCP because of corruption will cause poor TCP performance because after losing packets TCP will not only have to retransmit but will in some cases slow down and then take a while to recover speed, because it assumes that the packet loss is because of congestion. I really think it isnít worth pushing it so hard that you end up with CRC errors and ES because the subtle slowdown you get in TCP is often something you canít easily see, and thereís the aforementioned problem of non-TCP protocols such as UDP just failing which is something you really donít want to have to start debugging.

I now run my ADSL2+d/s PhyR (like G.INP) connections at 3dB downstream and 6dB upstream but I can only get away with 3dB because I have PhyR L2 retransmission capability. At 3dB, I need to keep an eye on CRCs and ES counts and I decided to keep them at zero, or near enough. For the most recent 30 mins the ES count was zero both upstream and downstream.

Before you think youíre gaining speed by reducing your SNRM, actually measure real performance with a speed tester several times and take the best result and do so before and after the change.
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j0hn

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Re: VDSL2 How many errors is acceptable?
« Reply #25 on: May 16, 2022, 03:19:17 PM »

That's what I would expect as clearly DLM has a reason for not letting you have 3dB whereas on ECI its simply because there is no lower setting.

The DLM only seems to apply banding to ECI lines for high ES.
I've never seen it apply banding on a Huawei line for high ES.
G.INP means even when pushing a line to 3dB the ES only increases a little especially when compared to the hundreds you get on fastpath.
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