Multidegree ROADMs take center stage

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The industry has been buzzing about reconfigurable optical add/drop multiplexers (ROADMs) since SuperComm 2004, which proved to be a coming out party of sorts for the technology. Today, a new class of ROADMs has people talking-specifically, multidegree ROADMs with wavelength-selective-switch (WSS) technology. The vendors have announced product, and for North America’s biggest carriers, Verizon and AT&T, that product can’t come fast enough.

Early ROADM implementations were based on wavelength blockers, which block selected wavelengths from passing through a node, then direct those wavelengths to an optical filter where they are dropped from the transmission stream. This architecture requires that all wavelengths are sent to the node, even if only a subset of those wavelengths will be terminated there. Emerging WSS-based multidegree ROADM architectures, by contrast, support meshed network topologies and enable any-port-to-any-port interconnectivity.

WSS-based multidegree ROADMs are so new, in fact, the industry has yet to adopt a common set of terms to describe them. Verizon, for example, uses the terms “WSS” and “multidegree ROADM” interchangeably, while AT&T prefers the term “photonic crossconnect,” arguing that WSSs are a component or subsystem within a ROADM, and ROADMs could be built using other technologies, such as wavelength blockers.

Moreover, “multidegree ROADM does not necessarily imply full, 100% crossconnect connectivity,” notes Pete Magill, director of AT&T Labs (San Antonio, TX). “We like to use the term photonic crossconnect because it implies that all directions coming in are equal and can be switched from one to another freely.”

Verizon initially deployed ROADMs in its ultralong-haul system “to reduce the cost per megabit per mile. It was really that simple,” reports Stewart Elby, vice president of network architecture and enterprise technologies. ROADM price points two years ago were such that Verizon could prove in the equipment on a cost-savings basis in the long haul. Over the last two years, innovation and competition have driven ROADM prices down even further, to the point where a carrier like Verizon can deploy ROADMs economically in the metro as well, says Elby. In Verizon’s metro network, there is one key driver: video.Th 210698

Vendors like Meriton Networks now incorporate multidegree ROADM functionality into their transport platforms, such as Meriton's 6400 OTP, to enable carriers to deploy mesh networks that support less predictable video traffic.

Industry insiders agree that ROADM technology doesn’t prove in for sub-10-Gbit/sec metro applications. In fact, Jason Marcheck, principal analyst of optical infrastructure with Current Analysis (Sterling, VA), believes the uptake of 10-Gbit/sec wavelengths in the metro will determine when, how fast, and how much ROADM deployments will increase in the metro. However, the folks at Verizon don’t need a crystal ball to tell them when this crossover point will occur. Thanks to its FiOS video service, now offered in parts of seven states, Verizon has crossed the 10-Gbit/sec threshold-and then some. “The video is just sucking up 10 gigs,” reports Elby. “The granularity is still at the gigabit layer, but the aggregate that has to get between offices is multiples of 10 gig.”

To handle the additional bandwidth requirements and increasingly unpredictable traffic patterns associated with video delivery, Verizon issued an RFP specifying a multidegree ROADM. “We called it a ROADM when we did the RFPs originally because that’s what the industry was geared up about, but having something that’s only degree two-a ring-wasn’t proving in,” admits Elby. “We needed to get to degree four, degree six, degree eight. Our ultralong-haul product is doing that, and the product that we are about to announce for the metro does that as well. We need a box that can be a ring for some applications, but we’d like the same product to have upgrades or add another card into the chassis and be able to get to higher-degree switching.”

The terminology differs from carrier to carrier, but Verizon talks in terms of hub offices and super hubs, and this is where the eight-degree ROADM makes economic and functional sense. Collector rings supporting SONET and next-generation SONET transport come together in hub offices in the metro network, and those hub offices then are interconnected through a set of super hubs. The fiber routes themselves are on the order of four and eight degrees, says Elby. Supporting these routes via legacy architecture requires stacking back-to-back ADMs with broadband digital crossconnects between them-which is expensive and requires a plethora of jumper cables in the central office.

“Replacing all of that with a degree-four, degree-six, degree-eight ROADM or WSS and including integration of ADM on that same platform, which is what we’ve required-we call it ADM on a wavelength-allows us to grow the network in a way where you put in basically a single a platform with these cards as opposed to putting in four or five platforms that then have to be interconnected within the CO,” explains Elby.

Some industry insiders view eight-degree ROADMs as the endgame of a long-term migration path, but when asked when Verizon hopes to deploy eight-degree ROADMs, Elby responds, “As quickly as we can.” He notes that there are still some problems with yield on the eight-degree ROADM chipsets, but he fully expects those manufacturing issues to be resolved and production to commence by the end of the year.

Though not as far along in its video service delivery plans, AT&T nevertheless is planning for the increased bandwidth and unpredictable traffic requirements that mark a video service. Its metro network, particularly the old SBC footprint, consists of many stacked rings that may be homing in on the same buildings or facilities.

“There’s a need to have more optical add/drop nodes on a ring and maybe even be able to get traffic off a smaller subtending ring and onto a bigger ring and then off to another subtending ring,” explains Mark Feuer, senior technical specialist, AT&T Labs. “When you start to piece together these more complicated networks than just simple rings or simple point-to-point connections, then the multidegree starts to become more important.”

Moreover, Feuer reports that AT&T also is crossing the 10-Gbit/sec threshold in its metro network. “10-gig is rapidly becoming the standard rate of choice,” he says. “It really is present-tense and growing rapidly.” Maybe not directly to the customer yet, he admits, but once AT&T starts aggregating video traffic in the network, 10-Gbit/sec wavelengths will be the norm.

Like Verizon, AT&T also believes there is a need for up to eight-degree mesh networking in the future. Consider the so-called NFL cities, says Feuer. Most of those cities have fiber coming in and out in two places, either north and south or east and west, and a two-degree ROADM would be sufficient. But some cities might have fiber coming in from three or four directions, which would require three- and four-degree photonic crossconnects.

“A lot of people felt like [four degrees] was sort of the limit for high-degree nodes-only at those places where, because of geography, you happen to have enough traffic coming in and out of different places,” notes Feuer. “But as part of some of our own research and looking into our networks and the way we want to build robust systems and allow future growth, we can clearly see that you really need to have more like six-, seven-, and eight-degree nodes in the future.”

While he cannot predict exactly when an eight-degree ROADM might prove in from an economic standpoint, Feuer admits that “if you want to have a photonic network where all the wavelengths can come and go between all those cities easily, you will really need to have the higher-degree nodes in the not-too-distant future.”

With the anticipated increase in video-on-demand (VoD) traffic-The Yankee Group (Boston, MA) expects VoD revenue to top $171.4 million in the U.S. by 2009-vendors are scrambling to ready their devices. A number of vendors already have announced multidegree ROADM products and projects.

Meriton’s (Ottawa, ON, Canada) 6400 Optical Transport Platform (OTP), for example, features WSS-enabled multidegree ring support. Movaz Networks (Atlanta, GA) has both two-degree and multidegree ROADMs using MEMS-based WSS technology; Fujitsu (Richardson, TX) has added WSS-enabled eight-degree reconfigurability to its FLASHWAVE 7500; and Tellabs (Naperville, IL) has introduced new WSS-enabled four- and eight-degree ROADM capabilities for its 7100 optical transport system. Cisco (San Jose) recently introduced a two-degree ROADM card for use in its ONS 15454 product, and NEC America (Irving, TX) has added multidegree support for its WSS-enabled SpectralWave 4200. Ciena, meanwhile, has begun talking about its WSS-based dynamic wavelength-routing technology and will likely make a product announcement later this year.

The recent merger between Lucent (Murray Hill, NJ) and Alcatel (Paris) should affect the competitive landscape as well. Lucent resells Movaz’s RAY-ROADM equipment-and used it to nab a high-profile ROADM win in Verizon’s long haul network. Alcatel resells Tropic Networks’ (Ottawa, ON, Canada) TRX-24000, which provides multidegree support using wavelength blocker technology.

“Although both products have their strong points, the reality is that it probably will not be feasible to keep both partnerships intact,” admits Marcheck, who adds that “once the merger is completed, [Alcatel and Lucent] should pick a single ROADM partner-and perhaps even consider buying that company.”

For his part, Marcheck cautions that it may be too early to count out wavelength-blocker technology. If prices don’t come down for WSS components, wavelength blocking could remain relevant for quite a while, he says, particularly in the lower-degree implementations.

Blocker-based or WSS-based, multidegree ROADMs seem to be on everyone’s roadmap. “ROADM has become a must-have requirement in the network now, compared with early/mid-’05 when it was simply a nice-to-have,” contends Bijan Khosravi, chief executive officer of Movaz Networks. “I have not seen a single proposal in the last three months that does not require ROADM, either immediately or within 12 months.” He admits that he expected a little more conservatism on the part of the service providers, but “they are really buying it, deploying it, and accepting the technology.”

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