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Introduction To Dense Wave Division Multiplexing (DWDM)

 

            Topic: Introduction to Dense Wave Division Multiplexing (DWDM).
            
             This paper covers the how the need for Wave Division Multiplexing (WDM) and Dense WDM became essential and the basic difference between WDM and DWDM. Alternatives to DWDM are explored including Time Division Multiplexing (TDM) and Optical TDM (OTDM). An example of the difference between TDM and WDM is shown in a detailed example. The major components of a WDM system are explored. A few vendor products providing DWDM, the major features of each product, and the product capacities are compared. This paper concludes with some potential deficiencies of a DWDM system.
             Introduction.
             The Need For Fiber.
             The first generation optical networks, circa 1960, used single wavelength transmission and electrical-based switches for routing and processing. By using electrical switches, the optical signal must be converted to an equivalent electrical signal, processed by the electrical-based switches, and converted back to an optical signal. This significantly slowed down the otherwise optical network, as the transmission along a particular logical path is as fast as the slowest link. .
             If you think of a road between two points, imagine the road surface is made of different materials. At some points, the road is made of a material like concrete that allows high-speed travel similar to a highway, where the maximum safe speed is relatively high. Along other sections, the road is made of concrete marred with potholes or compacted dirt that allows for fast travel, but because of the road material, the maximum safe speed of the road is slower than a highway. Although the traveled speed along the highway is quick, the speed traveled along the dirt road is slower, thus slowing down the overall transmission by increasing delay. Similarly, early optical networks were "slowed down" by using electrical switches in the transmission path. This was not an issue in early optical networks because the amount of traffic along the fiber optic paths was small during the 1960's.


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