What happens if DLM is switched off?

AFAIK Talktalk's (and BT's) DLM is an automated feature which monitors your ADSL line and for example if you experience frequent disconnections, the DLM increases your SNR margin thereby increasing line stability and vice versa. However if you have a stable line (like in my case) is there any other advantage? If i get it switched off by talktalk, will my actual speed be closer to my sync speed? FYI i sync at more than 16.5 meg but only get 14 meg in speed tests. As per my request TalkTalk have set my profile as 'FSNR6' (fast path, snr 6db) and then i use the DMT tool to bring down the SNR even more to get more speed.
Cheers

Edited by deleted (Thu 09-Sep-10 18:09:32)

A bit of your sync will be eaten up by ADSL low level and TCP/IP overheads. I estimate that 87% of your sync speed is converted into usable data. So for a 16.5 Mbps sync I'd expect a maximum speed test of 14.3 Mbps.

These overheads have nothing to do with DLM.

In reply to a post by john2007:

A bit of your sync will be eaten up by ADSL low level and TCP/IP overheads. I estimate that 87% of your sync speed is converted into usable data. So for a 16.5 Mbps sync I'd expect a maximum speed test of 14.3 Mbps.

These overheads have nothing to do with DLM.

Thanks for clarifying. So what (if any) are the advantages of having DLM switched off?

DLM cannot be switched off i dont think. you can have profiles changed and reset but the DLM stays on

DLM affects your Sync speed only. Your actual throughput is reduced by TCP/IP overheads, as mentioned, and by congestion in the network.

If DLM were switched off you run the risk of frequent disconnections on a noisy line. But I'm unsure whether an ISP would switch it off, if it is their policy to use it.

Are you sure that TT uses DLM on LLU? It runs constantly by BT on IPStream connections provided by any non-LLU ISP and the ISP has no hand in it.

Are you on TT LLU? Oh, I see you are, so you don't have DLM.

Edited by XRaySpeX (Thu 09-Sep-10 18:58:17)

Yes - TT have a DLM system on their LLU circuits. And yes - it can be disabled for an individual line by some tech support staff if it is believed to be causing a problem.

Thanks for the replies.

So on my line (which is near perfect in terms of stability) is it worth asking talktalk to switch off DLM?

Edited by deleted (Thu 09-Sep-10 19:24:08)

nope

In reply to a post by baby_frogmella:

In reply to a post by john2007:

A bit of your sync will be eaten up by ADSL low level and TCP/IP overheads. I estimate that 87% of your sync speed is converted into usable data. So for a 16.5 Mbps sync I'd expect a maximum speed test of 14.3 Mbps.

These overheads have nothing to do with DLM.

Thanks for clarifying. So what (if any) are the advantages of having DLM switched off?

It would allow you to trade stability for speed. IOW rather than having a stable 8Mb/s you might have an unstable 12Mb/s. For most people the time lost and irritation of instability would outweigh the speed gain. On a stable line it would make next to no difference.

So basically - forget about it. Either it's doing something useful for you or else it's having no effect.

Edited by Andrue (Thu 09-Sep-10 21:19:48)

In reply to a post by Andrue:

So basically - forget about it. Either it's doing something useful for you or else it's having no effect.

Not always.

It often masks a fault, and makes things very hard to resolve even more so where you have banded profiles etc.

It either works and you don't notice it, it works and it causes your line to be slower but more stable, or it breaks everything in a bad bad way and gives end users big head pain[1]...


[1] Where you have to wait days/weeks for a upwards shift after a burst of REIN, or a hand full of LOS events (for example) or weeks/months for a reduction of target margin and unbanding of a line.