DLM, SNR margin adjusts etc.

Been lurking here for some time, just registered as I have some questions about SNR margins and Plusnet's DLM on ADSL.

I previously was with BE up til March and got fairly good speeds with them - up to about 19Mbit down and 2.1Mbit up with SNR of 3-6dB.

Having been on Plusnet for over a month now with the line being stable at 16.5Mbit down on a 6dB profile, I asked Plusnet if they could adjust this to 3dB but was told this was not possible... but I'm pretty sure I've read somewhere of people getting 3dB profiles on Plusnet. Apparently this had something to do with the DLM moving them after a period of stability.

Does anyone know anything about this?

From what ive read on here the BT DLM on 21cn connections can ajust to as low as 3db, also fastpath can be appied manually (so overriding DLM) the isp should be able to do this (Both)for you , I Think it's probably a case of getting to speak with the right person

Edited by tommy45 (Thu 09-May-13 18:29:00)

Unfortunately it's true.

The DLM is BT Wholesale's, and ISPs have no direct control over it. The default is 6dB, and given a period of high stability it drops automatically to 3dB. I don't know how stable it has to be, sorry.

You can get routers where you can adjust it yourself. Common ones you should be able to pick up cheaply are the Netgear 834GT (any version) and the 834Gv4. You have to be careful when "tweaking" in that way on BT Wholesale DLM, as too many reconnections in a short period can screw you up for weeks. Three of four in a hour is as much as I'd try.

More information on Netgear tweaking. I advise the DMT dropdown menus (where once you create a setting it remembers it in the menu) or CLI methods. The DGTeam method does allow the setting to be retained through a router power-cycle, but I didn't like it.

I'm fairly sure that isp's do have a fair bit of control over a 21cn connection i formed this opinion from what i 've been told by several indipendant isp's Things like fast path to be enabled permantly, dlm can be switched off too , only going by what i've been told , but it would not suprise me if it was the truth, because it's about time BT gave the isp control
As for tweaking the SNR (ds only) doesnt DLM set/cap the max attainable rate to the target snr it has set? if so reducing the margin wont vield a higher sync rate

oh, and here's some thing that backs up my opinion Rev K's blog (AAISP) So if those options are available to AAISP then those same options will be available to all the other ISP's too, It's possible that a lot of the support staff are not aware that they can make changes to the line config

Edited by tommy45 (Thu 09-May-13 19:41:06)

No the BTw DLM auto decides the Target NM and Interleaving. The most the ISP can do is set a floor for the Target NM, thereby capping the sync.

In reference to revk.www.me.uk/2011/10/bt-listening-to-us.html:

So BT have finally listened to us and soon (December I think) we will have the controls to actually make changes to the settings and turn off the DLM on lines. We aim to expose the settings on the control pages so that customers can also make changes

And he runs an ISP So should know what they can and cannot do

And as they can disable DLM then they would be able to make other changes also on a line with it switched off , I already was aware about them being able to disable dlm having been told this by more than 1 isp,

Edited by tommy45 (Fri 10-May-13 06:38:53)

In June 2012, BT Wholesale gave all ISP's the ability to login to BTW.com website and manually override ADSL2+ broadband profile connections.

The ISP rep/operator has 6 options to set, rateband, interleaving, SNR for both upstream and downstream. All changes take effect immediately with no waiting period like the previous 72Hrs or starting 10 Day training periods.

ADSL MAX is still the same, ISP's can only press reset to start a 10 day training period.


Unfortuneately, around 90% of Plusnet staff dont know this.

I'd suspect way less than 10% of Plusnet staff have the login/password for the BT Wholesale system to be able to access to things like that.