Muni fiber: L1 or L2?

Sat Feb 9 00:43:47 UTC 2013

Jean-Francois Mezei wrote:

>> The problem of PON is that, to efficiently share a fiber and
>> a splitter, they must be shared by many subscribers, which
>> means drop cables are longer than those of SS.
> 
> Pardon my ignorance here, but could you explain why the cables would be
> physically different in the last mile ?

Drop cables are not for last miles, but for last yards.

Let's assume 4:1 concentration with PON.

Let's also assume that 1150 subscribers are evenly distributed over
51km trunk cable, which means distance between adjacent subscribers
is 44.3m.

> Why would this be different in a PON vs Point to Point system ?

If you use SS, you need a closure every 44.3m drop cable length
from which will be 5 or 10m.

 -C-------C-------C-------C-------C-------C-------C-  trunk cable
  |       |       |       |       |       |       |   drop cable
  S       S       S       S       S       S       S

                 S: Subscriber
                 C: Closure

OTOH, if you use PON and have 4 drop cables from an in-field
splitter, two drop cables needs extra 22.2 m and other two
needs extra 66.5 m.

 ------------C-------------------------------C-----  trunk cable
           || ||                           || ||     ^
 +---------+| |+---------+       +---------+| |+---  |
 |          | |          |       |          | |      | drop cable
 |       +--+ +--+       |       |       +--+ +--+   |
 |       |       |       |       |       |       |   v
 S       S       S       S       S       S       S

                 S: Subscriber
                 C: Closure

In this case, total extra drop cable length for PON is 51km,
identical to the trunk cable length.

It all depends how (initial and subsequent) subscribers are
distributed, but tendency is same.

As for cost for closures, while SS needs four times more
closures than PON, a closure for SS is simpler and cheaper
than that for PON to purchase, install and maintain.

> Wher I see a difference is between the neighbourhood aggregation point
> and the CO where the PON system will have just 1 strand for 32 homes
> whereas point to point will have 1 strand per home passed. But the
> lengths should be the same, shouldn't they ?

Never ignore topology at the last yards.

						Masataka Ohta