Module 20 : WDM Networks
Lecture      : WDM Networks
   
1.
 For a network not using wavelength converter, wavelength continuit condition requires that along any light path, the same
  wavelength must be used throughout. This is sometimes a restrictive condition because it does not allow establishment of a path between nodes even when a wavelength channel is available. Consider a case shown in the figure where two wavelengths $ \lambda_1$and $ \lambda_2$are available. There is one light path between N-1 and N-2 and a second light path between N-2 and N-3, the former using the wavelength $ \lambda_1$and the latter $ \lambda_2$.

\includegraphics{wdm23}

   
 

As only two wavelength are available, it is not possible to establish a light path between N-1 and N-3 (without violating continuity condition) though there is a free wavelength between each of the segments. However, if a wavelength converter is located at the node N-2, we may relax the continuity condition, as shown in the right hand figure.

The degree of wavelength conversion used in a given network depends on the traffic pattern in the network. The figure below illustrates different situations for a single input port and a single output port.

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