[188878] in North American Network Operators' Group
Re: DOCSIS 3.1 upstream
daemon@ATHENA.MIT.EDU (Rob Seastrom)
Wed Apr 20 13:09:40 2016
X-Original-To: Nanog@nanog.org
From: Rob Seastrom <rs-lists@seastrom.com>
In-Reply-To: <57105538.4030105@vaxination.ca>
Date: Wed, 20 Apr 2016 13:09:35 -0400
To: Jean-Francois Mezei <jfmezei_nanog@vaxination.ca>
Cc: "Nanog@nanog.org" <Nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
> On Apr 14, 2016, at 10:43 PM, Jean-Francois Mezei =
<jfmezei_nanog@vaxination.ca> wrote:
>=20
> Also, have cablecos with such limits for upstream begun to upgrade the
> cable plant to increase the upstream bandwidth ? Canadian cablecos =
have
> told the regulator it would be prohibitively expensive to do so, but
> incumbents tend to exagerate these things when it is convenient. (they
> can then claim higher costs/congestion/need for node splits which
> increates regulated wholesale rates).
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 (117 MHz is in the spec but I've =
never heard anyone talk about it). It is not uncommon to see space =
(both for the upstream and downstream) freed up by sunsetting analog =
video channels. Yes, one has to do a truck roll and swap out amplifiers =
etc. but that is relatively straightforward. The "guts" pop out of the =
enclosure that hangs from the messenger wire and are then replaced. You =
don't need to actually put a wrench on a coax connector in order to do =
this. There may need to be plant rebalancing (checking and possibly =
replacing tilt compensators) but that's something that should be =
happening on an annual basis or perhaps more often, depending on local =
practice.
Fiber nodes are similar in terms of work to swap them out, though they =
may be more modular inside.
Amplifier insides: =
https://www.arris.com/globalassets/resources/data-sheets/starline-series-b=
le100-1-ghz-line-extender-data-sheet.pdf
Fiber node insides: =
https://www.arris.com/globalassets/resources/data-sheets/sg4000-modular-4x=
4-node-data-sheet.pdf
Passives (splitters, directional taps, terminators, and the like) are =
bidirectional and typically do not need to be replaced.
Possibly useful reading for folks who want an overview of how it all =
goes together: =
http://www.cablelabs.com/wp-content/uploads/2014/12/DOCSIS3-1_Pocket_Guide=
_2014.pdf
Without having read the Canadian cable providers' representations to the =
CRTC I am ill-equipped to pass judgemenent on them, but in my personal =
opinion any discussion of "D3.1 deployment" that doesn't plan for a =
refactoring of splits is a bit dishonest.
> And would it be correct that in RFoG deployment, the 42mhz limit
> disapears as the customer equipment talks directly tothe CMTS over =
fibre
> all the way ?
RFoG is its own kettle of fish. Getting more than one channel on =
upstream for RFoG is hard. There's a scheduler for transmitting on =
individual RF channels, but not for the upstream laser, so you could =
have two lasers coming on at the same time when two cablemodems (assume =
legacy D3.0 for a moment) transmit simultaneously on 19.40 MHz and 30.60 =
MHz - in an HFC plant where the mixing happens between two different =
radio frequencies in a copper wire and then feeds an single upstream =
fiber node, one doesn't have this problem.
-r
