Date: Wed, 14 Oct 1992 17:40:46 GMT
From: deej@cbnewsf.cb.att.com (david.g.lewis)
Newsgroups: comp.dcom.telecom
Subject: Re: Fiber to the Home
Organization: AT&T
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 12, Issue 780, Message 2 of 6

In article <telecom12.772.9@eecs.nwu.edu>, Leonard.Erickson@f51.
n105.z1.fidonet.org (Leonard Erickson) writes:

> In TELECOM Digest V12#763 deej@cbnewsf.cb.att.com (david.g.lewis)
> writes:

>> Using your 5000 phone lines per (I'm guessing you mean) fiber pair, at
>> 64kb/s for a phone line, you're talking sending 160Mb/s to each house.
>> Let's use 155Mb/s, since that's an STS-3 SONET/SDH rate.  Anyone know
>> what an STS-3 FOT is going for these days?  I don't have any
>> up-to-date information (and if I did, I probably wouldn't be allowed
>> to post it), but I'd guess that $30k/link (both ends) is correct
>> within an order of magnitude.  Even if using ring architectures and
>> ADMs can drop your costs by a factor of two (unlikely to impossible),
>> you're talking $15k electronics costs per house.

>> Even if the cost of overlaying the fiber itself goes to zero, you've
>> just incurred a $15k per subscriber incremental cost.  At a 50,000
>> line CO, that's an investment of $750 million dollars.  For capacity
>> which will, basically, sit there until people figure out how to use
>> it.

> On the other hand, how *cheap* could a 64kb/s interface be? That's all
> it'd take to supply a "regular" phone line. And in the quantities
> involved, I'd expect the cost to drop *fast*. For the sake of
> argument, call it $50. (I've seen RS-232 to fiber adapters in that
> range).

That's a different question than the one I was answering.  I was
responding to a statement to the effect that "capacity is free, so the
telco should overbuild by a factor of 5000 because someday someone
will find a use for it."  My point was that capacity is most
emphatically *not* free; even though the cost *for fiber* is no
different whether one or 5000 equivalent phone lines is run over that
fiber, the cost of the fiber is by no means the only cost factor --
and may not even be the dominant cost factor -- in determining the
cost of providing large amounts of capacity to a user.

We could probably discuss for hours (and people do, regularly) the
economics of fiber to the home/fiber to the curb/fiber in the loop.
I'll just make some observations:

* Most RS-232 to fiber converters use multimode fibers and LED
transmitters, which are considerably less expensive than semiconductor
lasers for use with single-mode fiber.  And if you're building to
allow megabandwidth in the future, you'll build single-mode fiber.

* Depending on whose studies you believe, fiber in the subscriber loop
as far as a pedestal serving four to eight residence customers, with
copper drops from there to the demark, is somewhere between 25% above
(and dropping) to 25% below total copper distribution, on an installed
first cost (IFC) basis.  This architecture has the advantage of
pushing fiber into the loop to a certain point, with the possibility
of running it the rest of the way to the residence when the economics
improve.

* Also depending on whose studies you believe, fiber to the home is
anywhere from three to ten years away from matching copper on an
installed first cost basis.

* Regardless of whose studies you believe, all these IFC comparisons
omit from consideration cost and other factors both for and against
fiber, like cost of operations support system upgrading (against),
improved operational capabilities of fiber (for), improved quality and
reliability (for), ease of upgrading (for), and the fact that the
copper distribution plant is already there (big against).

* Telcos will generally act on whoever's studies *they* believe.
Ameritech has placed a large order for fiber in the loop equipment,
which leads me to believe that they believe that it's cheaper than
copper in some scenarios.  In general, you can expect that telcos are
somewhat intelligent when it comes to building networks, and if
something's cheaper than what they're doing now, it won't take them
*too* long to latch onto it.

> And if you need extra capacity, instead of running more lines, you
> replace the interface box at the user premises.

Indeed, this is one large advantage of fiber.

> I'm not sure whether the CO end of the fiber would be better served
> by a box capable of handling a range of line capcities, or by a
> dedicated box.

A "box" capable of handling a range of capacities without changing any
hardware is, currently, a myth.  Some systems (like AT&T's DDM-2000)
use one system framework (processor, low-speed interfaces, common
elements, etc.)  with several different varieties of optical interface
for different line speeds (e.g. OC-3 and OC-12), but if you change the
line speed, you have to at least change out the optical interface.

> Either way, at some point, in the course of upgrading, it'll be
> necessary to "move" the fiber to a different box. While this is not as
> simple as splicing copper, I doubt that it'd be *that* expensive.

Actually, done right, it's easier than splicing copper; if done right,
the outside plant (OSP) fiber terminates in a splice tray and is
spliced onto a connectorized jumper; the jumper is then connected to
whatever equipment you want.  You want to change the equipment, you
move the jumper.  Of course, you have to coordinate things so you
don't bring the user down ...

Typical Disclaimer: I don't work with this stuff, and I never did at
AT&T, so I don't necessarily know what I'm talking about, and even if
I do, it's not necessarily what my company's position is.  Anywhere.
Ever.