Thanks to a bit of lateral thinking, Alcatel-Lucent has come up with a way to lower the initial cost of deploying TWDM-PON, which should make it easier for operators to consider adopting the latest in fixed-line broadband technology.
Time- and wavelength-division multiplexed PON is the approach chosen for the next generation of passive optical networks. Announced in October 2014, Alcatel-Lucent’s TWDM-PON system was the first on the market. It delivers 40Gb/s of capacity via four 10Gb/s transmitters, each on a different wavelength.
TWDM-PON requires new optics capable of tuning between these four 10-Gb/s wavelengths. But Alcatel-Lucent acknowledges that this flexibility comes at a price. Tunability adds complexity, which increases the price of the optics. With these optics not yet available in large quantities, TWDM-PON’s current cost is higher than that of more established technologies.
Alcatel-Lucent’s solution, which it calls Universal TWDM-PON, is to swap out the tunable optics and replace them with the fixed-wavelength optics used in 10G PON systems. Operators can use pluggable XFP modules designed for 10G-PON (or XG-PON1 as it is also known) or 10G-EPON commercial systems. These transceivers have not been deployed in huge volumes either, but they are less expensive than TWDM-PON optics simply because they are not tunable.
The wavelength of the fixed 10G optics is different from that specified in TWDM-PON, but this is not an issue, according to Ana Pesovic, senior marketing manager for the wireline division at Alcatel-Lucent. TWDM-PON has been designed to be backwards compatible with the PON technologies that preceded it, so all the wavelengths can coexist.
“It’s just a matter of using a different wavelength, everything else is TWDM-PON,” she said.
When operators want to move to a system with full flexibility, then they can just add a line card based on a tunable transceiver - they don’t even have to discard the fixed optics-based line card. This enables a ‘pay-as-you-grow’ upgrade path for service providers, the vendor says. The smooth upgrade to full TWDM-PON avoids the need to replace network components, evaluate new technology, or reconfigure operations and business support systems (OSS/BSS).
“You add the new optics and you have to validate the optics, that’s all,” said Pesovic. “In the future we think it will be plug and play but for now we are being cautious and advising customers to validate the transceivers.”
In contrast it can take up to one year to validate a new set of hardware, she says. By moving to Alcatel-Lucent’s Universal TWDM-PON now, operators can take advantage of XG-PON1 prices today, while the platform is ready for full TWDM-PON tomorrow.
Alcatel-Lucent is keen to point out that this doesn’t mean wavelength tunability isn’t on the industry roadmap any more.
“Wavelength agility is a mandatory requirement of next-generation PON. Every OLT [optical line terminal] has to have this capability otherwise the costs to operate and maintain the network would become unmanageable,” Pesovic explained.
She outlined a number of scenarios where an operator might wish to reassign wavelengths at the OLT: to add more capacity on the network by moving a group of end-users onto a new wavelength; to switch end-users from one operator to another on an unbundled network; in the case of a line card failure; or even to save electricity overnight by switching all the active consumers onto the same line card.
Some of these scenarios are firmly in the future, however. “Having spent all this time convincing you that this wavelength agility is important, it is not so important to the early adopters,” she laughed. “I don’t think many operators are waiting for dynamic management and tunability. The initial use cases are all for fixed wavelengths.”
Pesovic says that about 20 potential customers have tested Alcatel-Lucent’s TWDM-PON system - which is supported by the 7360 Intelligent Services Access Manager FX platform - and almost as many are in the pipeline to trial the system over the next few months.
“Some of them are going to start with this approach [Universal TWDM-PON] if not most of them,” she said. “The level of interest is quite overwhelming.”
Julie Kunstler, principal analyst, intelligent networks, with Ovum, commented: “TWDM-PON is an excellent upgrade for broadband providers, supporting recent, strong demand for residential gigabit services and expanding business/enterprise services. Operators can quickly add capacity in their broadband access networks and completely bypass 10G PON. In Universal TWDM, Alcatel-Lucent has developed an ingenious solution to help operators shrewdly manage their network investments and move directly to TWDM.”