Metro Core Development Trends:
ROADM Developments and Beyond

| Apr 11, 2008 | Optical Infrastructure | Advisory Report

| Analyst: Christina Howe Dietrich

Summary

Christina Howe Dietrich Senior Analyst, Optical Infrastructure

While vendors have been offering metro core ROADMs for several years, these elements have recently achieved a new level of maturity and overall market acceptance. Originally designed for long-haul networks, ROADMs have evolved in response to operators’ needs for reconfigurability in the metro and even edge networks. ROADMs have progressed from two-degree (single ring) wavelength blockers intended for long-haul solutions to multi-degree (up to ten directions of interconnection) wavelength selective switching devices optimized for metro deployments.

While metro core ROADMs may be more expensive and complex than their long-haul counterparts, operators, particularly in North America and Asia Pacific, have embraced them for their flexibility and ability to support changing traffic patterns and demands dynamically. Vendors’ development histories and carriers’ deployment experiences contribute to the newfound maturity of metro core ROADMs and position the devices for widespread adoption over the next several years. This report outlines the latest trends in metro core ROADMs and the market drivers that have caused this evolution from a novel, disruptive technology to a vital network element that is integral to carriers’ success.

Current Analysis Perspective

When metro core ROADMs debuted, the feature set was far from standardized. Depending upon the vendor, a metro core ROADM could be simple or complex, reflecting the uncertainty about how and when carriers would embrace this disruptive technology. Some vendors chose to keep it simple and developed low-cost, but also low featured, two-degree ROADMs designed for simple ring interconnect.

Alternately, other vendors became early adopters of wavelength selective switching (WSS) technologies for the foundation of their multi-degree ROADMs. The WSS-based ROADMs were more expensive but the technology allowed the ROADMs to support interconnecting multiple rings and hub locations, thereby enhancing network design flexibility in support of advanced services delivery and mesh architectures.

Both solutions achieved some level of carrier acceptance because operators had to contend with the trade off between functionality and cost. However, with bandwidth demands exploding in the metro and mesh topologies becoming more prevalent, operators have embraced the flexibility provided by metro core ROADMs. Vendors’ experience developing ROADMs and operators’ experience deploying ROADMs have resulted in a new level of maturity for the devices and, as a result, a more standard definition of the expected capabilities.

One of the most notable changes is that WSS-based ROADMs have now become table stakes for vendors targeting the metro core ROADM market. Practically every vendor attempting to address this market has a generally available WSS-based, multi-degree ROADM. The reasons why are relatively common in the product development cycle. First, costs have come down. Specifically, underlying WSS technology (achieved with MEMs or liquid crystal) has become more mature, more reliable, and able to withstand the environmental requirements necessary for widespread deployments. In addition, carriers are designing mesh metro networks with widespread interconnecting metro rings. Together these factors have driven carriers to indicate their preference for multi-degree ROADMs and the vendors have responded in turn.

As carriers offer increasingly sophisticated, bandwidth intensive services to customers, the capacity requirements for metro core devices are also growing. Consequently, 10 Gbps support (either OC-192/STM-64 or 10GbE) is ubiquitous among metro core ROADM devices. Going further, 40 Gbps support is emerging in anticipation that bandwidth requirements will continue to increase. Because the cost of supporting 40 Gbps signals is currently not low enough to justify widespread deployment, network operators are looking to utilize 40 Gbps interfaces in targeted applications including router interconnections and major network bottlenecks. As the economics improve, 40G is expected to become more prevalent in metro core ROADM devices. As a result, most ROADM vendors either are in the process of developing 40 Gbps interface cards or have already released this capability.

Another trend that has emerged during the maturity of metro core ROADMs is the inclusion of MSPP functionality on interface cards. The MSPP-on-a-blade functionality addresses carriers’ need to offer more types of services (including Ethernet services, OC-N pipes and entire wavelengths) within the confined space requirements of most central offices. Integrating this MSPP functionality into a metro core device flattens the metro network by combining the functions of multiple network elements into one.

From a carriers’ perspective, this implementation can result in lower CapEx by eliminating the need for multiple back to back network elements and/or interface cards, lower OpEx due to simplified maintenance and administration, and improved reliability by eliminating some cabling requirements between network elements. In addition, the ability to groom and aggregate lower speed signals maximizes the amount of traffic on a wavelength which, in turn, allows carriers to more efficiently utilize its equipment investment.

Beyond ROADMs, there is an emerging trend to pack more functionality into metro core platforms. When metro core elements were first introduced, they were relatively basic WDM devices designed to support increasing bandwidth demands by allowing carriers to maximize the amount of services transported using the existing fiber infrastructure. Then, as carriers began to offer more complex services, vendors developed ROADMs in response to carriers’ need for flexibility and dynamic reconfigurability in the metro network. Now, vendors are adding Layer 2 aggregation and switching (traditionally found in centralized routers) into their metro core devices to support carriers as they transition from TDM to IP based networks. In addition, metro core platforms incorporate comprehensive management and control mechanisms to simplify the increasingly complex operation of these network elements, and to better support deterministic Ethernet services. The combination of all of these features (multi-degree ROADM, MSPP, Layer 2 capabilities, intelligence and flexible WDM transport) represents the latest evolutionary stage for metro core devices. These new platforms encompass the functionality of several pieces of equipment (in essence collapsing the metro network), thus making the network simpler and less costly to scale. Some vendors are defining these “converged” solutions as packet optical platforms. Other vendors are using a less rigid definition, instead implementing a packet optical solution that encompasses a collection of platforms. Consequently, two camps are emerging in the packet optical arena: single box solutions and collections of optimized elements. There are pros and cons to both methods of supporting both legacy and newer IP services. However, there is no arguing about the considerable carrier interest in packet optical and the growing opportunity this area represents for optical vendors.

On the other side of the spectrum, vendors are also introducing smaller ROADMs for the metro network edge. This more recent development reflects operators’ desire for reconfigurability in more parts of the network. Increasing video and peer to peer traffic is driving up bandwidth requirements in the metro edge. By deploying ROADMs at the metro edge allows, carriers can keep local traffic in the edge network and avoid costly bottlenecks in the core network.

However, the functional requirements for metro edge ROADMs vary from their metro core counterparts. First, metro edge networks typically consist of individual rings subtending from the core network. Second, the metro edge typically consists of more network elements. As a result, ROADMs intended for the metro edge are smaller and less expensive than metro core ROADMs and typically support just two-degrees. In order to meet carrier demand for these new ROADMs, vendors may be able to leverage the development on metro core devices to modify the ROADM to edge applications. For example, Tellabs adapted its 7100 OTS platform to develop the 7100 Nano, a lower capacity, smaller two-degree ROADM, for metro edge applications. In addition, Fujitsu recently released a two-degree version of its ROADM for the FLASHWAVE 7500 to provide reconfigurability at smaller node sites in the core and edge networks. In conclusion, while metro core ROADMs are not novel network elements, they have achieved a new level of maturity and market acceptance.

Metro core ROADMs have evolved to support advanced capabilities, like multi-degree ring interconnections, and to integrate functions that expand the traditional definition of a metro core NE, including MSPP-on-a-blade, and L2 switching and aggregation capabilities often supplied by routers. These technical advances are receiving a positive reception from operators around the globe – although the pace of deployment varies among region. To this end, while the definition of a packet optical solution varies by vendor – some preferring “converged” (i.e., single box) solutions, while others attempt to “optimize” both carrier Ethernet and WDM transport pieces in separate, purpose built network elements – the clear implication is that metro core platforms will be an area of considerable growth and ongoing product development for some time to come.

Recommended End User Actions

• Service providers need to press Alcatel-Lucent on its ROADM plans. Even with the news that the 1850 TSS contains a “home grown” ROADM, the vendor still has three ROADM products in its catalog. Prolonged uncertainty over ROADM plans will damage the competitive position of Alcatel-Lucent in the ROADM market. As such, any carrier that has already made a commitment to any of the company’s current ROADM platforms, or that is considering doing so, needs to seek details from Alcatel-Lucent soon.

• Service providers that do not yet have the widespread need for multi-degree ROADM capabilities in their networks should seek details on the “hybrid” ROADM solution that Ciena features in its CN 4200 platform. Because the CN 4200 uses subwavelength grooming to simulate ROADM capabilities for line rates below 2.5 Gbps, the CN 4200 should appeal to the flexibility requirements of network operations below the 10 Gbps wavelength level.

• Carriers considering complex mesh metro networks should investigate ECI’s XDM ROADM implementation which supports up to ten degrees. Most vendors do not support this level of complex interconnection today. Consequently, while the number of applications requiring this may be small, ECI may be one of the only vendors that can provide this level of flexibility.

• Carriers need to evaluate the different packet optical solutions that are available today carefully. Some vendors that are investing heavily in packet optical are attempting to restrict the definition to converged solutions. However, there are the trade-offs between a single-box packet optical solution and a multiple platform implementation. Carriers may find that an intermediate approach supporting a mix of standard router and newer multi-functional devices best fits their needs.

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