DOCSIS 3.1 upstream

Rob Seastrom rs-lists at
Wed Apr 20 17:09:35 UTC 2016

> On Apr 14, 2016, at 10:43 PM, Jean-Francois Mezei <jfmezei_nanog at> wrote:
> 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:
Fiber node insides:

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:

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.


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