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G.DMT vs ADSL2+

frank121
Dabbler
Posts: 10
Registered: 23-09-2015

G.DMT vs ADSL2+

Hello Smiley
I have just moved to plusnet a few days ago and I am re-using my old router which was connected to talk talk. On talk talk, my router synced at around 4800Kbps at GDMT which enabled me to get around 4.2Mbps download speed.
On Plusnet the same router selects ADSL2 and syncs between 3600Kpbs and 4200Kbps which results in a slower download speed.
My question is, will this speed improve over time as the line is adjusted or is better to try and force the router to select GDMT. I am not sure if it will synch at GDMT or if plusnet need to manually change my profile? I know I have quite a long line 3.5Km or so, so I am wondering GDMT i.e normal ADSL is better suited or if I should just be patient. Smiley
My second question is about the upload speed which sits at 445Kpbs. I read elsewhere that this is probably capped and I need to ask plusnet to enable it? I will raise a support ticket for that.
Here are the results from talk talk vs plusnet. (same line and router - pre&post switch-over)
Any advice or thoughts are appreciated.
Frank

6 REPLIES
Community Veteran
Posts: 38,460
Thanks: 1,027
Fixes: 62
Registered: 15-06-2007

Re: G.DMT vs ADSL2+

The difference is due to the fact that TalkTalk was using a 3dB noise margin whereas the Plusnet/BT version is using 6dB
It may well improve to 3dB if the automatic system thinks that the line is stable enough
Community Veteran
Posts: 5,109
Thanks: 465
Fixes: 17
Registered: 10-06-2010

Re: G.DMT vs ADSL2+

All of those speeds seem a bit low for the attenuation. Perhaps your internal wiring could be improved, especially if you have more than one phone socket.
It says it has selected ADSL2+, and the higher reported attenuation confirms that. At these speeds, it would probably be better set to ADSL2 than auto choosing ADSL2+.
frank121
Dabbler
Posts: 10
Registered: 23-09-2015

Re: G.DMT vs ADSL2+

Thanks. I am using the same router and internal wiring as I was on talktalk so I was hoping that it will improve over the next week or so.
Community Veteran
Posts: 5,109
Thanks: 465
Fixes: 17
Registered: 10-06-2010

Re: G.DMT vs ADSL2+

Considering that interleaving is already on (RS Correctable Errors non-zero), and assuming it was switched on automatically, I don't think it's likely the DLM will try a 3dB target SNR margin.
Superuser
Superuser
Posts: 11,880
Thanks: 3,243
Fixes: 22
Registered: 22-08-2007

Re: G.DMT vs ADSL2+

Hi Frank,
Also note that the US is capped - that needs uncapping as well.
ejs' observation of the depressed synch speed is the first area to address.  Is there any noise on the line?  Dial 17070 option 2.  Look at the speed issues guide - see link below.
The speeds with Talk Talk were also below expectations for the attenuation.
Kevin
pvmb
Rising Star
Posts: 292
Thanks: 23
Fixes: 1
Registered: 12-02-2014

Re: G.DMT vs ADSL2+

Quote from: Oldjim
The difference is due to the fact that TalkTalk was using a 3dB noise margin whereas the Plusnet/BT version is using 6dB

That sounds likely.
Quote
It may well improve to 3dB if the automatic system thinks that the line is stable enough

Really? I wonder how likely that is. The cows may come home, if we wait long enough, but will we be at home when they do?
My line has finally got its mojo back (fingers crossed)  - but it took 9 months.