Moved: DSL-N16 Packet Loss

[Betatester548]

Hi guys.

I’ve been having packet loss issues on the upstream part of my FTTC (VDSL2) line, in the UK.

I can test this by looking at the amount of retransmission on the line when running this test:

https://speed.measurementlab.net/#/

My router is a DSL-N16.

Do any of the beta firmware’s make changes to the upstream SNR margin on VDSL?

I’ve found that I can reduce packet loss to zero by reducing the total upstream speed (with a telnet command).

But if possible, I’d much rather increase the upstream SNR Margin, to increase the line’s reliability and reduce packet loss. At the moment, the upstream SNR Margin defaults to ~6dB.

Or, is the upstream SNR margin always set by the Internet Service Provider?

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[UK Sentinel]

Welcome, ASUS DSL-N16 can encourage changes in the SNR, so maybe worth increasing to say 15dB to see if that helps with stability.

Usually stability / errors is caused on the Downstream connection, what is your SNR for Downstream ?

Alas this will have the effect of lowering you synch rate (speed) so there is always a compromise.

Screen dump of your DSL stats page would be helpful

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[Betatester548]

Hi, thanks for getting back to me.

I have set my downstream SNR margin to either 8 or 7db. This seems to reduce downstream packet loss. Downstream sync is generally 35,000kbps or 40,000kbps.

Setting the downstream SNR margin to 15db  does not help to prevent upstream packet loss (nor does 30db) on my line, if the upstream sync rate is left at default (around 18,000kbps).

Upstream attenuation is 18.5db, downstream attenuation is 10.2db. I get a approx. 1-2 CRC errors on the upstream per hour, not much.

I’ve been using the latest official firmware. My  FTTC street cabinet is an ECI model.

Is there any Asus beta firmware that can force a higher upstream SNR margin?

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[UK Sentinel]

Under Administration > DSL Setting > is an option called (UPBO – Upstream Power Back Off)

This has caused so many issues for BT OpenReach over the years, what is yours set to ?

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[Betatester548]

I’ve left UPBO enabled, other settings in the DSL setting page are set to ‘stable’.

Disabling UBPO results in erratic upstream SNR margins that change every few seconds (packet loss also increases), often below 6db, so I always leave it enabled.

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[UK Sentinel]

Perfect, UPBO enabled is what is requred by BT and others and allows the DSLAM/Cab to decide what is best from an SNR perspective.

Alas with UPBO enabled, you cannot change upstrean SNR values via CMD line.

Any idea what you DSL line attenuation is ?

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[Betatester548]

Can the upstream SNR Margin be forced much higher with UPBO disabled? If so, how?

Is there a command to set this independently of the downstream SNR Margin?

Full VDSL band stats here:

There doesn’t seem to be much difference between the ‘Line’ and ‘Signal’ attenuation figures, which I’d assume is a good thing?

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[UK Sentinel]

This is where it becomes ethical (unfortunately)

BT SIN 498 (A OPENREACH Standard) R.VDSL2.7 requires that ‘The modem shall support Upstream Power Back Off (UPBO) as defined in G.993.2[3]’

If UPBO is disabled, then this can cause cross-talk on short lines which is not good for other users sharing your local exchange/DSLAM and if BT notice, you can be disconnected (in theory).

If you based outside the UK, then there is no such limitation as a lot of owners in Turkey etc. do this, but for UK, this is not allowed and UPBO needs to remain On, which intern means you cannot change SNR (upstream)

FYI – BT OPENREACH a while ago for certain ASUS DSL Modem/Routers, disabled the option on Broadcom DSLAM for G.inp as this caused them so many issues ?

If you are on the latest firmware and still are having issues, I would consider replacing your DSL-N16

 

 

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[Betatester548]

I need some advice regarding increasing the upstream noise margin, in the UK is the upstream noise margin always 6db? I’m doubtful changing the router/modem would help if upstream noise margin can’t be changed.

I’ve heard that some internet service providers can increase the upstream noise margin, on request is that true?

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[UK Sentinel]

Betatester548 wrote:

I need some advice regarding increasing the upstream noise margin, in the UK is the upstream noise margin always 6db? I’m doubtful changing the router/modem would help if upstream noise margin can’t be changed.

Alas for VDSL UK not possible for you or ISP to change, but if Openreach engineer has visited, then they can call a colleague  in India to adjust if all else fails etc.

FYI: for DSL lines that are noisy etc. Modems using Broadcom/Lantiq  based DSL chipsets are much better than the MediaTek chipset used by your DSL N16 etc.

Have you tried the ‘quiet line test’ to see if there is any noise / interference on your line which could be the reason for your high faults etc ?

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[Betatester548]

Always seem to get packet loss regardless of the modem chipset used, unfortunately.

Quiet line test doesn’t work on my line, apparently you need a BT phoneline to do this.

Maybe I’ll try some other numbers.

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[UK Sentinel]

If that fails, plug back in ISP supplied Hub and give there technical faults team a call and ask them to see if there are any faults on your line etc.

Are you using any form of QoS, as this may help reduce Errors as will capping upstream speeds etc

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[Betatester548]

I have been enabling QOS. Curiously, I find that heavily limiting the QOS settings, so that only 100-200kbps of upstream is received seems to to result in 0% packet retransmission /loss.

Could the problem I’m getting possibly be related to a QOS problem on my DSL-N16 router? Or, the firmware itself?

I tried disabling QOS entirely, but this does not fix the packet loss issue (I still get 1% or more packet loss).

Note – After resyncing my modem, I also found that the SNR Margin on both the downstream and upstream has been set to 9db, but there is still packet loss.

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[UK Sentinel]

Betatester548 wrote:

Could the problem I’m getting possibly be related to a QOS problem on my DSL-N16 router? Or, the firmware itself?

Possibly, try limiting throughput (Up-Down) to 80% of its synch rate as see if that helps ?

Trail and error I am afraid and the DSL-N16 is an old modem – so do not expect miracles and a few CRC are to be expected

FYI: Lowering the configured maximum DSL speed will allow the DSL line to have more margin and makes the line more resilient to the effects of induced noise.

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[Betatester548]

I tested my laptop with the WIFI protocol set to 802.11a, and consistently get 0% packet loss. This does not occur with the more modern 802.11ac protocol.

On my PC, generally 0.5-2% packet loss with an ethernet cable to my router/modem.

Is the 802.11a protocol correcting the errors / packet losses on my internet connection? Or, could something else going on?

I still get packet loss with other routers…

Here are my spectrum / VDSL bit loading graphs:

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