General Discussion
  >> Fibre Broadband


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


Pages in this thread: << 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | [20] | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | (show all)   Print Thread
Administrator MrSaffron
(staff) Sun 05-Feb-17 19:41:43
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: j0hn83] [link to this post]
 
Maybe it is that VDSL2 and ADSL2+ are doing things differently in the router.

Now just to find something that confirms this, rather than us all working from our observations.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User WWWombat
(knowledge is power) Mon 06-Feb-17 03:57:20
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: R0NSKI] [link to this post]
 
In reply to a post by R0NSKI:
I've no idea with ADSL, but that is my observations and understanding with VDSL.

I would think that wwwombat would be able to give a much more technical answer.


I didn't spend enough time on ADSL/2+ to note any inconsistent behaviour. And I don't think we have enough evidence of behaviour in VDSL2 with a target different from 6dB to be sure.

I think J0hn is correct in theory. The value 6 shouldn't be hard-coded, and should be gathered validly from the sync process. It is most certainly how I would write the code ...

But, and it is a big but, we have scant evidence that this is true for every modem, every firmware revision, every DSLAM type, every linecard type, every chipset type. Corners are cut, bugs exist, testing rushed and incomplete. People get things wrong, including the observations made by ourselves and related on here.

I've spent years watching and deciphering the DLM behaviour in FTTC, and can safely say it is always a mistake to make a definitive statement. Especially based on a sample of 1.

Best answer right now? Keep monitoring (thanks for that software, R0nski), and build a pool of evidence, looking for both the norm and the oddities. Expect to start figuring things it after a couple of months of honing those observations.
Standard User WWWombat
(knowledge is power) Mon 06-Feb-17 03:59:56
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: MrSaffron] [link to this post]
 
In reply to a post by MrSaffron:
Maybe it is that VDSL2 and ADSL2+ are doing things differently in the router.

Now just to find something that confirms this, rather than us all working from our observations.


None of the protocol specs hard-code the target.

But you can't account for how software has been written. Especially if a temporary "get things working" shortcut gets left in.


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

Standard User WWWombat
(knowledge is power) Mon 06-Feb-17 17:42:22
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: WWWombat] [link to this post]
 
In reply to a post by R0NSKI:
I would think that wwwombat would be able to give a much more technical answer.


I can see that, for VDSL2, the downstream target SNRM is sent from DSLAM (aka VTU-O) to the CPE modem (aka VTU-R) during the channel discovery phase. It is part of the signature data sent that includes tones, power and PSD.

The specification of the target SNRM indicates it is the same as in G.997.1 - which is common to many DSL specifications.

In reply to a post by WWWombat:
In reply to a post by MrSaffron:
Maybe it is that VDSL2 and ADSL2+ are doing things differently in the router.


It seems that VDSL2 modems are allowed to do different things.

The current G.993.2 specification includes 2 methods for calculating the attainable rate: a "basic" and an "improved" method. The basic one is mandatory, and the improved one is optional. And there are two variants of the improved method.

Worse, it seems that the one mandatory method, the "basic" one, wasn't fully specified in earlier versions of VDSL2, so the current specification recommends a vendor upgrades - but that recommendation is, of course, not mandatory.

The calculated attainable net data rate (ATTNDR) can be requested from the other end of the link (via messages on the EOC channel).

ATTNDR calculation:
https://s24.postimg.org/l5lzqdvyt/ITU_VDSL2_ATTNDR.png

"Basic" method:
https://s28.postimg.org/imthy6s1p/ITU_VDSL2_ATTNDR_b...
Note that it takes account of "all coding gains", which probably explains why it gets a higher value when FEC is turned on.

"Improved" method:
https://s29.postimg.org/80ygjon47/ITU_VDSL2_ATTNDR_i...

There's plenty of scope for variation within that lot, even if everything gets coded correctly.
Administrator MrSaffron
(staff) Mon 06-Feb-17 19:29:37
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: WWWombat] [link to this post]
 
Thanks for the time digging, seems to mean we will need to be careful about what different hardware (and maybe even firmware versions) is reporting

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User j0hn83
(member) Tue 07-Feb-17 01:48:24
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: WWWombat] [link to this post]
 
Argh! I was sifting through my downloaded documents looking for that page when discussing this here a few days ago!
Note how all 3 listed specifically reference TARSNRM. None reference any specific figure like 6dB.
Standard User j0hn83
(member) Tue 07-Feb-17 01:58:40
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: MrSaffron] [link to this post]
 
Absolutely yes. I only trust stats from specific vdsl2 chipset vendors anyway.
Standard User Ignitionnet
(knowledge is power) Tue 07-Feb-17 12:27:13
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year *DELETED*


[re: R0NSKI] [link to this post]
 
Post deleted by Ignitionnet
Standard User PhilipD
(experienced) Tue 07-Feb-17 12:48:05
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: adslmax] [link to this post]
 
Hi

As posted in ISPreview, the 3db profile will not be rolled out on ECI cabinets.

A question to those more knowledgeabl on such things, does a line with a reduced margin which sync's higher contribute more cross talk? Or is the frequency usage and power the same, and all that is changed are the amount of bits in each tone?

Regards

Phil
Standard User MHC
(sensei) Tue 07-Feb-17 13:01:56
Print Post

Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: PhilipD] [link to this post]
 
They may be a very, very, very small increase in the potential contribution to cross talk. The tones in use before will stay the same and at the same power levels however there could be some increase in bits per tone - that itself could change the nature of any radiated signals picked up by other lines as cross talk - could be good or bad. It will also allow some tones which are unused due to the existing noise floor to be brought into use and those could then start radiating and giving a potential for cross talk but the other lines will see an increase in cross talk noise but as they themselves may be working with a new 3dB margin what will be the effect?


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Pages in this thread: << 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | [20] | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | (show all)   Print Thread

Jump to