Re: What's Difference: Fiber to Home; Curb and Hybrid Fiber/Coax

[Mark A. Cnota <mac () rci chi il us>]

Liron Lightwood (r.lightwood () trl oz au) wrote:

> I've been reading about the future networks the cable TV companies and
> telcos want to set up for video on demand, interactive TV, etc.  I'm
> getting a little confused about the various terms used for the various
> kinds of networks.

> Could someone please tell me the difference between:

> Fiber to the home,
> Fiber to the curb.
> Hybrid fiber/coax network.

I can expound on the telco applications of fiber. I would imagine for
cable tv it isn't too much different.

Fiber to the home is pretty much what it sounds like. It only gets
confusing when you compare and contrast it to "fiber to the curb."

Leaving the central office, the fiber will terminate first at a
"remote terminal" in either an underground vault or large above-ground
cabinet.  These eletronics will multiplex the optical signal down to
several of a more useable level. This is a more efficient use of
bandwith as well as making the far-end muxes cheaper because they have
a "slower" signal to deal with.  In the past these types of cabinets
and vaults used SLC-96 technology to give us derived copper
facilities, but instead now we have fiber coming OUT also.

The fiber coming out of these multiplexers can be used either of two
ways.  One is to terminals in pedstals or on poles, which would feed
two to six houses each. This is what is called "fiber to the curb."
Depending on what type of service you are providing, you either coax
or copper drop wire will go from the terminal to the subscribers
house. The other option is for the fiber to be passively split and go
directly into each subscribers house. The latter, of course, offers
much more capability for broadband services such as video on demand,
interactive information services, etc. even though this can be done
over short pieces of coax to a limited extent also.

This also brings up another real interesting point with a lot of
varying opinions. As just about everyone knows, copper telephone
service has always been line powered. That is, you have never had to
supply your own power in order for a regular telephone to work. Even
when the power goes out, you ALWAYS have telephone service, because
the central office has deisel backup and batteries to back up the
deisel. Another interesting point is they also have deisel generators
on semi-truck trailers in case the deisel generator at the central
office fails, because the batteries aren't meant to last for a real
long time. The "remote terminals" used for derived copper service have
always had battery backups, and they aren't THAT widely used so there
haven't been a lot of problems with lost power.

Here comes fiber to the curb/home. All fiber electronics need an
external power source. In fiber to the curb, Ameritech's solution is
to bury telco-type 22 ga. cable in the same trench and make the
optical terminals powered from the commercial power source at the
remote terminal. If you want to go one step further and bring fiber to
the home, the only feasible way is for the subscriber to supply the
power for the multiplexing unit. Now if you lose commercial power, you
have no telephone service. You can make a battery backup but that gets
expensive really fast, not to mention having to test and maintain it.

What is happening is a lot of people are knocking "fiber to the
curb/home" because it gives up a certain reliability factor that has
always been associated with telephone service. Are people willing to
give up the reliability of POTS for new technology? What other
solutions have been discussed by other AOC's or vendors?


Mark A. Cnota / Outside Plant Engineering, Ameritech