Design of Logical Topologies

As we addressed in the previous chapter, in single-hop systems of WDM networks a connection is set up by selecting a path of physical links and assigning a (reserved) wavelength to these links. Because of limitations on the number of available wavelengths on the fibers, and hardware constraints at the nodes, it is impossible to set up a lightpath for each of connections between every pair of source-destination nodes. The set of lightpaths that are set up on the physical topology constitutes a logical (also called virtual) topology. One of the major advantages of WDM networks is that it is able to reconfigure its logical topology to adapt to changes of traffic patterns and network conditions.