With Verizon ramping up deployment of gigabit passive optical networks this year, work is already well under way to develop successors to GPON. David Foote, chief technology officer for Hitachi Telecom USA, gave Telephony a view into that process.

On paths to next-gen PON: There are two general approaches, both in the standards bodies and among most vendors: the higher line rate, similar to current GPON but run at faster speeds like 10 Gb/s; the other is to run multiple wavelengths on the same fiber and use wavelength-specific filters at the [optical network terminals]. That could be either using DWDM or CWDM wavelengths, depending on how many wavelengths you want to run and the performance [you need]. Two standards bodies are working on 10G: The IEEE is working on an Ethernet or EPON flavor, and [Full Service Access Network] has started on a successor to 2.5G GPON at 10 Gb/s. There’s been some talk about trying to unify those standards, but that hasn’t progressed very far. Right now at least the optics or lasers used could be used for both technologies, even if the framing mechanisms and protocols are different.

It’s still early, but one general trend we see is more interest in 10 Gb/s GPON for business or enterprise services. There’s an expectation that GPON, because of the way it was standardized by FSAN and the ITU, is a little more stringent in meeting [service level agreements]. Also, GPON can support an embedded synchronization mechanism if you want to do something that requires synchronization like TDM-type emulation. We see the 10G flavor of EPON [more among] CLECs or [in] developing countries like China, where the service provider may not have lots of existing infrastructure or their main target is to get high-speed Internet to as many customers as possible.

On 10G PON: There’s a number of alternatives on how to do 10G. It depends on your confidence level in your optics and your assumptions about span design. If you want to maintain 20 km and 32-way splits, you’ve got to increase your launch power on 10G or have very good receiver designs that can handle signals with low receive levels. There’s going to be varying points of view from technology companies: increase power, reduce split ratios, shorten distances, have really good receiver designs (or combinations of those things) or go to parallel modulations. A lot of different approaches will be suggested, and it will boil down to: What’s your assumption of [outside plant] span design? Do you still think you have to meet 20 km and 32-way splits? That was driven very much by a North American model — typical suburbia. If you think your main markets are going to be high-density big cities in Asia or Europe, 32-way splits with 20 km may not make sense.

On hybrids: For example, running 2.5 Gb/s PON on, say, four CWDM wavelengths on the same fiber at the same time — technically there’s 10 Gb/s running on the fiber, but it’s four times 2.5. Most people in the standards bodies wouldn’t consider that true next-gen PON. NG PON is either 10G or DWDM PON. A lot of people consider running 2.5G on four wavelengths an interim step between current GPON and NG GPON. It’s a hybrid. You’d need to put wavelength filters at the ONTs. Whether you can add a filter to your current ONTs or will need to replace them depends on the design of your current ONTs.

On RF video: That’s one of the issues being debated in FSAN as they look at 10G. If your solution to 10G is to increase the transmission power at the [optical line terminal], you run into interference issues with [radio frequency] wavelengths. Will RF overlay still be needed at the point 10G GPON comes on the scene? I don’t know. Customers like to have options. Getting a customer to say, ‘I’ll never do another RF wavelength’ — customers tend not to be telling us that. But it has major implications for how you approach the cost of the technology. Verizon is still not very comfortable with IP video. How quickly will that change over time is the crystal-ball question. In a hybrid approach, RF overlay impacts the ONT and splitter designs; one of the wavelengths has to be reserved for RF. The IEEE is not considering [RF video] at all for 10G EPON.

On the timing of commercial NG PON gear: In 2010 you might start to see early products, with mass deployment in 2011 or later. WDM PON will probably be the same, if not further out. Hybrid 2.5 Gb/s gear is theoretically feasible now. You might see 2.5G hybrid approaches in the next year or two for niche applications — business parks or residential high-rises.

On DOCSIS 3.0 and NG GPON: I don’t think 3.0 is really driving interest in NG PON. What comes after 3.0 might drive a move to WDM. 3.0 creates at best parity with GPON, and that’s debatable.