Messing with SNR margins. (ADSL2)

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Aaroona

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Topic # 124631 14-Jul-2013 18:10

SO I thought I would have a bit of a play with this, but before I go ahead and do so, just wanted to get some more information.

Currently, my line stats are:

Uptime:26 days, 4:10:54

DSL Type:G.992.5 annex A

Bandwidth (Up/Down) [kbps/kbps]:1.241 / 19.203

Data Transferred (Sent/Received) [kB/kB]:0,00 / 0,00

Output Power (Up/Down) [dBm]:12,5 / 0,0

Line Attenuation (Up/Down) [dB]:5,0 / 12,0

SN Margin (Up/Down) [dB]:11,5 / 8,5

If I go to mess with the SN Margin, what is the ideal figures I should be looking for?

I realize my connection itself is already quite good, but hey, I'm a geek - I play around with stuff like this for the hell of it!

RunningMan

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Reply # 855423 14-Jul-2013 18:17

The standard Chorus profile is 12dB, whereas some of the various ULL providers will go as low as 6dB.

The lower you go, the higher your sync rate is likely to be. Of course, the tradeoff is lower stability - you may see more errors showing up in the stats. If the error rate increases, then throughput will suffer as data is retransmitted.

Trial and error really!

michaelmurfy

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Reply # 855424 14-Jul-2013 18:21

Noooo! Don't do it! Makes the DSLAM angry :(

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Aaroona

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Reply # 855425 14-Jul-2013 18:22

michaelmurfy: Noooo! Don't do it! Makes the DSLAM angry :(

Explain? lol.

RunningMan: The standard Chorus profile is 12dB, whereas some of the various ULL providers will go as low as 6dB.

The lower you go, the higher your sync rate is likely to be. Of course, the tradeoff is lower stability - you may see more errors showing up in the stats. If the error rate increases, then throughput will suffer as data is retransmitted.

Trial and error really!

I thought that may be the case, so lower is usually better for sync rate.

ubergeeknz

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Reply # 855429 14-Jul-2013 18:28

Given same noise profile, a lower SNR margin will give you higher sync speed, yes

Given the speed you're syncing at you probably have a very good line. Have a look at the error statistics and see where they're at. If they are very low then you could probably go to a 6dB SNR Margin with no interleaving and get better performance.

Aaroona

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Reply # 855438 14-Jul-2013 18:54

ubergeeknz: Given same noise profile, a lower SNR margin will give you higher sync speed, yes

Given the speed you're syncing at you probably have a very good line. Have a look at the error statistics and see where they're at. If they are very low then you could probably go to a 6dB SNR Margin with no interleaving and get better performance.

Thanks for your reply;

these are the error stats I can find on the router (crap thomson)

FEC Errors (Up/Down):92 / 0

CRC Errors (Up/Down):92 / 2.207

HEC Errors (Up/Down):0 / 1.706

when combined with my uptime and data transfer, the error rates are pretty low IMO.. but I don't know a lot, so I could be wrong!

ajobbins

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Reply # 855465 14-Jul-2013 20:10

My ISP (In Australia) lets me pick from a range on their web portal

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sbiddle

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Reply # 855470 14-Jul-2013 20:19

ajobbins: My ISP (In Australia) lets me pick from a range on their web portal

That's only because you have such poor broadband over there!

There was a rumor during cabinetisation that Chorus were looking to reduce the SNR off all cabinets once complete but clearly that never happened and they made the decision to just keep the same SNR across all ISAM's for simpilification.

In reality trying to change it in your modem won't necessarily do you a lot of good.

DravidDavid

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Reply # 855572 15-Jul-2013 01:35

I whole heartedly disagree. I have a Netgear DG834G with DGTeam firmware installed. I turned my 14Mb/s line in to a 17Mb/s to 18Mb/s line when i was living in Mt Roskill. No loss of stability with interleaving off.

Even now,I live rural and my 0.9Mb/s line with a standard Dynalink is a 1.8Mb/s line with the Netgear. Same settings as in the city. It never drops either. Interleaving is still off.

Sometimes what you don't get is a blessing in disguise!

sidefx

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Reply # 855575 15-Jul-2013 01:57

DravidDavid: I turned my 14Mb/s line in to a 17Mb/s to 18Mb/s line when i was living in Mt Roskill. No loss of stability with interleaving off.

I got similar results from SNR tweaking too when on ADSL. Also with interleaving off, and zero stabilty issues. With a good old RTA1320.

Ragnor

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Reply # 856012 15-Jul-2013 17:09

The default noise margin on ADSL2+ that Chorus uses of 12dB is too conservative given cabinetisation, 6dB is the norm overseas it seems.

Geeks have been tweaking their noise margin in their modems for years, broadcom chispet modems are particularly good for this with solid results.

Chorus using 12dB still is similar to having interleaving on by default, it's the safe: "make everyone have worse performance" so they don't have to do as much troubleshooting option. /beancounters are dicks

I wonder if Chorus will activate DLM on ADSL2+, it seems to work well on VDSL2.

sidefx

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Reply # 856035 15-Jul-2013 18:10

Ragnor: I wonder if Chorus will activate DLM on ADSL2+, it seems to work well on VDSL2.

Though even on vdsl dlm chorus don't seem to use different snrm for profiles? Everything still seems to be a flat 12db target snrm.

Of course you can still tweak with dlm on vdsl - gives me some decent gains. :-)

Aaroona

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Reply # 856064 15-Jul-2013 19:10

Its a shame that my DG843 doesn't do half bridge :(

DravidDavid

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Reply # 856117 15-Jul-2013 20:29

It might with third party firmware :D

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plambrechtsen

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Reply # 856149 15-Jul-2013 21:41

Personally I wouldn't tweak it.

If your broadband is working ok enough leave it as is, if you want better broadband first ensure you have decent wiring and a master filter, and if it's still not good enough move houses.

I have rarely seen such a massive increase in speed that is noticeable for the average broadband user.

But if you want to tweak it, tweak it, if it breaks your broadband and gives you an unstable line or borks your modem. You would know why.

webwat

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Reply # 862615 20-Jul-2013 15:18

Your current noise margin of 8.5 suggests that your line has a bit of fluctuation in signal quality. Essentially it synced at 12 and that gave you enough stability to handle the fluctuations. The lower the noise margin the more throughput errors you will get until the modem eventually slows down the sync speed (with ADSL2 and above anyway) to a more stable speed. Get the master filter done before playing with SNR.

Qualified in business, certified in fibre, stuck in copper, have to keep going ^_^