FTTH Active vs Passive

William Herrin herrin-nanog at dirtside.com
Tue Dec 1 11:33:03 CST 2009

On Tue, Dec 1, 2009 at 11:43 AM, Justin Shore <justin at justinshore.com> wrote:
> Luke Marrott wrote:
>> I'm wondering what everyones thoughts are in regards to FTTH using Active
>> Ethernet or Passive. I work for a FTTH Provider that has done Active
>> Ethernet on a few networks so I'm always biased in discussions, but I
>> don't
>> know anyone with experience in PON.
> Active is the way to go.  Passive is merely a stepping stone on the way to
> active.  Passive only makes sense (in some cases) if you are 1) fiber poor
> and 2) not doing a greenfield deployment.  If you have the fiber to work
> with or if you are building a FTTH plant from scratch go with active.  The
> only real proponents of PONs are the RBOCs who are exceedingly cheap, slow
> to react, and completely unable to think ahead (ie, putting in an abundance
> of fiber for future use instead of just enough to get by) and some MSOs who
> don't dread and loathe shared network mediums like CATV and PON (whereas
> those from a networking background would never ever pick such a technology).


The suburban area where I live, mostly detached homes, has a service
density of around 1500 to 2000 residences per square mile. Practically
speaking, one or two dedicated fibers per residence at that density
means you're not going to get a 5 mile radius from your powered
equipment. Pi *  5^2 * 2000 residences * 2 strands per residence =
300,000 strands of fiber.

So you're going to deploy powered equipment to one hell of a lot of
non-customer field locations. Since most of those locations are not
carefully conditioned computer rooms, you're going to pay more for
ruggedized equipment too.

In that scenario, PON cuts the number of field locations in which you
have to maintain non-CPE powered equipment by an order of magnitude or
more. Perhaps even to zero. This improves system reliability and
yields a rather substantial savings on maintenance cost over time. Pi
* 5^2 * 2000 residences * 1 strand / 16 residences per strand = 9,800
strands of fiber, a much more manageable number.

Bill Herrin

William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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