Passive Optical Network (PON)

Sat Jan 21 21:22:20 UTC 2017

I evaluated several campus PON project on both vendor/provider and customer
sides over the last 5 years.

PON was designed as a last-mile technology for _operators_ to cover huge
areas and save on OPEX - that's the usual vendor's mantra.
GigE usually takes two fibers to deliver; GigE aggregation requires an
Ethernet switch you need to power and maintain - "many points of failure"
argument.
PON only takes one fiber, splitting a PON signal is done by a cheap passive
optical splitter which, once installed, lasts forever.

Correct cost comparison between PON and Ethernet is pretty difficult.
First, the cost of the actual network _equipment_ (switches, routers etc.)
for an Access network (tens of thousands of subscribers) is nothing
compared to the civil works - trenching, cabling, permits etc. Second, CPE
cost is the most sensitive on that scale. $5 cheaper CPE saves more money
than a $50k cheaper OLT.

Without scale benefits and (assumed) OpEx reduction, PON projects are
usually significantly more expensive.

Now, to the projects.
I have never heard of seen PON on a DC level.
As for the campus, none of the projects took off, and here is why:

- PON equipment is proprietary. An OLT (PON hub) from vendor X works only
with ONTs from the same vendor. Every other vendor claims there is "some
interop" but none was able to do demonstrate.
- PON infrastructure - a passive fiber tree - is a) proprietary b) not
flexible. You can make any physical topology of your usual p2p fiber
segments but a tree is always a tree; plus PON usually requires green APC
(angle polished) connectors.
- PON US/DS bandwidth allocation is asymmetric.

Training, maintenance and support are important, too. Ethernet is
ubiquitous, PON engineers are a bit harder to find. Proprietary nature of
the product implies that a Huawei PON would look and feel somewhat
different than, say, Calix PON hence the knowledge is more vendor-specific.
Also, nobody likes vendor lock. If an Access Ethernet switch fails, you can
- potentially - replace it with another fairly easily. PON ONT of different
vendors may all come from the same OEM like Cambridge but the firmware is
different.

What did I miss?... Ah, the usual cabling

There is a more sophisticated WDM-PON. Ericsson and Teradata had it in
development, Infinera offers it as iAccess product - but I haven't tried
that yet.

Overall, it really depends on a project (getting all the MTBF data and
calculating the failure cost was quite a task) but I personally can't see
any PON benefits over Ethernet for either campus or DC even in the midterm.

>From my personal experience, flexibility with cables plus cheap CWDM
filters and colored optics can do magic on the campus level.

Stas

On Sat, Jan 21, 2017 at 10:44 AM, Kenneth McRae <kenneth.mcrae at me.com>
wrote:

> Greeting all,
>
> Is anyone out there using PON in a campus or facility environment?  I am
> talking to a few vendors who are pushing PON as a replacement for edge
> switching on the campus and in some cases, ToR switch in the DC.  Opinions
> on this technology would be greatly appreciated.
>
> Thanks,
>
> Kenneth