One of the most promising solutions to deal with huge data traffic demands in
large communication networks is given by flexible optical networking, in particular
the flexible grid (flexgrid) technology specified in the ITU-T standard
G.694.1. In this specification, the frequency spectrum of an optical fiber link is
divided into narrow frequency slots. Any sequence of consecutive slots can be
used as a simple channel, and such a channel can be switched in the network
nodes to create a lightpath. In this kind of networks, the problem of establishing
lightpaths for a set of end-to-end demands that compete for spectrum resources
is called the routing and spectrum allocation problem (RSA). Due to its relevance,
RSA has been intensively studied in the last years. It has been shown
to be NP-hard and different solution approaches have been proposed for this
problem. In this paper we present several families of valid inequalities, valid
equations, and optimality cuts for a natural integer programming formulation
of RSA and, based on these results, we develop a branch-and-cut algorithm for
this problem. Our computational experiments suggest that such an approach is
effective at tackling this problem
