FTTH Active vs Passive

Justin Shore 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.

Good points
   Justin






More information about the NANOG mailing list