[188897] in North American Network Operators' Group
Re: DOCSIS 3.1 upstream
daemon@ATHENA.MIT.EDU (Rob Seastrom)
Thu Apr 21 13:30:23 2016
X-Original-To: Nanog@nanog.org
From: Rob Seastrom <rs-lists@seastrom.com>
In-Reply-To: <5717FEBE.1050107@vaxination.ca>
Date: Thu, 21 Apr 2016 13:30:17 -0400
To: Jean-Francois Mezei <jfmezei_nanog@vaxination.ca>
Cc: "Nanog@nanog.org" <Nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
> On Apr 20, 2016, at 6:12 PM, Jean-Francois Mezei =
<jfmezei_nanog@vaxination.ca> wrote:
>=20
> On 2016-04-20 13:09, Rob Seastrom wrote:
>=20
>> 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=20
>=20
> 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.
>=20
> Thanks for the links as well.=C3=A9
>=20
>> RFoG is its own kettle of fish. Getting more than one channel on =
upstream for RFoG is hard.=20
>=20
> 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
