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<div class="moz-cite-prefix">On 12/02/2016 7:47 AM, David Hughes
wrote:<br>
</div>
<blockquote
cite="mid:7FD34192-3DA0-496B-89FD-69B5B0064DE6@hughes.com.au"
type="cite">
<pre wrap="">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.</pre>
</blockquote>
VDSL2 *can* have a lower or even no transmission power in the ADSL2+
band, if the provider programs the DSLAM that way, but by default it
uses the same frequencies at much the same power. The main problem
with co-existance with exchange-based gear is the mis-match of
transmission powers caused by the difference in distances from the
DSLAM to the modem. The signal from the basement VDSL DSLAM, being
so much closer to the modem than the exchange DSLAM, tends to swamp
the exchange signal which is attenuated by the time it reaches the
building. Also the other way - the VDSL modem implements "upstream
power-backoff" so it doesn't swamp the input of the very close VDSL
DSLAM, meaning the upstream signal becomes swamped by the adjacent
ADSL2+ modem which is transmitting at full power to reach the
exchange.<br>
<br>
In short, the upstream VDSL2 signal is degraded by the ADSL2+, and
the downstream ADSL2+ is degraded by the VDSL2.<br>
<br>
<br>
<blockquote
cite="mid:7FD34192-3DA0-496B-89FD-69B5B0064DE6@hughes.com.au"
type="cite">
<pre wrap="">
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?</pre>
</blockquote>
It can help in the downstream direction, but you'd need to also do
it in the upstream direction, and mask out the frequency band used
by the exchange ADSL2+ - which will reduce the VDSL2 performance
both ways. Only good pair separation can fix this. Typically each
floor in an MDU is served by a separate cable from the MDF, so you
shouldn't get any impact between VDSL2 and ADSL2+ services on
different floors - but within services on the same floor, there may
be impact.<br>
<br>
<blockquote
cite="mid:7FD34192-3DA0-496B-89FD-69B5B0064DE6@hughes.com.au"
type="cite">
<pre wrap="">
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? </pre>
</blockquote>
Yes. Its a real problem that is happening today. Comms Alliance is
working on a co-existance Code to regulate VDSL2 in-building to
promote co-existance, but today the in-building cabling is
out-of-scope for the current regulations, so an in-building VDSL2
deployment can degrade exchange-based services without much of a
regulatory come-back.<br>
<br>
This needed the Telco Act changed - see <b><span lang="EN-AU">Telecommunications
Amendment (Next-Generation Broadband Interference
Management) Regulation 2015 </span></b><span lang="EN-AU">(<a class="moz-txt-link-freetext" href="https://www.comlaw.gov.au/Details/F2015L01721">https://www.comlaw.gov.au/Details/F2015L01721</a>).<br>
<br>
The action currently is in Comms Alliance WC58 -
<a class="moz-txt-link-freetext" href="http://www.commsalliance.com.au/Activities/committees-and-groups/wc58">http://www.commsalliance.com.au/Activities/committees-and-groups/wc58</a><br>
</span><br>
Paul.<br>
<br>
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<p class="MsoNormal"><b><span
style="color:black;font-size:14.0pt;line-height:115%">Paul
Brooks</span></b></p>
<p class="MsoNormal"><b><style='color:black'>Executive GM -
Networks & Technology</style='color:black'></b></p>
<p class="MsoNormal">Email: <a class="moz-txt-link-abbreviated" href="mailto:paul.brooks@tridentsc.com.au">paul.brooks@tridentsc.com.au</a></p>
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