Optical Switching Migrates to the Metro Network
By: Scott Clavenna, <%=company%>
It seems difficult to believe, given the rather sluggish uptake of metro dense wavelength division multiplexing (DWDM) by carriers in 1999, that in May 2000 a number of vendors would announce optical cross-connects for the metro market. The initiatives may smack of technology push, but metro networks pose compelling reasons for optical switching, albeit for different reasons than the evolving long-haul space.
Optical switches will manage the massive capacity that must be deployed to support new services in the metro network. Pioneer Consulting forecasts growth for the regional and metro optical switching systems market from $24 million in 2000 to $3.7 billion by 2004 (see Figure 1).
The metro optical switch market includes two main classifications of optical switching systems: "Opaque," meaning those that perform 3R (reshape, retime, regenerate) functions and switch optical circuits electronically, and "transparent," or those that perform all switching in the optical domain. The market also covers the entire range of service providers, including incumbent and competitive local exchange carriers (ILECs and CLECs), integrated communications providers (ICPs), and national carriers expanding into metro markets.
Long-haul legacy
In the long-haul space, the deployment of DWDM drives the emerging optical switching systems market. As the deployment of DWDM systems continues, the requirement for managing a large number of wavelengths within major hubs and points-of-presence in carrier networks becomes paramount to cost-effective network operation. Optical switching systems allow carriers to support optical layer restoration, while creating new optical layer services, such as optical virtual private networks and dynamic, reconfigurable, "wavelength services."
Both opaque and transparent optical switches have a role in the long-haul network, endorsed enthusiastically by major network operators, including Williams, Qwest, Extant, iaxis, and Storm. For reasons of commercial availability, opaque optical switches lead the market, but transparent optical switching systems are on the way from Lucent, Nortel/Xros, Chromisys, and Corvis. The systems offer the value of protocol and bit rate transparency, making them highly scalable and useful for restoration and network reconfiguration tasks.
Metro migration
Long-haul network evolution offers insight into the metro market. With very little WDM deployed (or OC-192, for that matter) in metro networks, it is difficult to envision widespread requirements for optical switches. But the switches are coming.
Sorrento Networks has announced its TeraMatrix photonic switch, which scales from a 4x4 configuration to 512x512 using two different types of switching matrices. Network Photonics, a recently minted start-up, is also targeting the metro market with an all-optical switch. Rumor has it that at least two more start-ups are developing all-optical switches for the metro market.
At first glance, a flurry of start-ups developing metro optical networking products on the heels of a maturing long-haul market may seem like a classic case of technology push. But a few compelling reasons pull these developments along: Enterprise access, dynamic optical add/drop, and ring interconnection.
Compelling metro switching needs
The metro market is radically different from the long-haul market, so the need for optical cross-connects and switches won't ever be the same. While matrix size and line rate support are important equipment attributes for long-haul networks, protocol transparency is paramount to metro network needs.
One of the most vital and underappreciated aspects of the metro WDM market is the enterprise access market. WDM systems in this space interconnect major corporate data centers with remote locations, offsite storage facilities, or data warehouses. ESCON, Fibre Channel, and Gigabit Ethernet are the primary drivers behind these deployments, because without DWDM they consume a single fiber for each connection.
ADVA, the dominant provider of enterprise WDM systems, has many installations that require more than 100 connections between two sites, making WDM essential to preserving fiber resources. Many major corporate users are asking for high-capacity private lines, including OC-12 (622 Mb/s) and OC-48 (2.5 Gb/s). None of these services fit well into traditional synchronous optical network (SONET)-based metro networks, making them a clear play for WDM systems. ADVA has recently made a strategic investment in OptXCon Inc., a startup developing an all-optical switch for metro networks.
Dynamic OADM
As the enterprise market evolves, Gigabit Ethernet and Fibre Channel will play an increasingly important role in all facets of metro optical networks. That said, metro optical cross-connects, if affordable, could provide dynamic reconfigurability of metro enterprise networks, with optical layer survivability.
In the reconfigurability/survivability scenario, the optical switches are deployed as highly dynamic optical add/drop multiplexers (OADMs) with a greater degree of functionality than existing products. Dynamic OADM functionality is a key aspect of metro optical switches. Agilent's recent announcement of a low-cost "bubble" switch matrix is well-suited for these applications and will be appearing in products in 2001.
The first two arguments for metro optical switching, enterprise access and dynamic OADM, favor all-optical switch solutions because they leverage the optical network's protocol transparency and flexibility. The third argument, ring interconnection, will likely favor opaque optical switches, but the case is not as clear as it is for the other two reasons.
Ring interconnection
As carriers seek to provide more high-bandwidth private line services and optical VPNs, ring interconnection will become important in metro optical networks. Provisioning high-bandwidth circuits across multiple rings is a difficult, if not impossible, process in many metro networks today.
Vendors are responding to the need for ring interconnection with customized, scaled-down versions of their long-haul switching systems. Ciena has just announced its metro-optimized optical switch, the Core Director CI, which is a lower-priced, smaller-scale (64 port) version of the CoreDirector, optimized for ring interconnection and STS-1 (52 Mb/s)-level grooming at the network edge. Other vendors will no doubt follow suit in the coming year.
In deployment scenarios for ring interconnection, optical switching systems operate as SONET switches, providing a platform for integrated management of optical circuits spanning multiple rings. These switches will support automated provisioning of OC-n circuits in the metro area, while supporting varying levels of restoration, such as SONET ring (UPSR or BLSR), diversely routed 1+1 protection, or ultimately mesh-based protection using datacom routing protocols.
Though it has yet to emerge as a truly vital market segment, the metro market for optical switches is important to consider. In the year 2000, at least a dozen vendors will bring multiservice platforms to market that make the most efficient use of SONET bandwidth or completely redefine metro networking with IP-based solutions. These new solutions will fuel competition among metro area service providers and quickly place new demands on the core of both the long-haul and metro networks.
In the next two years, optical switch deployments in the long-haul arena will garner most of the attention (and the revenue) of the market, but the metro market remains the sleeping giant, and optical switches will be a critical part of its awakening.