For telcos, going from barely twisted copper pair to FTTH presents huge
incremental improvement. FTTN is basically a stop gap medium term
solution that is more pleasing to some beancounters.
However, for a cable company, is there an advantage to deploy FTTH/GPON
to bring light originally destined to the neighbourhood node all the way
to the home and do away with coax ?
From what I have read, cablecos limit FTTH deployments to greenfields.
Do they save much by replaciung the "node" with a simple optical
splitter which no longer limits how much upstream bandwidth is
retransmitted back to head end ?
Will there be a point in the next 10 years where cable companies might
start to upgrade brownfields from coax to FTTH as some telcos have done ?
While in Canada, FTTH deployment by telcos has been accompanied with
IPTV deployments on the data path (single wavelength), I hear that
Verizon has used twin wavelengths, on for GPON data, and one for RFoG
for TV signals. Would it be fair to state that FIOS is basically
identical to FTTH deployments by cable companies ?
Do twin wavelength systems as deployed by Verizon end up costing far
more ? Or is the price difference mininal ?
I believe the difference is fairly negligible between RFoG and IPTV. RFoG allows the cable companies to leverage the existing RF head end while FTTH requires a IPTV head end. IPTV is less familiar to most cable operators and requires new investment in facilities and skills.
Doing RFoG forward path is simple. The reverse path isn't. VZ has an
IP reverse path for VOD asset purchases and keeping their STBs in
contact with whatever element management they use.
VZ STBs depend on the the local VZ provided CPE as the reverse path for
communication.
It's been a while since I've looked at a PON deployment but I believe
the xPON waves are passively muxed with an EDFA amplified video wave and
then sent to the outside plant.
I think all of the MSOs in the US have long term (15-20 year) plans to
also do FTTH. Advances in DOCSIS and coax technology seem to be outpacing
those available on the telco twisted-pair side, so it delays forklifting
the existing HFC plant. DOCSIS 3.1 requires some significant capital
investment to do things like expand upstream channel spectrum, etc. but
the costs still pale in comparison to trenching fiber to houses and will
give them enough bandwidth to supply a lot more users with higher speed
service. There is also an evoluation to all-IP, everyone sees the writing
on the wall and many of the presentations at Cable-TEC (SCTE) in Atlanta
next week are focused on IP/IPTV, etc. Like someone else said, it's hard
to replace millions of set-top boxes that don't speak IPTV... In a lot of
ways IPTV, etc. over a big IP pipe is much simpler than what we have today
even with RFoG. But RFoG is compatible with all of the existing systems
in place.
The are interesting ways to overlay PON on top of existing HFC deployments
that aren't really all that expensive, but houses aren't really being
built these days like they used to so the opportunities to build into new
developments isn't happening like it was 5-6 years ago.
As for Verizon, I think their choice to do the 1550 video wavelength had a
lot to do with how they were ingesting video in the beginning and the
back-end systems, customer premise equipment, etc. It also doesn't
require doing things like QoS to separate Internet from video traffic.
That's no different than what MSOs are deploying as well. Using things
like DSG the STB is using IP these days to communicate with application
servers, VoD, etc. Really the same as your VZW example, the STB uses
DOCSIS for OOB signalling instead of straight RF.
PON can use a RF video overlay or not, the PON standards have stayed away
from using 1550-1560nm for that reason, but yes it's all passively muxed.
For cable companies who have the data service as part of the RFoG
wavelengths to provide coax at the CPE, how do they handle
collisions/timing on the upstream side ?
Does the ONT provide TDMA slots for the upstream wavelength to ensure
only one customer transmits RF at a time on the upstream ? Or is it all
handled within the DOCSIS /RFoG side ?