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Author Topic: Tweaking Broadcom based routers  (Read 45332 times)

roseway

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Tweaking Broadcom based routers
« on: June 19, 2009, 10:29:22 AM »

Warning: this note describes an experimental hack, which as far as I know is not officially documented anywhere. Try it at your own risk!

Broadcom-based routers can be tweaked to change the target noise margin set in the exchange, using the adslctl command in telnet. With Netgear routers, the DGTeam firmware makes it possible to perform the same tweak in the web interface. But in either case the tweak is limited to about - 5.5 dB in the downward direction, so if your target noise margin has been increased to 15 dB you won't be able to get it down to less than about 9.5 dB using documented methods. Note that, without the DGTeam firmware, this tweak doesn't survive a re-boot. So if you power down the router or re-boot you'll have to enter the command again.

The normal form of the adslctl noise margin tweak command is

adslctl configure --snr N

or

adsl configure --snr N

Some firmwares use adsl, some use adslctl. I will use adslctl for the rest of this note.

where N should be between 1 and 200. The default value is 100. Lower values reduce the target noise margin, and a value of 1 reduces it by about 5.5 dB. To reduce it further you would need to use negative values of N, but the command rejects negative values. This is where the hack comes in: internally, the value of N is stored as a 16-bit signed integer (supports values between -32768 and +32767) and we can trick the command into accepting negative values by using high positive values. Values between about 65400 and 65535 would be possible; this is equivalent to a range between -136 and -1.

To give a specific example. My current router is a D-Link 2740B which has been converted to a DG834N using this method. My target noise margin is 15 dB (again) as a result of an intermittent line fault, and using the DGTeam web interface I had tweaked it down to 9.5 dB. In telnet I issued this command:

adslctl configure --snr 65480

The router immediately dropped the connection and reconnected with a noise margin of 5.6 dB, and a correspondingly higher connection speed. This pretty well matched up to expectation. So we can give a rough table of noise margin change against values of N:

N          Change in target noise margin (dB)

100            0
50             -3
1               -5.5
65500      -9
65450     -12

If you go too far, the connection will become unstable, and this may have other undesirable consequences, so do this with great care, and a little at a time.


Credits

I didn't discover this hack myself. There are several references to it on the net (try searching for adslctl tweak ) and it's not clear who found it first. So, whoever it was, I duly acknowledge them.

[Edit, thanks to b4dger comment below: this hack won't work with recent Thomson/Speedtouch firmware, because the adslctl command has been disabled.]

[Edit 2, Added reference to the fact that some firmwares use the command 'adsl', not 'adslctl'. Thanks to Solstice for drawing my attention to this.]
« Last Edit: November 03, 2009, 07:44:20 AM by roseway »
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b4dger

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Re: Tweaking Broadcom based routers
« Reply #1 on: June 19, 2009, 01:55:11 PM »

Hi roseway,
Am I right in thinking that you have to also be on a 'tweakable' firmware? i.e. It's not all Broadcom based routers?

I thought that later version Speedtouch 585v6 etc. have had this command removed.

All interesting reading though  :)
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Azzaka

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Re: Tweaking Broadcom based routers
« Reply #2 on: June 19, 2009, 03:20:22 PM »

Hi roseway,
Am I right in thinking that you have to also be on a 'tweakable' firmware? i.e. It's not all Broadcom based routers?

I thought that later version Speedtouch 585v6 etc. have had this command removed.

All interesting reading though  :)

Thats the v7 of the Thomsons.
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roseway

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Re: Tweaking Broadcom based routers
« Reply #3 on: June 19, 2009, 03:29:35 PM »

I thought I'd already replied to b4dger, but it looks as though I had a senior moment and forgot to save it. Yes, I'm sure you're right, and I've edited the message to add a comment to that effect.
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Azzaka

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Re: Tweaking Broadcom based routers
« Reply #4 on: June 19, 2009, 03:51:11 PM »

i've had one of those days mate...
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kitz

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Re: Tweaking Broadcom based routers
« Reply #5 on: June 20, 2009, 03:19:27 PM »

Thank you very much eric for bringing this info to our attention.
Main site amended accordingly :)

>> i've had one of those days mate...

Yeah me too - must be something in the air  :D
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rmccardal

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Re: Tweaking Broadcom based routers
« Reply #6 on: July 28, 2009, 01:26:32 PM »

Hi there  :),

I have been using this tweek as I also had a t-snr of 15. Unfortunately the setting reverts after a reboot of my DG834.
I changed FW to the DGTeam (0850) at the weekend, but it still doesn't seem to save the command after a reboot of the router.

Any ideas how I can make the setting 'stick'?
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roseway

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Re: Tweaking Broadcom based routers
« Reply #7 on: July 28, 2009, 02:11:34 PM »

Hi and welcome

Sorry, I didn't really make this clear. If you tweak the noise margin in the DGTeam web interface the setting is saved when you click 'Apply'. But if you do it from the telnet command line it isn't saved, and I don't know of any way to save it. What I've done is to use the web interface with the slider set at minimum, which reduces the target noise margin to about 9.5 dB, and also tweak it in the command line to get it down to 6 dB. If the router is rebooted it goes back to 9.5 dB until I tweak it manually again, but not too much is lost.
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Solstice

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Re: Tweaking Broadcom based routers
« Reply #8 on: November 03, 2009, 01:31:28 AM »

hello

first off, thankyou so much for posting this! I am on Orange and they have set my Target snr to 15db which means I usually sync at between 1800 & 2500 Kbps :(

I just used this trick on my BT Voyager 2110 router (via telnet) I've never used telnet before and Im a total noob at this type of thing but now my router is connected at 3776Kbps :)

I just wanted to know..when you say the setting isn't saved after reboot, does "reboot" mean turning the router off then back on? or does it just mean if the router drops connection because of instability, the next time it connects it will connect at 15db again?

Is this true even if I use the "save" command in telnet?

Also..I used the dmt tool and I see that after connecting at 3776 Kbps my SNRM is just 3.4db which Im guessing won't be stable for very long..(I live in the countryside and we get alot of crackles/noise on the line sometimes especially during high winds/ rain etc)

I used the command "adsl configure --snr 65450" (because "adslctl configure --snr 65450" didn't work, I don't know why)
immediately followed by the "save" command

how flexible are those numbers if I want to experiment with different ones? ie.. could I input "adsl configure --snr 65473"? or do I go up in increments of 10 or 20 for example?

thanks for any advice :)
« Last Edit: November 03, 2009, 01:34:17 AM by Solstice »
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roseway

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Re: Tweaking Broadcom based routers
« Reply #9 on: November 03, 2009, 07:37:53 AM »

'Reboot' means a full restart of the router, normally by switching it off and on again. The tweak remains in place if the router simply drops the connection and reconnects. One thing I haven't checked is what happens if you order a 'warm' reboot of the router from the web interface, so I don't know if the tweak survives this.

With the router I was using (DG834GT) I couldn't find any command to save the tweak, but there are differences between firmwares on different makes of router, so it may be the case that some have a command which saves the tweak.

You can use any whole number (within the sensible range of course) - there are no specific increments.

Your comment about adsl / adslctl is valid. As I've recently come to realise, some firmwares use one version, and some use the other. I'll edit the original message to reflect this.
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Solstice

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Re: Tweaking Broadcom based routers
« Reply #10 on: November 03, 2009, 02:13:19 PM »

Ok thankyou for everything, you've been very helpfull  ;D been connected now for 13 hours at 3776 with no disconnections!
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roseway

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Re: Tweaking Broadcom based routers
« Reply #11 on: November 03, 2009, 03:00:49 PM »

You're very welcome. Here's hoping that your faster connection holds up. :thumbs:
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kenboon

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Re: Tweaking Broadcom based routers
« Reply #12 on: November 25, 2009, 05:51:03 PM »

Thanks alot for the guide :) I have finally synced at 4mb again :)

Thanks again

Ken
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Griffy

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Re: Tweaking Broadcom based routers
« Reply #13 on: December 03, 2009, 09:38:57 PM »

This doesn't work on the DG834G v3 router, as its not Broadcomm chipset, but the AR7?

If so, is there any way I can tweak my target margin with an AR7 chip? 
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roseway

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Re: Tweaking Broadcom based routers
« Reply #14 on: December 03, 2009, 10:48:14 PM »

Quote
If so, is there any way I can tweak my target margin with an AR7 chip?

I'm afraid not, sorry.
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