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Author Topic: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.  (Read 2552 times)

j0hn

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #15 on: May 16, 2020, 02:56:02 PM »

Have you tried any of your lines on ADSL2+?

I'd be interested to see if PhyR remained enabled and if there was any increase in sync.
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ejs

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #16 on: May 16, 2020, 03:31:06 PM »

Because PhyR isn't G.998.4, what's in the G.998.4 document isn't necessarily relevant.

As far as I can tell, there are no differences of any significance that make ADSL2+ itself worse than ADSL2 on long lines. The reason that some long lines perform noticeably better on ADSL2 than on ADSL2+ is that the oldest and worst type of exchange equipment (identifiable by vendor code TSTC) is rubbish at doing ADSL2+. It's actually just as bad at doing ADSL2+ on short lines as it is at doing ADSL2+ on long lines, the difference is that you can't fix only getting 16Mb when you should get 19Mb by setting your modem to ADSL2 because ADSL2 is limited to 12Mb. I think any reasoning about noise on higher frequencies somehow making ADSL2+ worse on long lines is entirely spurious.

I'm pretty sure Weaver's lines will be much the same on ADSL2+ as on ADSL2. Any differences in the amount of interleaving memory available will be irrelevant assuming it's constrained by the maximum delay permitted, not the amount of memory.
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Weaver

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #17 on: May 16, 2020, 10:55:51 PM »

Ejs is wholly unimpressed by Burakkucatís theory.

I wasnít suggesting that the differences in the G.998.4 standards might make a practical difference in performance, even less so for me, but I was just interested to note that differences do exist.

Iím interested to learn that PhyR ≠ G.998.4. I had got the wrong idea about this; I had picked up some idea that the two might be practically equal, based on something that I thought Kitz had said, but I probably misread or misremembered.

Btw my exchange as really recent hw installed at the end of 2015, for the 21CN upgrade.

@j0hn If I remember correctly, I ran on ADSL2+ briefly and there was no difference within the statistical noise; had to be careful about resyncing itself causing changes in the sync rate even when no parameters have changed. I once did a group of tests and put all the results in a spreadsheet and I couldnít make any reliable conclusion out of it, not without a large number of tests.

Iíve attached the results; zip file containing an xlsx file. The original spreadsheet is in iOS Numbers format and I hope the conversion to Excel format hasnít mangled it up too much. If anyone has any problems I can convert to csv even.
« Last Edit: May 16, 2020, 11:04:36 PM by Weaver »
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mofa2020

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #18 on: May 16, 2020, 11:03:51 PM »

It maybe none sense but would ANNEX L on ADSL2 benefit long lines more than ANNEX A?
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Weaver

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #19 on: May 16, 2020, 11:08:17 PM »

@mofa2020 - Yes, in a way; I would think the benefit would be about the same on long lines, because on my lines the low end frequencies are very good. Clearly on a short line all the bits per bin values are going to be higher so the extra contribution from the additional annex L low bins will be greater. Annex L would be a bigger part of the whole on an ultra long line, because the higher tones are so weak that their bit loading total is small compared to the additional Annex L low bins. Anyway, Annex L would be absolutely wonderful for me.
« Last Edit: May 16, 2020, 11:14:19 PM by Weaver »
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Weaver

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #20 on: May 16, 2020, 11:21:22 PM »

In that group of tests, on two occasions I did a three-way test: adsl2 vs adsl2+ vs "auto". Auto came in the middle, but the tiny sample size, only two tests, is ridiculously small. I should have tried to work out what auto was actually choosing. That would have been interesting. I believe I can see it in the stats. I didnít have any stats for the DLink modem I was using, so I should have also tested with the ZyXEL too, on which I do have access to stats.

What will a modem do on auto? Does it have a fixed preference or does it do intelligent analysis based on stats obtained?
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Weaver

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #21 on: May 16, 2020, 11:28:03 PM »

How big do we think a DTU is on your system? I have absolutely no idea. I see the maximum is 1k, but that seems a bit large to me, no? Wouldnít there be a slight benefit from having smaller DTUs - more likely to succeed, and also a disadvantage which is increased overhead and fewer slots available in the tx queue if running into the limit on total ram vs n slots times size per slot.
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Alex Atkin UK

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #22 on: May 18, 2020, 02:13:15 PM »

What will a modem do on auto? Does it have a fixed preference or does it do intelligent analysis based on stats obtained?

I always assumed Auto just means it tries them in order from best to worst until it gets sync.  I'd be very surprised if it does anything intelligent.
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aesmith

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #23 on: May 18, 2020, 03:22:05 PM »

Just out of interest I was going to compare ADSL2 vs ADSL2+ on my line, from memory performance all seemed to be the same with the only difference being the reported attenuation.  Oddly, today if I enable ADSL2+ the line will not sync.  Disable it and it returns to normal.
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Weaver

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #24 on: July 04, 2020, 01:19:56 AM »

By the way, does anyone know how modems auto-discover which protocols are available at the other end and negotiate or go through in some order or preference ? - possibly with certain things knocked out of the list of permitted alternatives.

Is there a standard for multi-protocol negotiation? I canít look in say G.992.3 say, can I ? Perhaps thereís something in the original G.992.1 which gives at least a clue.
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burakkucat

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #25 on: July 04, 2020, 01:33:01 AM »

I have always assumed that if "all" is specified in the protocol list, a modem will try the most "advanced" protocol first and if synchronisation is not achieved will then work down the list in a stepwise fashion.

I.e. VDSL2, ADSL2+, ADSL2, ADSL (or, if you prefer it, G.993.2, G.992.5, G.992.3, G.992.1).
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Weaver

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #26 on: July 04, 2020, 02:55:19 AM »

How do you ask the other end if it can handle the protocols? Do you try one and let it fail if objected to? Or is there some exchange of protocol-dentifying information so you donít have to try and then fail?

I donít even know if itís possible to speed up the process by tweaking the allowed list and paring it down.
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ejs

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #27 on: July 04, 2020, 06:37:50 AM »

Quote
Recommendation ITU-T G.994.1 provides a flexible mechanism for digital subscriber line (DSL)
transceivers to exchange capabilities and to select a common mode of operation.
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Alex Atkin UK

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Re: An ADSL2+ CIrcuit, Deliberately Restricted as ADSL2.
« Reply #28 on: July 04, 2020, 02:40:57 PM »

Just out of interest I was going to compare ADSL2 vs ADSL2+ on my line, from memory performance all seemed to be the same with the only difference being the reported attenuation.  Oddly, today if I enable ADSL2+ the line will not sync.  Disable it and it returns to normal.

If I recall correctly, I think my upstream was considerably higher on ADSL2+ vs ADSL2.  Line is somewhere between 2-3kM.
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