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Author Topic: ReTX status with Lantiq VRX220 chipset ...  (Read 3292 times)

madhatter

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ReTX status with Lantiq VRX220 chipset ...
« on: January 19, 2019, 02:28:21 PM »

I have a Netgear DM200 modem running OpenWRT 18.06.1.
I am on the BT 40/10 FTTC package and am interested in whether I'm on
Re-Transmission High or Low. My line is very stable and speeds appear to
be at the maximum for this package. I sync at 40Mb and get a Line profile
of about 36.80Mb.
I'm assuming that is 96.8% of 38Mb (contracted max. for this package)
- which would seem to indicate ReTX high - rather than 92% of sync speed.

I understand that the Broadcom based chipsets allow for a better/easier
command interface to determine ReTX status.

However, I've being playing around with Lantiq commands and appear to
have found some which give me line status details.

The following commands show the upstream and downstream status and
seem to show ReTX is enabled on the downstream but not on the upstream.
It's my understanding that is correct for my modem type connecting to a
Broadcom based cabinet. Whilst the first commands output appears to show
ReTX status, it doesn't show if it's High or Low.

The second command output shows my interleave depth (I think).
Is this enough to determine whether I'm on ReTX High or Low ?

Thank you in advance for any help.

# dsl_cpe_pipe.sh lfsg 0
nReturn=0 nDirection=0 bTrellisEnable=1 bBitswapEnable=1 bReTxEnable=0 bVirtualNoiseSupport=0 b20BitSupport=0

# dsl_cpe_pipe.sh lfsg 1
nReturn=0 nDirection=1 bTrellisEnable=1 bBitswapEnable=1 bReTxEnable=1 bVirtualNoiseSupport=0 b20BitSupport=0

# dsl_cpe_pipe.sh g997fpsg 0 0
nReturn=0 nChannel=0 nDirection=0 nNFEC=254 nRFEC=16 nLSYMB=2694 nINTLVDEPTH=1 nINTLVBLOCK=127 nLPATH=0

# dsl_cpe_pipe.sh g997fpsg 0 1
nReturn=0 nChannel=0 nDirection=1 nNFEC=32 nRFEC=16 nLSYMB=16 nINTLVDEPTH=1 nINTLVBLOCK=32 nLPATH=0
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j0hn

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #1 on: January 19, 2019, 02:49:43 PM »

I don't think you can tell from the Lantiq stats.

It's about 96.7% off the sync speed (40Mb) for retx low and between 91-92% for retx high.

You're on retx high.
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ejs

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #2 on: January 19, 2019, 03:07:20 PM »

It's not that ReTX is on for the downstream and off for the upstream due to your type of modem. The lfcg command should show it's enabled in each direction, if not, the lfcs command can enable support for it, if that can't, then that'll be because your VDSL firmware version is old (I think 5.7.x.x.x.x and later versions have upstream ReTX support). It's on for the downstream and off for the upstream because that's how Openreach choose to do it (granted how Openreach choose to do it is partly due to modems lacking support for it years ago).

Unfortunately the lantiq commands do not properly handle more than one bearer channel, so those framing parameters including the interleaving depth for the downstream could be for the other bearer. In any case, I don't think you can determine retransmission high or low from the interleaving depth.

If g997csg 0 1 gives ActualImpulseNoiseProtectionRein, then that's the INPRein figure, 0 indicating ReTX low and 1 indicating ReTX high. The lantiq commands output INP values in units of 0.1, so ActualImpulseNoiseProtectionRein=10 would equal INPRein=1.00.
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madhatter

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #3 on: January 19, 2019, 04:10:38 PM »

Thank you both for the updates.

The output from the g997csg command is

# dsl_cpe_pipe.sh g997csg 0 1
nReturn=0 nChannel=0 nDirection=1 ActualDataRate=39950000 PreviousDataRate=39998000 ActualInterleaveDelay=16 ActualImpulseNoiseProtection=440 ActualNetDataRate=39998000 ActualImpulseNoiseProtectionRein=0 ActualImpulseNoiseProtectionNoErasure=40

so as ActualImpulseNoiseProtectionRein=0 does that mean ReTX is low ?

Am I correct in assuming ReTX Low is better, in as much as you get more of your potential
maximum line speed ?
Regarding the line itself, I live next door to my local exchange and the green cabinet (PCP)
and it's associated fibre cabinet are about 100 yards away in the opposite direction.
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j0hn

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #4 on: January 19, 2019, 05:22:37 PM »

Retx Low gives a better throughput with the IP profile being around 96.7%.
It is only an exact figure of 96.69% on Broadcom chipsets.

Retx High gives an IP profile of 91-92%

ActualImpulseNoiseProtectionRein=0  might suggest your line is retx low, but the IP profile is that of an retx high sync.
It's exactly 92%

Some ISP's will be happy to run a GEA test for you which will state the DLM profile of retx high/low, but it quotes the line from 13 days ago so recent changes would be missing.
« Last Edit: January 19, 2019, 05:25:29 PM by j0hn »
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madhatter

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #5 on: January 19, 2019, 05:38:19 PM »

Certainly appears that I'm on ReTX low but a ReTX high profile.

I wonder if it's the same situation as that reported in this recent thread.

https://forum.kitz.co.uk/index.php/topic,22971.0.html

 
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tiffy

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #6 on: January 19, 2019, 06:05:45 PM »

@madhatter:

Examples of Re-Tx high & low profiles on lines I monitor both with Broadcom chipset routers, identified as Re-Tx high & low by Bearer 0 INPRein being 1 & 0 respectifully as observed on DSLStats.

My line, 40/10 provision, Re-Tx low:
DS Synch = 40.00 Mbps.
BTW IP profile = 38.67 Mbps.
Data (synch) ratio = 38.67 / 40.00 X 100 = 96.67%

My sons line, 80/20 provision, Re-Tx high:
DS Synch = 74.92 Mbps.
BTW IP profile = 68.83 Mbps.
Data (synch) ratio = 68.83 / 74.92 X 100 = 91.87%

All exactly as J0hn has said, just some practical examples which may help understanding.

Purely from observation and going back to when MDWS was active, Bearer 0 INP value is always 50 or greater with Re-Tx high and less than 50 with Re-Tx low.
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madhatter

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #7 on: January 20, 2019, 11:48:57 AM »

Thank you @tiffy for confirming the expected profiles with both
ReTX High and Low.

Looks like I should have a higher profile but the other thread I
linked to also appears to have people with the same situation.
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j0hn

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #8 on: January 20, 2019, 12:30:12 PM »

It would need a GEA test 13 days after you took the stats to confirm.

ejs has pointed out the Lantiq stats don't differentiate between bearers, and there's 2 different INPRein values.

Bearer0, INPRein 0/1 on Broadcom modems will show retx low/high.

Bearer1, INPRein does not indicate either way.

I've confirmed the Bearer 0 INPRein is a reliable indicator of the ReTx state by comparing multiple lines and their IP profiles and having users request GEA tests to confirm.

A single result from a modem that you can't differentiate between bearers, with an incorrect IP profile and no GEA test, isn't conclusive.

So far they example of the IP profile being incorrect is on lines with full 80Mb sync.
I'm yet to see an example with a sync below the maximum, though I believe this is likely a red herring.

Who is your ISP?
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ejs

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #9 on: January 20, 2019, 02:15:35 PM »

Considering that ActualImpulseNoiseProtection=440 ActualNetDataRate=39998000 must be for Bearer 0 based on their values, it seems unlikely that ActualImpulseNoiseProtectionRein=0 would be for Bearer 1. Also, when do you ever see INPRein=0 for Bearer 1? Bearer 1 usually has its INP and INPRein figures both at the same small non-zero value.

Also, considering it's a very stable line that's presumably easily reaching the full 40/10 speeds, there's no reason why it would have been put on to retransmission high.
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j0hn

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #10 on: January 20, 2019, 06:36:12 PM »

The majority of that last post I could agree with.

Quote
Also, considering it's a very stable line that's presumably easily reaching the full 40/10 speeds, there's no reason why it would have been put on to retransmission high.

This not so much.
Retransmission High is the default and appears to be always tried first, particularly with lower SNRM targets.
DLM tends to ignore that a line is at the product limit and lowers the target SNRM anyway.

We have threads created on capping our lines to force retx low for a reason, DLM uses it much less than retx high.
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ejs

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #11 on: January 20, 2019, 07:19:39 PM »

Even if any of that is true, wouldn't the line being capped at the product rate have much the same effect as capping the line yourself, hence leading it towards retx low?

I thought retransmission low was the default, and is what gets applied when retransmission is initially enabled, and besides problematic lines, it was only the lower target SNRMs that tended to produce retransmission high, at least for Broadcom modems.
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j0hn

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #12 on: January 20, 2019, 08:27:44 PM »

Yes and that's how it should and used to work, but DLM often ignores the lower product caps and lowers the SNRM target anyway, thus defaulting to retx high.

This appears to happen more often with lines that don't have a lot of spare SNRM after hitting the product cap (attainable not much more than sync) but as with everything DLM there is no obvious/logical pattern.

No idea if that's a Broadcom only thing, this is the first line I've seen produce detailed retransmission stats from a Lantiq modem.

I'm in agreement the line appears retx low, just with an incorrect IP profile which has happened a few times with other users recently.
A GEA test would confirm it either way.
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madhatter

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Re: ReTX status with Lantiq VRX220 chipset ...
« Reply #13 on: January 21, 2019, 09:29:12 AM »

Thank you both for the further discussion points - very interesting.

Regarding my line/ISP etc.
I'm with BT on their basic fibre package (40/10).
The modem syncs at 40Mb and my SNR margin is usually about 17.5 

I live next door to the exchange and my green cabinets are 100 yards away in the
opposite direction.
I only moved to VDSL last year when the basic fibre package cost became cheaper
than ADSL2+.
By way of comparison, on ADSL2+ I used to get speeds of about 21Mb (sync was 24Mb)
with an SNR margin of 6.

Thankfully my speed requirements are modest, so the small drop (36.8Mb rather than 38Mb)
is somewhat immaterial.
I was more interested in obtaining the stats and interpreting them correctly, hoping to 
understand more along the way.

If there are any other commands I can use to extract more line information, please let me know.
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