FTTH Active vs Passive
justin at justinshore.com
Tue Dec 1 13:18:01 CST 2009
Dan White wrote:
> All valid points. Deploying a strand to each customer from the CO/Cabinet
> is a good way to future proof your plant.
> However, there are some advantages to GPON - particularly if you're
> deploying high bandwidth video services. PON ONTs share 2.4Gb/s of
> bandwidth downstream, which means you can support more than a gig of video
> on each PON, if deploying in dense mode.
That's true but I'd hope it wouldn't be needed. A single residence
wouldn't get anywhere near needing 1Gbps of video bandwidth. Even with
MPEG2 and 50 HD STBs @ 19Mbps that would still leave 50Mbps for
Internet. I don't know of anyone needing that much BW for video.
PON does present the possibility of doing and RF Overlay though which
makes traditional RF possible. That's something our CATV guy talks
about often. The RF wavelength gets spun off at the NID and outputted
as traditional RF on coax. I've heard of similar things with limited
WDM from the egress side of the active Ethernet switch to the NID but I
haven't seen any in production.
> Another big advantage is in CO equipment. A 4-PON blade in a cabinet is
> going to support on the order of 256 ONTs.
This is something that I don't think many people have dealt with before.
In our rural Active FTTH environment we're not hubbing all the fiber
out of COs. Most of it hubs back to cabinets on the side of the road
and from there gets put on an Ethernet ring which ultimately terminates
in the COs. Because of this while we may have tens of thousands of
strands out in the field we don't have anywhere near that amount in a
single cabinet or CO. A lot of people think that Active FTTH means
home-running ever strand back to a single CO and that's not generally
the case. LECs usually deploy a distributed model with aggregation out
in the field in cabinets or huts and then backhaul that back to the COs.
This also means that fewer individual fiber ports get served out of
any one location. So a cabinet might have 3-4 blades in individual
chassis or it might have a 13-slot chassis with as many slots populated
to meet the demand. It seems to work well. I see what you mean though
with the port density and space savings. I think most deployments
manage to avoid the hassle but I can see where extremely dense locations
could run into trouble.
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