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americasnetwork.com
It's metro time for DWDM
Local exchange carriers that have been waiting to test drive metro DWDM can start their engines.
By Annie Lindstrom
Dense wavelength division multiplexing (DWDM) has made a home in the nation's long-haul fiber optic networks. There's no question it's needed there, as it would cost millions to lay new fiber to meet increased demand. But what about the metro area? Will there soon be enough data traffic waiting at the edge of the network to make it more economical to use DWDM in the metro area for data networking purposes?
In 1999, competitive and incumbent local exchange carriers (CLECs and ILECs) will begin kicking the tires of ring-based metro DWDM systems. The new systems will offer optical layer protection switching, which will make them particularly suited for the optical transport of higher-than-synchronous optical network (Sonet) speed data across and within the local metropolitan area. Carriers that have been wanting to build local networks minus expensive Sonet gear now can do so.
Now is a good time to try to understand the differences between long-haul DWDM systems and metro DWDM systems. Although both increase the capacity of an installed fiber by adding additional channels to it, about the only other thing they seem to have in common are the letters D-W-D-M.
Going the distance
A long-haul DWDM system's main purpose in life is to transport as much traffic as possible from one point to another over long distances of approximately 300 km to 1,000 km. Traffic is generally multiplexed onto long-haul systems via a Sonet multiplexer (mux) and carried their length at either OC-48 (2.5 Gbps) or OC-192 (10 Gbps) Sonet rates. Because their goal is to perform reliably and under control, the components used in the amplifiers and terminals are precisely engineered and therefore very expensive.
The I/O application meets a real need, but equipment suppliers and service providers have much more in mind for metro DWDM. Both say it won't be long before CLECs and ILECs and even Internet service providers (ISPs) are using metro DWDM systems in mesh and/or ring configurations to transport high-bandwidth data traffic from business to business within a metro area. The new systems will save carriers and customers time and money when they just don't have enough of either to engineer and deploy new Sonet networks to handle unforecast traffic growth. However, even if they could build them fast enough and cheaply enough, due to their bandwidth limitations, Sonet networks will not be able to carry new types of data traffic, such as gigabit Ethernet, Enterprise Systems Connection (ESCON), or D1 video at native speeds, whereas metro DWDM systems will.
The price is right
Because they don't have to transport traffic very far, metro DWDM systems can be manufactured at a cost compatible with or below that of laying another fiber.
"Because the distances are short and distortion isn't as great, the systems don't need amplification or high-performance modulators, so the expense of the system isn't as great," says Steve Chaddick, senior vice president of strategy and corporate development at Ciena (Linthicum, Md.).
Most metro DWDM systems will be deployed in mesh, ring or star topologies which allow traffic to be added or dropped at multiple points within the metro area. However, optical add/drop functionality will be limited in initial products, most of which will not support dynamic wavelength routing.
"Metro systems will be more advanced and provide us with a ring for drop and insert. That would be more desirable, but in some cases people are not looking for that much redundancy" Hensley says. "There are many applications where a single thread is what they've called for and want to pay for, so we accommodate that using the FireFly."
GST is using the metro system to reclaim multiple fibers that it otherwise would have had to run to each customer in the buildings it serves. On a 10-building block, for example, the carrier deploys a FireFly terminal in each building and runs one fiber to each building and puts the traffic of every customer in that building onto its own wavelength on that fiber. When metro products with add/drop functionality are available, GST will be able to run a single fiber down the street and pick up traffic from each building on that same fiber by putting a DWDM ADM box in front of each building, Hensley explains.
"Our primary mode of serving customers is ATM to the customer. That allows us to take one color and use it to serve several buildings, gaining more and more efficiencies," adds Kevin Wright, GST's chief technology officer. "By placing an ATM switch in the basement, I can operate it and hook up video, voice and IP service for multiple customers. I'm able to turn up their services faster and I can see into the box in their building. That cuts the cost of provisioning way down and improves the quality of service."
Hiram
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