Selective bandwidth technology bridges SONET, DWDM

A new technology from Chromatis Networks Inc. (Bethesda, MD) that promises to make dense wavelength-division multiplexing (DWDM) affordable in bandwidth-varying metropolitan area networks (MANs) may also prove to be a solution for diverse campus communications.

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Steve Smith

A new technology from Chromatis Networks Inc. (Bethesda, MD) that promises to make dense wavelength-division multiplexing (DWDM) affordable in bandwidth-varying metropolitan area networks (MANs) may also prove to be a solution for diverse campus communications.

Selective wavelength-division multiplexing (SWDM) lets carriers deliver one or more DWDM wavelengths to data-intensive sites that require multigigabit capacities, while other less bandwidth-demanding sites can use traditional transmission technologies such as Synchronous Optical Network (SONET) on a less expensive optical ring. In essence, the patent-pending technology allows a low-cost shared ring to coexist on the same fiber as a DWDM ring.

Though SWDMs are initially targeted for MANs, the possibilities for their use in campus communications remain viable. "We certainly have had people interested in that possibility," says Doug Green, Chromatis`s vice president of marketing. In fact, he adds, "there`s been greater demand for beta version than the resources to support it." The technology is expected to be fully available in January.

To deliver higher bandwidth over even next-generation SONET systems, carriers must deal with added time and expense of adding more fiber and equipment to the MAN. "Conventional DWDM systems can scale more easily," says Chromatis president and chairman Rafi Gidron, "but they require every site on the ring to use high-cost optics. SWDM solves this dilemma by delivering multiwavelength optics where necessary on a site-by-site basis, while providing a seamless path for other sites to upgrade." With SWDM, carriers can upgrade sites to full DWDM without disrupting service to the site.

SWDM creates two rings on the same fiber. One is an inexpensive single-channel ring that is shared by all network elements and runs at 1310 nanometers. The other is a multichannel DWDM ring running at 1550 nm for sites that need very high bandwidth. The technology manages the two separate rings to make them appear as a single network. Carriers can upgrade any site at any time to access the 1550-nm DWDM ring, without disrupting service or affecting operation within the rest of the ring.

Although SWDM offers the promise of bandwidth flexibility within a MAN or campus setting, it will also require increased system "intelligence" to manage the diversity. In November, Chromatis began testing higher-level systems geared toward implementing SWDM--systems incorporating time-division multiplexing, Asynchronous Transfer Mode, and Internet protocol. These higher-level protocols are needed to permit multiple network elements to use the 1310-nm shared channel simultaneously, format raw capacity into a form that can be used by attached network equipment without service overlay, and permit connectivity and restoration to support multi-ring, hub, and ring/mesh combinations.

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Chromatis Networks` selective SWDM creates two rings on the same fiber--an inexpensive single-channel ring running at 1310 nm and shared by all network elements and a multi-channel DWDM ring running at 1550 nm for sites that need very high bandwidth.

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