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Ultra-Broadband

BBWF: WDM PON? Bring It On!

PARIS -- Broadband World Forum Europe -- WDM PON might not be set for mass commercial deployment for a few years yet, but when it is, expect to see it rolled out in Italy.

While the technology, which delivers a dedicated, secure wavelength to each end user, has had some limited deployments (especially in Korea), it's not due to be standardized "until at least 2012, and most likely later," notes Heavy Reading chief analyst Graham Finnie in his recent report, "FTTH Review & Five-Year Forecast: The Road to Next-Gen PON."

But Telecom Italia (TIM) CTO Stefano Pileri, who made a keynote presentation on "Network and IT Renaissance" here in Paris, is excited by its capabilities.

"WDM PON... [is] a good technology that's coming. It's good for capacity, and it allows the virtual unbundling of the fiber," noted the Italian, who is keen to cut down on the number of central offices/local exchanges that are housing broadband equipment in Italy's cities.

And that's one of the reasons he's keen on WDM PON -- it requires very little in the way of above-ground physical space, even in large cities. It's also why he is not so keen on the point-to-point fiber access alternative that has already proved popular elsewhere in Europe, including Italy, courtesy of Fastweb SpA (Milan: FWB) -- so far.

"I don't believe in fiber point-to-point because we need to reduce the number of central offices we have," and point-to-point FTTH involves housing large-framed equipment in multiple locations, noted the CTO.

That opinion is likely to be shared by many incumbents, and will be music to the ears of the vendors already talking up WDM PON's potential. While the likes of Alcatel-Lucent (NYSE: ALU), Ericsson AB (Nasdaq: ERIC), and Huawei Technologies Co. Ltd. are focused on promoting other flavors of PON (though all have WDM PON in development), ADVA Optical Networking , Nokia Networks , and LG-Ericsson Co. Ltd. are already vocal supporters, with LG-Nortel talking up some early but small deployments. (See LG-Nortel Shows Off at BBWF, LG-Nortel Extends WDM-PON Distribution, and WDM-PON Update.)

The pitch from NSN, which has abandoned its own GPON developments to focus on VDSL2 opportunities and the future potential of WDM PON, is right on Pileri's wavelength. (See Nokia Siemens Dumps on GPON.)

Talking during a media and analyst briefing here this week, the vendor's CTO, Stephan Scholz, said that WDM PON is the technology that can "unlock the potential of FTTH" and "eliminate the central office... all of Paris could be covered with just one site."

He said NSN will have a prototype unit soon that will demonstrate 1 Gbit/s per wavelength over a distance of 100 kilometers. He expects to have pilots with operators in 2011 or 2012, and commercial products in 2013.

That's some way down the line, though. In the meantime, Telecom Italia is deploying a mix of high-speed fixed broadband technologies and architectures, including fiber-to-the-curb (FTTC) with VDSL2 copper tails, fiber-to-the-building (FTTB), and some FTTH using GPON.

— Ray Le Maistre, International News Editor, Light Reading

digits 12/5/2012 | 3:56:47 PM
re: BBWF: WDM PON? Bring It On!

It seems to me that an incumbent such as Telecom Italia would face some very high regulatory hurdles if it planned to close/sell the vast majority of its central offices. It's an interesting idea, though.


If WDM PON can be shown to be stable, secure and affordable, it's going to be a tough technology to bet against.

Duh! 12/5/2012 | 3:56:44 PM
re: BBWF: WDM PON? Bring It On!

The biggest regulatory hurdle is going to concern trenching:  they can hardly put a shovel in the ground in most of Italy without having to bring in an archaeologist.  So the first and most obvious question is whether they have the capital and the stomach to do anything involving new fiber infrastructure, especially since doing so will be extra expensive in the interest of protecting their (our!) cultural heritage.


As far as WDM PON is concerned... it's not clear from the context whether they mean a wavelength-per-subscriber type approach like LG-Nortel and ADVA, or more of a hybrid WDM/TDM approach, with integrated access and backhaul, as in the IST-PIEMAN project.  If they're talking about CO consolidation, it would probably be the latter.


So if we assume that, there would be trade-offs between three possible approaches:


1) amplified (or regenerated) GPON with 128 subs per backhaul/feeder fiber, and high count cables in the backhaul.


2) hybrid WDM/TDM, WDM and amplification in the hub (ex-CO) location and colorless ONT


3) hybrid WDM/TDM, wavelength translation (either OEO or 4-wave mixing) and amplification or regeneration in the hub, and standard GPON ONT.


The key points of the trade-off are going to be initial cost of civil works and hub opto-electronics, cost of ONTs in volume, reliability/availability/maintenance and power. 


1) is going to involve SOAs in the hub, which are still pricey -- but more for lack of volume than for process concerns -- and are shared equipment.   Cost of additional fiber strands is nominal compared to cost of duct.  Of course if they  are  planning to use existing fiber, this approach will be self-limiting.   GPON ONT costs have been pushed down the cost curve.  


2) involves colorless ONTs.  The most likely approach will involve RSOAs, which are quite expensive and need to be cooled.  The hub can use EDFAs. 


3) can involve protocol aware OEO regenerators/wavelength translators in the hub.  There are timing issues with this, although they can probably be overcome with enough complexity.  Alternatively, all-optical wavelength translation, probably with 4-wave mixing can be used in conjunction with optical gain stages.  This is not yet mature technology.  But at least GPON ONTs can be used.


Someone would have to do some serious modeling based on their network design and supplier pricing to figure out the trade-offs.


As far as unbundling is concerned, WDM unbundling would be an expensive mess.  They'd have stranded cost all over the network (in the form of equipped wavelengths with one or two subscribers), plus risk of interference between operators' equipment. The only clean way to do unbundling is at the VLAN level, as OpenReach proposed to the UK regulators a couple of years ago.

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