DOCSIS 3.1 upstream

Thu Apr 21 17:30:17 UTC 2016

> On Apr 20, 2016, at 6:12 PM, Jean-Francois Mezei <jfmezei_nanog at 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