Blinded by the wave-division light

If you haven't heard of wave-division multiplexing (WDM), you probably will in the coming months. WDM and a closely related technology, dense wave-division multiplexing (DWDM), are giving large users, telecommunications carriers and competitive service providers the opportunity to quickly increase bandwidth capacity and speeds.

Under consideration
WDM is useful for large companies whenever high-speed interconnection is needed between widely dispersed sites. The technology is also important for corporations that maintain multiple data centers, either for distributed applications, disaster recovery or CPU redundancy.

In addition, nearly every major telecommunications carrier is considering WDM technology. Almost all competitive providers are thinking about building their networks based on WDM, whether across the country or within a metropolitan area. The connectivity offered by WDM will bring the LAN, WAN and telecommunications infrastructure closer without requiring new cable installations.

According to researchers, current fiber technologies use less than 1% of fiber cable capacity because the technologies transmit using one wavelength per fiber link. Moreover, the most common method of forwarding traffic over fiber, time-division multiplexing, can't simultaneously handle multiple bit rates, framing types or protocols.

In addition, the Internet has placed a heavy burden on global networks to handle a very different kind of telecommunications traffic. Video services are emerging in which applications swallow bandwidth like finger food, and the use of telephone communications is growing exponentially and globally. For carriers and end users, the issue of increasing capacity to reflect demand can be a multibillion-dollar decision.

When conduit becomes full and the fiber within has been completely used, choices for increasing capacity dwindle. One choice is to dig up roads and lay more conduit and fiber. But WDM and DWDM offer a more appealing answer to the problem of capacity by enabling carriers and users to employ the same fiber with far more capacity.

WDM and DWDM devices get around these limitations by transmitting multiple signals through the same fiber cable. Much like a prism, WDM uses multiple wavelengths, or colors of light, fired down a single fiber to multiply fiber capacity.

WDM switches use lasers to divide incoming data - be it from a voice, video or data device - into separate optical wavelengths, or lightstreams, across a fiber link between two switches. A lightstream basically becomes a high-bandwidth pipe capable of carrying data at gigabit speeds. Each link can carry several wavelengths, using optical WDM. The lightstreams are then mixed together and travel over a single fiber cable to another WDM switch, which demultiplexes the traffic.

The difference between WDM and DWDM is that DWDM lets a lightstream carry multiple types of data on a single fiber. For example, rather than having separate ATM, LAN and video lightstreams, users can get the ATM, LAN and video on a single strand.

WDM and DWDM let users or service providers set priorities, as well. If ATM traffic needs to arrive before IP, switches can be configured as such.

Some WDM products, such as IBM's Muxmaster, let users link remote locations up to 31 miles apart. And some companies, such as Ericsson, have been working with DWDM to combine lightstreams into a single wavelength, boosting by up to four times the capacity of a single lightstream.

In addition, backbone stalwart Cisco Systems, Inc. recently said it would begin offering switches and routers that deploy WDM and DWDM interfaces. Cisco is teaming with Ciena Corp. to deliver optical internetworks based on Cisco's high-end switching and routing platforms and Ciena's DWDM equipment.

WDM is an equal-opportunity system for users or carriers that need to share infrastructure between several technologies. For example, WDM supports high-speed connectivity to ATM, and bridges the LAN, WAN and telecommunications networks.

WDM and DWDM are two of the fastest ways to build an infrastructure capable of proving new bandwidth with minimum delay. Installing new capacity - if you have a WDM backbone - is faster than installing new fibers and new client technology from scratch.

Daza is vice president of business development in the Transport and Cable Networks business unit of Ericsson Telecom. Genin is vice president of optical networking solutions for Ericsson U.S.

Blinded by the wave-division light

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