Selective WDM runs high-, low-speed metro traffic over shared fiber ring

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The introduction of dense wavelength-division multiplexing (DWDM) technology into the metropolitan market appears to have its share of proponents and skeptics. While legitimate bandwidth needs exist in limited portions of the market, most metropolitan customers remain reluctant to incur additional expense for bandwidth they may never really need. This situation presents a dilemma for service providers that must accommodate varying requirements while still offering an attractive package to new subscribers.

Chromatis Networks Inc. has developed one solution, called selective WDM (SWDM), that promises metropolitan service providers and their customers the best of both worlds. The new technology enables carriers to deliver multigigabit capacity to sites that require it, while allowing other sites on the same metropolitan ring to share less-expensive bandwidth not based on DWDM. Additionally, carriers can upgrade, as needed, to DWDM capacity in less time and at a lower cost.Th Acf41f

Chromatis Networks lets carriers satisfy the varying needs of metropolitan customers with selective WDM, a solution for delivering scalable bandwidth on an as-needed basis.

"To achieve fast turnup of services, a standard DWDM ring system requires every site to add or drop at least one wavelength as an entry-level configuration," says Rafi Gidron, chairman and co-founder of Chromatis. "That's fine for sites needing high bandwidth, but overkill for most traditional applications. The other alternative is to deploy DWDM systems on an ad hoc basis, which means time and effort to engineer and install new boxes in response to demand. SWDM economically supports lower bandwidth applications, but allows instant upgrade to DWDM capability with module adds at a fraction of the cost of an entire DWDM system."

Chromatis's SWDM solution is geared toward a metropolitan market that is in a state of flux in the wake of the 1996 Telecommunications Act. Multiple service operators and carriers are aggressively competing to capture a share of the market, but a problem exists in the variation of network requirements for site-to-site. Chromatis contends that one central office or head-end may serve large enterprises or Internet service providers (ISPs) with heavy data demands requiring OC-12 (622 Mbits/sec). Another might serve a residential area where broadband uptake is slow and a T1 (1.554-Mbit/sec) or DS-3 (44.736-Mbit/sec) connection can easily accommodate traffic.

Traditional transmission technologies that share a less-expensive Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) ring are sufficient for lower bandwidths, considering conventional DWDM systems require carriers to deliver at least one multigigabit wavelength to each site to drop or add network traffic. At the same time, some applications already have DWDM-level requirements and anticipate the need for additional DWDM capacities in the future.

SWDM provides a viable solution by supporting both low- and high-bandwidth requirements over a single infrastructure capable of upgrading wherever and whenever necessary. The patent-pending technology allows a low-cost shared ring to coexist with a DWDM ring, creating two rings on the same fiber. One ring is a single channel that is shared by all network elements and runs at 1310 nm. The second is a multichannel DWDM ring running at 1550 nm.

The SWDM enables all sites to communicate at a variety of speeds using the 1310-nm shared ring, while only sites requiring very high bandwidth tap into one or more of the 1550-nm DWDM wavelengths. Only the high-bandwidth sites pay for DWDM optics. As a customer's traffic grows on a particular site, it can be up graded, without service disruption, to access the 1550-nm channels. Event ually, if needed, the entire ring can support DWDM. Con versely, if demand never materializes, the carrier never incurs the expense of deploying DWDM.

"We're taking a positive stance on Chromatis's initial launch of its SWDM," says Chris Nicoll, director of infrastructure analysis at Current Analysis (Sterling, VA). "We like the capability to drop off bandwidth services at lower cost and complexity than is currently available via SONET or traditional DWDM solutions, without using DWDM at each location."

Nicoll believes that if Chromatis is successful in implementing its technology and getting service providers to install it, there is potential for metropolitan services to become available to a broader market than is currently available. One hitch, however, may be the sheer number of vendors also targeting the metropolitan market. Chromatis, founded in 1997, is butting heads with some industry giants, including Lucent Technologies, Nortel Networks, Cisco Systems, Alcatel, and others. The competition is staggering, not just in product, but in service, support, channels, financing, and reputation.

"We acknowledge the challenge, but highly integrated products like the ones being developed by Chromatis represent a challenge for traditional equipment providers as well," says Bob Barron, president and chief operations officer at Chromatis. "The technologies involved span multiple groups, often multiple divisions, who view products and markets in terms of distinct technologies. We see this type of integration as our core competence. It's a great market opportunity for the experienced cross-disciplinary team that Chromatis has put together."

Chromatis has developed systems that integrate SWDM with higher-level protocols such as time-division multiplexing, Asynchronous Transfer Mode, and Internet protocol and is currently testing these solutions in carrier networks. The company plans to release the SDWM-based product line in January.

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