Muni fiber: L1 or L2?

Fri Feb 1 03:48:16 UTC 2013

On Jan 31, 2013, at 19:21 , Scott Helms <khelms at zcorum.com> wrote:

> Fletcher nailed it, if you want the architecture you're describing then you simply don't want PON.  Its built around lower cost and a big part of that lower cost is minimizing the fiber costs by serving splitters (and thus many homes) from a single fiber that back hauls to the CO.  The other reason PON won't work for what you want is the splitters are passive and completely static in their operation.  Here's an image of one that may make this clearer:
> 
> http://media.wholesale-electrical-electronics.com/product/imgage/Electrical&Electronics/2010101220/6dc7c82d59d9fd931bfba560a3e85031.jpg
> 

I know what a splitter is and how they work. I understand PON really quite a bit better than you imagine I do.

Bottom line, you've got OLT -> FIBER(of length n) -> splitter -> fiber-drops to each house -> ONT.

All I'm proposing is making n really short and making "fiber-drops to each house" really long.
I'm not proposing changing the fundamental architecture. Yes, I recognize this changes the economics and may well make PON less attractive than other alternatives. I don't care. That's not a primary concern. The question is "can PON be made to work in this environment?" It appears to me that it can.

It will work as I've described, but, yes, it's very suboptimal from a cost perspective if your only goal is to deploy PON for a single provider.

If, OTOH, your goal is to have a fiber infrastructure in the neighborhoods that can support a multitude of possible services of which PON from a number of providers is just one such possible service, then, the PON operators can, in fact, install in the MMR and do the splitting at the MMR end of the subscriber fiber with home-runs from the MMR to each home.

True, PON is probably not the best technology fit for this. Ethernet probably makes more sense in most cases. However, if you have providers that do PON everywhere else and they don't want to support "exception equipment" for your facility, then it allows them to install PON just like their other deployments, only the splitter is next to the OLT instead of out near a collection of ONTs.

> If you have to either run several (or more) fibers to a neighborhood or have managed neighborhood elements then you've simply destroyed the use case for PON.  Luckily this use case matches pretty exactly for Ethernet, but you must do your wholesale play at layer 2 IMO to work economically.
> 

I disagree.  If you have home-run fiber to a large bank of patch panels in an MMR that can serve a ~8km radius of subscribers and providers can colocate whatever L2+ equipment they want to in said MMR with said fibers available for lease on equal footing to all providers, then the providers can deploy whatever makes the most sense to them whether that's SONET, Ethernet, PON, or optical tin cans over your fiber-string.

Yes, this is more expensive for the fiber deployment than running FTTH from the local BBox and having splitters in the BBox, but if it's being done intelligently, especially in areas of greenfield deployment, then it doesn't have to be a lot more expensive.

I get roughly 201 Sq. Km. as the area of an 8km radius circle (For the metrically challenged, that's roughly 77 Sq. Mi. or an area a little larger than Washington DC (68.3 sq. mi according to wikipedia).

If you're willing to require more expensive optics, you could go to a larger area served to accommodate lower population densities and for higher density areas, it might make economic sense to make the service radius smaller and have more centers. I don't know what the economically ideal subscriber volume per center would be. That would have to be calculated.

Owen

> 
> On Thu, Jan 31, 2013 at 6:28 PM, Owen DeLong <owen at delong.com> wrote:
> 
> On Jan 31, 2013, at 13:57 , Fletcher Kittredge <fkittred at gwi.net> wrote:
> 
>> 
>> 
>> 
>> On Thu, Jan 31, 2013 at 4:36 PM, Owen DeLong <owen at delong.com> wrote:
>> If you have an MMR where all of the customers come together, then you
>> can cross-connect all of $PROVIDER_1's customers to a splitter provided
>> by $PROVIDER_1 and cross connect all of $PROVIDER_2's customers to
>> a splitter provided by $PROVIDER_2, etc.
>> 
>> If the splitter is out in the neighborhood, then $PROVIDER_1 and $PROVIDER_2
>> and... all need to build out to every neighborhood.
>> 
>> If you have the splitter next to the PON gear instead of next to the subscribers,
>> then you remove the relevance of the inability to connect a splitter to multiple
>> OLTs. The splitter becomes the provider interface to the open fiber plant
>> 
>> Owen;
>> 
>> Interesting.   Do you then lose the cost advantage because you need home run fiber back to the MMR?   Do you have examples of plants built with this architecture (I know of one such plant, but I am hoping you will turn up more examples.)
>> 
> 
> I don't know of any. Yes, it would eliminate part of the theoretical cost savings of the PON architecture, but the point is that it would provide a technology agnostic last mile infrastructure that could easily be used by multiple competing providers and would not prevent a provider from using PON if they chose to do so for other reasons.
> 
> Owen
> 
> 
> 
> 
> -- 
> Scott Helms 
> Vice President of Technology 
> ZCorum 
> (678) 507-5000 
> -------------------------------- 
> http://twitter.com/kscotthelms 
> -------------------------------- 