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Today there are many challenges faced by the telecommunication industry. The storage and networking capacity is increasing rapidly and so is the traffic flowing over these networks. In comparison, the traffic rate is increasing much faster than the capacity provided in the networks. To overcome this problem, the concept of Internet protocol (IP) over dense wavelength division multiplexing (DWDM) has been introduced. It is the transfer of raw IP packets over an optical layer using DWDM for its capacity and operations. This new technical solution can increase the capacity of existing networks without the need for expensive re-cabling and can tremendously reduce the cost of network upgrades. It also supports the concept of all-optical network. However, as the system has a limited number of wavelengths available, re-usability of wavelengths is required. This causes one of the major problems of DWDM networks called the routing and wavelength assignment (RWA) problem. RWA is divided into two sub-problems: to find the best possible route for any given source-destination pair and to assign wavelengths to the route such that no two routes sharing a link are assigned the same wavelength. A number of algorithms exist for these sub-problems. For example, the shortest path and link state routing algorithms for routing and sequential algorithms for wavelength assignment. Another important issue related to DWDM networks is the wavelength continuity constraint that does not allow wavelength conversion during the transfer of data over a route. It is imposed because the wavelength converters are expensive hardware and introduce latency. This results in an increase in the blocking probability. However, providing conversion capability to a subset of nodes improves the performance considerably.
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