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List:       nanog
Subject:    Re: DOCSIS 3.1 upstream
From:       Rob Seastrom <rs-lists () seastrom ! com>
Date:       2016-04-21 17:30:17
Message-ID: 6DB62C97-5B03-43B6-B509-688A966260C5 () seastrom ! com
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> On Apr 20, 2016, at 6:12 PM, Jean-Francois Mezei <jfmezei_nanog@vaxination.ca> \
> wrote: 
> On 2016-04-20 13:09, Rob Seastrom wrote:
> 
> > Going to D3.1 in a meaningful way means migrating to either a mid-split at 85 MHz \
> > or a high split at 200 MHz 
> 
> Thanks. This is what I expected. But in the past, the canadian cablecos
> had argued that removing the 42mhz upstream limitation was a huge
> endeavour (they have to convicne CRTC to keep wholesale rates up, so
> create artificial scarcity by claiming that replacing all those 42mhz
> repeaters would cost a fortune, so they have to do node splits instead.

In my opinion, that fails the sniff test.  I don't have any particular budgetary \
information but I have a really hard time believing that pervasive node splits are \
cheaper than fixing the plant's US/DS splits.

By the way, just as one typically finds downstream DOCSIS channels in the 600-ish MHz \
range because that's the space that became freshly available when the plant got \
upgraded from 400 MHz to 800 MHz, one is likely to find that the 'fat' D3.1 OFDM \
upstream channels in the freshly-freed-up space that comes from doing the split \
realignment.  Remember that you need to keep the old upstreams in order to support \
all the old crufty D2.0 and D3.0 (and, sadly, probably the odd D1.1) modems out \
there.


> Arguing at CRTC is all about finding out what incumbent statements are
> just spin and which are true.
> 
> Thanks for the links as well.é
> 
> > RFoG is its own kettle of fish.  Getting more than one channel on upstream for \
> > RFoG is hard. 
> 
> But they can allocate a single very big channel, right ?  Or did you
> mean a single traditional NTSC 6mhz channel ?

They can allocate a single very big channel, but unlike QAM modulation, with OFDM you \
can have multiple stations transmitting at the same time on the same channel.  So if \
anything, the optical beat interference from having more than one laser on at once is \
likely to be worse (for some values of worse - I don't know of anyone labbing such a \
thing up and trying to characterize just how bad it gets how fast with multiple \
transmitters - it might become intolerable with 2 on and it might not).  I ran this \
past a colleague and he said "ewwwww why would anyone do D3.1 over RFoG?".  I think \
that pretty much sums it up.

My personal opinion is that two-way RFoG is a super bad idea, but one-way RFoG on a \
WDM-separated channel to support legacy QAM (with PON for your high speed data) is \
OK, with the caveat that if you want two-way settop boxes, you're gonna have to \
figure out how to have your STBs speak Ethernet or MoCA or something to get out via \
your commodity high speed data connection.  The latter is the way that FiOS does it.

-r


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