Muni fiber: L1 or L2?

Jean-Francois Mezei jfmezei_nanog at vaxination.ca
Sat Feb 2 05:22:07 UTC 2013


On 13-02-01 22:52, Owen DeLong wrote:

> Since the discussion here is about muni fiber capabilities and ideal greenfield
> plant designs, existing fiber is irrelevant to the discussion at hand.

Not so irrelevant.  If the municipality wishes to attract as many
competitive ISPs as possible, it wants to build a "standard" last mile
that ISPs can easily interface to. One which is compatible with other
FTTH systems.

Currently, the standard is GPON (even though there are many variations
to the theme).

Sone may say that having L1 service with each ISP having their OLT with
splitters at the CO is an advantage. It also means that each ISP has to
have its own ONTs in homes and they can all choose different configs for
OLTs and the light in the fibre. Greater flexibility to differentiate
between ISPs. (one may choose RFoG for TV with DOCSIS for data while the
other is an all data link with  IPTV.)

But for an end user, switching ISPs would mean switching the CPE
equipment too since the ONT installed by ISP-1 may not be compatible
with OLT used by ISP-2.

Requiring an ISP to have its own OLT at the CO with its own splitter
also raises startup costs and reduces the chances of having competitive
ISP environment.

Providing L2 service means that ISPs connect to a municipal OLT, so they
do not have to purchase OLTs and bother with splitters. At that point,
it si simpler and cheaper to deploy splitters in neighbouhoods. It also
reduces number of splices.

When you do 1:1, you may have a big cable with lots of strands leaving
the CO, but you'll have a JWI in neighbouhood where you cross connect
the strands from CO to the strand that uses the pre-fab cable to the
backyards of homes served.

So in all the calculations made on dB loss, the number of splices was
not factored in. You're not going to get a continuous cable from the CO
to the telephone pole behind a home.  If you put the splitter at the CO
you get the losses from the splitter, and then losses from a splice at
the neighbouhood where trunk from CO connects to cables that runs
through backyards.

When you put the splitter in the neighbouhood, it performs both the
splitting and the connection of the cable from CO to the backyards. So
you eliminate one splice.






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