General Discussion
  >> BTwholesale DSL Implementation


Register (or login) on our website and you will not see this ad.


  Print Thread
Standard User Oldjim
(fountain of knowledge) Mon 23-Jan-12 14:14:22
Print Post

Technology difference ADSL1 and ADSL2 giving better speeds


[link to this post]
 
I have seen a number of graphs showing speed increases when going from ADSL1 to ADSL2+ but nothing specific to ADSL2.
Given that ADSL2 uses the same frequency bands as ADSL1 is there a fairly simple technical explanation why there would be a speed gain if the extra frequency bands aren't available due to line length
Standard User mr_mojo
(knowledge is power) Mon 23-Jan-12 15:12:49
Print Post

Re: Technology difference ADSL1 and ADSL2 giving better spee


[re: Oldjim] [link to this post]
 
It uses an improved modulation type -- much like DVB-T2 vs DVB-T (http://en.wikipedia.org/wiki/DVB-T2#System_differences_with_DVB-T)

DVBT2 provides ~50% improvement over DVBT in the same bandwidth; so the same principle applies here.
Standard User RobertoS
(sensei) Mon 23-Jan-12 15:50:46
Print Post

Re: Technology difference ADSL1 and ADSL2 giving better spee


[re: Oldjim] [link to this post]
 
I assume mr_mojo is right, but would add this is why we sometimes recommend people on longish lines on ADSL2+ to force it down to ADSL2.

The logic is that some router firmwares seem to calculate a higher attenuation on ADSL2+, (approximately 3dB), perhaps by taking into account the attenuation averaged over all the theoretically available frequencies on ADSL2+, but others seem somehow to leave it unchanged from the ADSL value.

Then they report back the attenuation to the DSLAM during the sync negotiation and together with the noise values end up with an agreed sync. That's my theory anyway.

Because the attenuation is higher, but the expected additional frequencies are in fact unusable, a lower sync is obtained than if the connection is forced down to ADSL2. As ADSL2 uses the ADSL frequenies as already covered, the lower attenuation is regained, and the sync speed can increase.

Where the crossover point between ADSL2 and 2+ comes varies from line to line. A very small percentage even end up best on ADSL, for some reason I haven't thought of.

My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost. Internet connection - IDNet Home Starter Fibre. Live BQM.

"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.


Register (or login) on our website and you will not see this ad.

Administrator MrSaffron
(staff) Mon 23-Jan-12 17:53:23
Print Post

Re: Technology difference ADSL1 and ADSL2 giving better spee


[re: RobertoS] [link to this post]
 
Nice theory but don't buy it

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Administrator MrSaffron
(staff) Mon 23-Jan-12 17:57:22
Print Post

Re: Technology difference ADSL1 and ADSL2 giving better spee


[re: mr_mojo] [link to this post]
 
Same frequencies, and as you said better modulation and better error handling.

The dropping from ADSL2+ to ADSL2 giving some people better stability/speed is most likely down to the variations in coding and the way ADSL2+ is shaped to fit the ANFP in the UK. This may not be fully tested by router coders, hence the prevelance of firmware updates in this area.

ADSL2 has a nominal maximum of 12 Mbps over ADSL maximum of 8Mbps. Some places list ADSL as 12Mbps, but that is really a pre-standard ADSL2 if you dig deep enough.

The problem with ADSL2+ at the cross-over seems to be that it tries to load a bin with a few bits, but the bin is so marginal, that error correction and resyncs become too frequent. Also the higher frequencies are more prone to RF interference, hence why the IPlate/ring wire become a lot more important as ADSL2+ rolled out, and uptake increased the level of crosstalk.

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User RobertoS
(sensei) Tue 24-Jan-12 00:16:56
Print Post

Re: Technology difference ADSL1 and ADSL2 giving better spee


[re: MrSaffron] [link to this post]
 
In reply to a post by MrSaffron:
Nice theory but don't buy it
smile
My theory may be wrong as to the explanation for the 3dB rise often but not always seen, and also that dropping back to the ADSL2=ADSL attenuation is irrelevant, but in practice, as you and I both know, up to about 5500kbps ADSL2 can give better speed and/or stability than ADSL2+. As you just explained in another post but not with the rule-of-thumb sync figures.

When I used to play with the settings on my line, it was absolutely obvious from the bin-loading graphs or listings that very few ADSL2+ frequencies were used, but the attenuation was 3dB up. ADSL2 gave significantly higher speed that in my mind at the time could only be attributed to the fall in attenuation more than compensating for the loss of those higher bins.

Hence the theory, which I accept could be wrong, as to what causes the effect.

My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost. Internet connection - IDNet Home Starter Fibre. Live BQM.

"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
Standard User XRaySpeX
(eat-sleep-adslguide) Tue 24-Jan-12 01:23:34
Print Post

Re: Technology difference ADSL1 and ADSL2 giving better spee


[re: MrSaffron] [link to this post]
 
What always puzzles me is how do you get an estimate of an ADSL2 speed from the various estimators like Kitz and the usual graphs?

It can't just be the ADSL2+ speed at the lower, - 3dB, attenuation because that will always be faster than the ADSL2+ speed at the higher attenuation, up to the ADSL2 ceiling of 12 Meg. Yet it must be faster then the ADSL speed at the same attenuation, otherwise there's no point to it.

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC
Administrator MrSaffron
(staff) Tue 24-Jan-12 09:31:59
Print Post

Re: Technology difference ADSL1 and ADSL2 giving better spee


[re: XRaySpeX] [link to this post]
 
You dont, there is enough error margin that you just take the data from the graphs and hand that back out.

Once you reach 50dB attenuation, the difference between ADSL and ADSL2 is minimal i.e. 0.5Meg to 1Meg usually.

Short of getting data from 1000's of lines and flipping them between the three modes no real way to verify the graphs. Which have been smooth and inflexion points probably removed over the years.

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
  Print Thread

Jump to