PDF of this tutorialThe first fiber-optic communication system was installed by AT&T and GTE in 1977. Since then, optical fibers have steadily overtaken copper cables as the medium of choice for modern-day networks. The performance and reliability advantages are obvious. Fiber optics today are used almost exclusively in the physical layers of wide-area networks around the globe, and the development of metropolitan optical networks is already underway.
Today, one of the highest-growth optical-networking markets is carrier-delivered wavelength services for enterprise applications. To satisfy that demand, a new class of small, power-efficient, easy-to-install optical platforms designed specifically for enterprise deployment has emerged. This tutorial will examine the market forces and technological developments that spawned today’s reality.
Large financial institutions seeking high-bandwidth solutions for disaster recovery, as well as other business applications, began deploying private fiber-based networks between facilities in the early 1990s. At the time, local-exchange carriers (LECs) were pushing existing synchronous optical network (SONET) transport or asynchronous transfer mode (ATM) access services as the best and only transport technologies for metro enterprise networking.
Enterprises, however, soon discovered SONET and ATM to be ineffective options for the higher-speed data protocols that they more and more sought to adopt: enterprise system connectivity (ESCON), coupling link, fibre channel, and Gigabit Ethernet. WDM emerged for these enterprise applications shortly after systems were defined for the long-haul telecommunications market.
Multiplexing techniques were nothing new. Frequency division multiplexing (FDM), a standard technique in analog transmission systems such as cable television, assigns a separate frequency for each communications channel. Time division multiplexing (TDM), a standard technique in digital transmission systems, combines multiple low-speed channels in specific time slots of a higher-speed channel. WDM works on the same principles as FDM and TDM—only that the channel discriminator is neither frequency nor time but wavelength.
WDM multiplies the capacity of optical fiber strands, creating virtual channels and unlocking the full bandwidth potential of fiber (beyond 25,000 Gbps). Incoming application traffic is converted to specific wavelengths and multiplexed. Multiple channels are transmitted over the same fibers. There is no performance degradation or specific protocol requirements because light waves of different lengths do not interfere with one another during transmission and are converted back to their original formats at output. Today, dense WDM (DWDM) solutions utilizing 32 narrowly spaced channels are available through many of the leading equipment vendors.
So, in the mid 1990s, enterprises welcomed WDM as an excellent technique for improving bandwidth performance over private dark fiber. Across distances up to 50 kilometers, enterprises for the first time could transmit a multitude of disparate data protocols such as ATM, coupling link, ESCON, Ethernet, Fast Ethernet, fiber distributed data interface (FDDI), fibre channel, fiber connection (FICON), Gigabit Ethernet, SONET, symmetric remote data facility (SRDF), sysplex timer, and others simultaneously and at native speeds without impact on network performance.
Still, there were limitations. The lack of dark fiber available between facilities brought carriers into the mix. Some manufacturers of optical-networking platforms found themselves selling enterprise WDM systems to carrier customers driven to provide some solution for large enterprise networks. New platforms emerged, tailored specifically for service delivery and based on real feedback from large enterprise users and carriers. These platforms were engineered from the ground up to be integrated into carrier optical networks, relieving fiber congestion in the core network and enabling fast provisioning of end-to-end wavelength services.
Today, carriers are focusing on wavelength services to answer exploding demand from their enterprise customers for voice, data, and Internet application support across metropolitan areas. These services significantly expand the revenue opportunity for services while controlling the incredible bandwidth potential of their dark fiber.
