[AusNOG] VDSL / ADSL crosstalk

[John Edwards]

Hi David,

Standards-based VDSL2 DSLAMs can fall back to ADSL2+, they will definitely
use the lower frequencies if they're available. You may be able to apply
some kind of software filter to avoid causing midpoint injection issues
with exchange-based ADSL2+. You should probably avoid using a splitter to
run over the top of a PSTN service back to the exchange, that way you're
not touching Telstra's Copper Access Network (CAN) in any way.

Here's a CommsAlliance paper on the topic:
http://www.commsalliance.com.au/__data/assets/pdf_file/0020/46901/Managing-Interference-in-a-Vectored-VDSL2-environment-final.pdf

It may also depend on the type of wiring in your target building - most
cabling built in the last 15 years uses Cat5 or better, which should be
good for a 100Mhz signal and negligible crosstalk at VDSL2 power levels.
Crosstalk usually relates to street copper, designed for voice with a lower
twist rate.

The TransACT copper network in the ACT is mostly outdoor Cat5, since its
upgrade to VDSL2 there has been no evidence of crosstalk as an issue.

John




On 12 February 2016 at 07:17, David Hughes <david at hughes.com.au> wrote:

> Morning all,
>
> Can someone with experience with deployment of VDSL (or VDSL2) based
> services into an MDU environment (FTTB or "Wireless TTB" for example)
> comment on the impact it has on existing DSL services from exchanged based
> DSLAMS.  If memory serves me correctly, VDSL mostly uses frequencies
> significantly higher than DSL for most of its signalling and drops the
> volume in the range below 2MHz that DSL utilises with the aim of
> eliminating cross talk with the legacy services.
>
> Is that recollection correct?  From practical experience, is it enough to
> stop local VDSL kit from tromping over services being delivered from the
> exchange that are running over the same cable plant within the building?
>
> Also, I assume that if at some stage NBN replaced exchanged based ADSL
> with their own FTTB kit in the building then there would be crosstalk
> issues between to 2 competing VDSL DSLAMs?
>
>
>
> Thanks
>
> David
> ...
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