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Strike Up the Band

April 1, 2006
by Leo Bodden
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Our bandwidth costs were already on a steady climb: 20 percent annual growth for five years running. And we hadn't even yet implemented PACS — the break-through, but bandwidth-intensive, picture archiving and communication system application. We needed an intelligent solution.

The implementation of dense wavelength division multiplexing (DWDM) technology has halted New York-Presbyterian Hospital's escalation in costs and effectively future-proofed our network for foreseeable growth in bandwidth demand. Long-term cost avoidance was the primary driver behind our decision. By making the decision now to upgrade to DWDM, we have effectively leveled future bandwidth costs at what they are today — while providing the bandwidth we need for PACS and an array of life-saving services.

Consistently ranked as one of the top hospitals in the country in U.S. News & World Report's guide to "America's Best Hospitals," New York-Presbyterian is the nation's largest not-for-profit, non-sectarian hospital. We provide state-of-the-art inpatient, ambulatory and preventive care in all areas of medicine through five major centers. Today, the New York-Presbyterian Healthcare System — an affiliation of acute-care and community hospitals, long-term care facilities, ambulatory sites and specialty institutes — has grown to serve one in four patients in the New York metropolitan area.

Arriving at DWDM

The first solution we considered was simply expanding our existing asynchronous transfer mode infrastructure with additional synchronous optical network (SONET) rings or point-to-point DS-3 land-line connections. Quickly, however, it became clear that this was neither a simple nor long-term solution. Deploying Ethernet-based applications over a SONET infrastructure would require complex spanning tree configurations for redundancy, and, in fact, the links would have been saturated with traffic even before our new applications were implemented.

WDM-enabled optical networking offered a compelling alternative. With WDM, individual applications are assigned wavelengths of light, multiplexed at one end of a strand of an optical-fiber link and de-mulitplexed at the other. Because the light wavelengths do not interfere with one another, traffic from multiple protocols can be carried over the same strand of optical fiber — and application performance is native speed. Protocol conversion is unnecessary, so there are no limitations regarding bit rates or latency.

Dense WDM (DWDM), coarse WDM (CWDM) and even hybrid CWDM/DWDM platforms are available. The difference between DWDM and CWDM is how densely wavelengths are arranged. CWDM uses 20-nanometer spacings, enabling up to eight "virtual channels" for application traffic to be created on a single strand of optical fiber. In DWDM, wavelengths are more tightly arranged — spaced 1.6 nanometers or less between one another. This enables up to 64 virtual channels of application traffic to be created on a strand.

DWDM platforms require higher cost components, so they tend to be more expensive than CWDM models. Yet we chose the unsurpassed scalability of DWDM because it offered an opportunity to create a network infrastructure that we are confident will serve us for the next five to 10 years.

With this solution in place, we'll be running at only 10 percent of the bandwidth capacity of our infrastructure, even with PACS fully implemented. With all foreseeable bandwidth demand in place, we'll still be running at only 20 percent capacity. We have developed a cost-effectively scalable infrastructure that we believe will accommodate our bandwidth growth for at least the next 10 years.

Fast, flexible and resilient

New York-Presbyterian Hospital deployed ADVA Optical Networking's Fiber Service Platform (FSP) 3000 DWDM systems at all five of our Manhattan campus locations, including data centers and patient-care facilities. The network, enhanced with erbium doped fiber amplifier (EDFA) modules that enable native-speed application performance over longer distances, is a ring and logical mesh architecture that measures 50 kilometers in circumference. We have realized a series of valuable benefits.

First, it's a high-speed, resilient infrastructure with zero single points of failure. One of the primary reasons we selected the ADVA system from the range of DWDM solutions that we considered was because, even if we lose power to a given location, pass-through traffic does not terminate on the impacted ADVA gear. Given our ring topology — and the fact that two of our sites have no capability for battery-power backup — this was a characteristic we felt we could not live without. The necessity of this feature was reinforced when New York and dozens of other cities in the eastern United States and Canada experienced an extended blackout in August 2003.

Second, the network provides simultaneous support for 64 channels of data, voice and video services of up to 10Gbit/s. The ADVA solution provides quality of service (QoS) capabilities that our mission-critical traffic is provided with dedicated bandwidth and controlled levels of jitter and latency.