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[tickmike]

Of interest
 < note BT copyright
SIN498 Issue 6.0
September
2014

Generic Ethernet Access Fibre to the Cabinet (GEA-FTTC) Service and Interface Description

I found it from
http://www.sinet.bt.com/sinet/       > Newly added documents > Accept copyright < >  SIN 498 Issue 6.0
September 2014

[kitz]

Direct link should work - as long as the document is the most recent. *

http://www.sinet.bt.com/sinet/sins/pdf/498v6p0.pdf


*tested in browser where Ive not been to SINET before in

[WWWombat]

Did anyone notice the new stuff in this version?
As discovered on TBB: TBB linky

A new product: "GEA over ADSL2+"

I'll repeat my analysis:

Having read through the test specifications for GEA over ADSL2plus (in annex B), I get a feel for how they intend the product to work.

• BT specifies that GEA over ADSL2+ is intended for long lines only, so only specify tests with range options of 2km, 2.5km and 3km.
• For comparison, the corresponding tests in Annex A (for GEA over FTTC) have range options from 100m to 2.2km.
• The default line profile in the DSLAM would appear to set maximum speeds of 12Mbps down and 1.5Mbps up.
• Looks like they want to support multicast too - so presumably aims to deploy TV this way too.
• Use of PSD masks would be needed, as I described in the earlier post.

The SIN also specifies that the modem has to support SRA and PHYR (G.INP).

[kitz]

A new product: "GEA over ADSL2+"

I could be wrong on this, but Im sure BT retail already offer this as a service. Ive seen someone post on a forum a couple of months ago about this and how they were on a long D side and because their VDSL speed was less than 'x', BTr had put them on a special product and they get charged accordingly. I cant for the life of me recall what it was called now, but I do remember looking at the product on the BTr website.  I'll try see if I can rack my brains where I saw it and or do a search later.  I wish I could remember what the product was called 

The SIN also specifies that the modem has to support SRA and PHYR (G.INP).

That has definitely been there for a while...  because I quoted some of SIN498 to TPLink a while back and it was one of the requirements I noticed when I sent them the link to an earlier version of SIN498.

----
grrr.  cant find anything on it... and still cant recall where I saw it.  I dont normally visit the BT forums, but if it was on there then I would have been looking for something else.  I do remember thinking at the time - Ive not seen that before and I quickly glanced at the product..  it was something stupid though like 'Super broadband' which is absolutely no help when it comes to searching.   I have a vague recollection at the landing page I first went to, and it listed Infinity 1, Infinity2 and this third product.   Because I was trying to look for something else... I didnt really pay much attention at the time. 

[WWWombat]

I could be wrong on this, but Im sure BT retail already offer this as a service. Ive seen someone post on a forum a couple of months ago about this and how they were on a long D side and because their VDSL speed was less than 'x', BTr had put them on a special product and they get charged accordingly.

Would that be something like "Total Broadband Option 3 with Fibre", or "Faster Option 3 with Fibre"? I recall BT Retail  introduced something like this a few years ago, when they had a strict minimum threshold for the Infinity product line of 15Mbps; at the time there were 2 options within the "standard broadband" product line (hence the "option 3" part), and there was no such thing as "Infinity 2" as 80/20 hadn't started at the time.

There were the usual screw-ups when the product was first made available (sales reps mistakenly ordering a standard ADSL-based product instead); once sorted, it looked like subscribers were treated identically to Infinity subscribers after the order. They had engineer installs, with SSFP and the standard Openreach modem.

BT retail would make the discrimination based on the estimate, so (of course) some people got considerably higher speeds than estimated - and I recall seeing some actual download speeds higher than 30Mbps. That would preclude the use of any form of ADSL2+.

Unfortunate that we were subject to locked-out modems, as that means we have little evidence of what these people actually synced with.

ISPReview has this old story:
http://www.ispreview.co.uk/story/2011/07/01/bt-launch-uk-faster-total-broadband-option-3-deal-for-sub-15mbps-fttc-lines.html

The SIN also specifies that the modem has to support SRA and PHYR (G.INP).

That has definitely been there for a while...  because I quoted some of SIN498 to TPLink a while back and it was one of the requirements I noticed when I sent them the link to an earlier version of SIN498.

True - though those requirements were a subset of the whole set for VDSL2 modems, including the vectoring ones.

The section I read (and copied those requirements from) were specifically for the "GEA over ADSL2+" modems, so didn't include anything like vectoring. I thought it was worth noting, because we don't see either SRA or PHYR as part of today's DLM for ADSL2+ (which would be BT Wholesale's DLM); it gives another suggestion that BT Openreach's DLM may be headed in a new direction.

For the sake of completeness, the test specification does include tests with FEC and interleaving turned on (a lower variant with 1 symbol of INP and 8ms delay, and a higher variant with 2 symbols of INP and 16ms of delay) - so we should expect those to continue. Conversely, all profiles mentioned had a fixed 6dB target margin - suggesting that we would not see the Openreach DLM performing stepwise increases of the SNRM to 9, 12 or 15dB even on ADSL2+.

[WWWombat]

Thinking about it, this would make for an interesting installation experience.

If the estimate for VDSL2 ends up less than, say, 15Mbps, then the installation could end up with best performance on either VDSL2 or ADSL2+ ... so the engineer ought to turn up to try out both. Which might mean using two different modems.

Of course, the idea of "best" changes over time - particularly when crosstalk is taken into account. And the switch-on of vectoring could change the ise of "best" yet again.

It could end up with a very fluid choice...

[renluop]

Has this new article from TBB any connection?
http://www.thinkbroadband.com/news/6654-asdl2-from-street-cabinets-to-solve-2-mbps-usc.html

[burakkucat]

Has this new article from TBB any connection?
http://www.thinkbroadband.com/news/6654-asdl2-from-street-cabinets-to-solve-2-mbps-usc.html

Yes. Essentially Saffy has read the forum thread and decided to create a News Item based on the information contained therein.   

[NewtronStar]

Has this new article from TBB any connection?
http://www.thinkbroadband.com/news/6654-asdl2-from-street-cabinets-to-solve-2-mbps-usc.html

Yes. Essentially Saffy has read the forum thread and decided to create a News Item based on the information contained therein.   

cheeky saffy   

[kitz]

Would that be something like "Total Broadband Option 3 with Fibre", or "Faster Option 3 with Fibre"?

Im afraid I cant recall.   It wasnt 'Total' for sure.. but could possibly have been 'Faster'.

Conversely, all profiles mentioned had a fixed 6dB target margin

Hmm, so adsl following the same as VDSL.  A lot of gamers would prefer a higher SNRm than interleaving.   BToR's current solution of not being able to turn off interleaving -nor reset the DLM.   But atm we on VDSL dont seem to have any choice in the matter, and its not something that BToR seem bothered about.

I saw a BT document once that strongly implied the reason why they dont use SNRm steps is because they can be tweaked and over-ridden using DMTtool (which they mentioned by name).   

[Dray]

There was a story about it here http://www.ispreview.co.uk/story/2011/07/01/bt-launch-uk-faster-total-broadband-option-3-deal-for-sub-15mbps-fttc-lines.html

[kitz]

Thinking about it, this would make for an interesting installation experience.

If the estimate for VDSL2 ends up less than, say, 15Mbps, then the installation could end up with best performance on either VDSL2 or ADSL2+ ... so the engineer ought to turn up to try out both. Which might mean using two different modems.

Of course, the idea of "best" changes over time - particularly when crosstalk is taken into account. And the switch-on of vectoring could change the ise of "best" yet again.

It could end up with a very fluid choice...

I was searching for something earlier for my Zyxel router, when I stumbled across this link.   Not much info there, but it would appear that Zyxel have been manufacturing VDSL line cards with ADSL2/2+ fall-back for 6yrs..  so Ive no doubt the likes of ECI and Huawei wont be that far behind.

It looks like Calix have been doing this for >3yrs

adding Packet Transfer Mode technology to the platform also helps because it allows a telco to support VDSL2 technology where the copper loop length supports it and fall back to ADSL2 where it doesn't. "Not only that, but we are actually improving the bandwidth on long-loop ADSL2 deployments by about 13 percent,

[WWWombat]

Hmm, so adsl following the same as VDSL.  A lot of gamers would prefer a higher SNRm than interleaving.   BToR's current solution of not being able to turn off interleaving -nor reset the DLM.   But atm we on VDSL dont seem to have any choice in the matter, and its not something that BToR seem bothered about.

I've seen a thread or two over on the Plusnet forums that show they've been involved in some meetings between CPs and BT with the aim of adjusting the options regarding DLM tuning for FTTC. I suspect we might see some options to allow DLM to reduce speed in preference to adding latency, and allow easier control by the CP. Eventually.

Of course, use of SRA and G.INP might reduce the need for FEC & interleaving anyway, but I don't know if the latency implications of G.INP would be welcomed by gamers.

I saw a BT document once that strongly implied the reason why they dont use SNRm steps is because they can be tweaked and over-ridden using DMTtool (which they mentioned by name).   

Ooh. Not heard that before!

The NICC document on DSM (found here) reports that TRA (tiered rate adaption, or banding) is preferable to AMA (automatic margin adjustment).

However, there's no doubt that the more modern DLM techniques all aim to share the spectrum equitably amongst users, and try to avoid unilateral power increases as a way to make an individual line perform better. I guess something like DMtool subverts that kind of altruism    vs

[WWWombat]

Yes. Essentially Saffy has read the forum thread and decided to create a News Item based on the information contained therein.   

At least he referenced the forum thread from the article 

[WWWombat]

it would appear that Zyxel have been manufacturing VDSL line cards with ADSL2/2+ fall-back for 6yrs..  so Ive no doubt the likes of ECI and Huawei wont be that far behind.

The Huawei DSLAMs certainly support ADSL2+, but the phrase "fall back" from Zyxel is interesting. I wonder if that is some form of automatic fall-back, so as to select for the best speed.