ABSTRACT
Routing and spectrum allocation (RSA) in elastic optical networks (EONs) is considered one of the key functionalities due to its information transparency and spectrum reuse characteristics. RSA is used to find the appropriate route for a source and destination pair, and allocate suitable spectrum slots to the requested lightpath. This chapter reviews and classifies RSA approaches, including their pros and cons. The RSA problem in EONs is equivalent to the routing and wavelength assignment problem in wavelength-division multiplexing-based optical networks. The chapter focuses on different routing policies, namely— fixed routing, fixed alternate routing, least congested routing, and adaptive routing, with no consideration given to the elastic characteristics of optical networks. In EONs, single path routing via the RSA approach can create the spectrum fragmentation problem and thus inefficiency. The spectrum slot allocation of an individual connection request can be performed using one of the following allocation policies.
