Contemporary technologies are coming to their limits in bandwidth provisioning. Therefore, evolution trends in transport networks use more intensive new technologies deployment. These new technologies concern mainly optical networks latest research: WDM circuit switching networks and optical packet networks.
Few decades ago, metallic cables were used for long distance data transport. They were replaced by optical fibers characterized by better quality parameters (error ratio, attenuation and higher bandwidth). Results of the research allowed even more efficient bandwidth use thanks to WDM multiplex.
WDM means that several wavelengths can be transported in parallel via one optical fiber. It is similar to frequency multiplex in classical networks. WDM is based on parallel transport of data on different wavelengths using one fiber. Therefore, wavelength can be used as supplementary information concerning packet routing. Data can be transported using one wavelength between end-points, but it is possible to use wavelength conversion in the nodes. Level of wavelength conversion in the nodes expresses also level of flexibility of WDM networks. It is possible to have WDM network without possibility of wavelength conversion, partial conversion and full conversion (Figure above). Event more, conversion can be implemented only in some nodes. Such approach leads us to serious problem, which is known as RWA (Route Wavelength Assignment). This problem is formulated how to optimize wavelength use between points in the network, which topology is known to maximize transported data and minimize PLR. Well-resolved RWA problem can also help with network topology design by minimizing degree of conversion. Let us stress that with increasing level of conversion in the network also management complexity and price increases. WDM is relatively new technology, but researchers are already preparing next step, which is optical packet switching network. In this case, we are talking about all-optical network, where data are transported via proposed network without being converted into electrical form.