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Australian NBN can only use VDSL2 at low speeds
Wednesday 08 July 2015 09:56:05 by Andrew Ferguson

The National Broadband Network in Australia was for a short while seen by some as something for the UK to aspire too, then once a new Government had counted the dollars needed they decided to downgrade from lots of FTTH/FTTP to a FTTC/FTTB mixture with the more rural parts getting the wireless or satellite service they would have previously got.

Now it seems the NBN is very quickly descending into a farce, the need to co-exist with ADSL2+ in the network and a frequency plan that limits VDSL2 to using the same spectrum as ADSL2+ means that until the up to 8 MHz, 17 MHz or 30 MHz bands are opened up to VDSL2 the FTTC deployments will be limited to 12 Mbps to avoid destroying exchange based ADSL2+ signals. For FTTB where the DSLAM is in the basement of an apartment building the speeds allowed are doubled to a massive 25 Mbps.

It is thought that the frequency plans to allow VDSL2 to run properly will be approved in 2016, but one wonders why deployment went ahead before approval.

The UK frequency plan for VDSL2 does use three different power masks to ensure insignificant impact on ADSL/ADSL2+ exchange based services based on distance of the cabinet from the exchange, but this is normally not noticed by users since the profile 17a VDSL2 has lots of spectrum available to itself.


Posted by ahockings about 1 year ago
To be honest, as more people further back my long phone line sign up to VDSL2, if anything my ADSL2 is getting slightly better. Nothing to do with VDSL but rather less ADSL2 lines interfering with each other I'm guessing.
Posted by WWWombat about 1 year ago
Are you sure this is about the frequencies that can be used by VDSL2?

According to a subsequent update, the confusion appears to be about the "PIR" and "CIR" rates - which look to be the guarantees made for peak-hour usage.

Essentially, it is the same confusion we see here about the 15Mbps assured rates.
Posted by Spud2003 about 1 year ago
This story doesn't seem to have set the Whirlpool NBN forum alight.
Posted by TheEulerID about 1 year ago
This all sounds rather bizarre to me. I can only think that NBN are planning to reuse the ADSL2+ frequencies. Perhaps they have very long sub-loops and the higher VDSL frequencies aren't of much use. Of course this raises a point I've made before. It seems to me that in some areas (especially where there's no LLU), much greater reach could be achieved if all lines going via selected cabinets were serviced by FTTC using a power mask which utilised the ADSL2+ frequencies.

Of course there would have to be a capped product with similar wholesale costs to the exchange-based services.
Posted by andrew (Favicon staff member) about 1 year ago
The frequencies and power used them yes.

"NBN Co will disable Downstream Power Back-off in respect of an NBN Co Node when NBN Co is satisfied that Downstream Power Back-off is no longer required in respect of that part of the NBN Co FTTB Network or NBN Co FTTN Network (as the case may be). The Co-existence Period for Ordered Products supplied by means of that NBN Co Node will cease at such time."

The PIR and CIR are the result of the power back off.

Posted by TheEulerID about 1 year ago
Incidentally, NBN produce a weekly progress report. Early progress was snail-like, but it does seem to have accelerated with about 560k properties passed in the last 12 months (against 370k and 190k in the prior two years).

Note that this is a hugely expensive project.
Posted by WWWombat about 1 year ago
IIRC, previous calculations show that the bit-loading masked out by the PSD masks accounts for around 10Mbps, for lines running at full speed.

Obviously less of that would be available to longer lines, but it would still prove to be a useful boost.
Posted by WWWombat about 1 year ago
Here's another article that talks about the position of the CA (== NICC), and their discussions about the use of spectrum from different nodes:

The CA stuff on power masks is fine (and to be expected, given their use of FTTB too), but the stuff related to the 12/1 CIR is still pure obfuscation.

The Aussies *will* be retricted, but no more than we are here.
Posted by TheEulerID about 1 year ago

Those masked out frequencies are still. the ones that have the longest reach. Longer subloops won't get the full 10mbps, but it's still the most useful part of the spectrum. I'm not recommending this as a way of extending the reach of "superfast" speeds (although it will help), but more as a way of providing functionally useful speeds on longer lines. As an example, my brother's house gets less than 1mbps from the exchange. Their cabinet is being enabled, but it's 2km distant. If ADSL2+ frequencies were available, it might well get 10mbps using FTTC.
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