Absrrucf-We consider the problem of constructing logical topologies over a wavelength routed optical network with no wavelength changers. In [2] the wavelength continuity constraints were formulated as a set of non-linear constraints and the objective considered was either delay minimization or minimizing the maximum offered load. Simulated annealing has been used to solve the non-linear optimization problem of [2]. In [3] the wavelength continuity constraint was relaxed, the nodes were equipped with wavelength changers, and the objective was to minimize the average hop length. This resulted in the hop lengths being small and hence reduced the number of wavelength changers being used, but the resulting logical topology did not reflect the traffic intensities between the nodes. In this paper we present a exuct lineur,fi)rmulution (mixed integer linear program) for designing a logical topology with no wavelength changers. Since the objective of our linear formulation is minimizing the maximum offered load on any link, which is called congesfion, the resulting logical topology reflects the traffic intensities between the nodes. Our linear formulation yields a logical topology and routing and wavelength assignment for the logical links. In [l] the problem of logical topology design is considered but the number of wavelengths the fiber can support is not a constraint. In this paper we take into consideration the number of wavelengths the fiber supports, the hop length of a logical link, and show the trade-offs involved in minimizing congestion. Since the whole problem is lidearizable the solution obtained by relaxation of the integer constraints yields a lower bound on the congestion. This can be used to compare the efficiency of heuristic algorithms. We solve the problem exactly for a small size network and for large size networks we devefop some heuristic algorithms to obtain a feasible solution using the solution obtained by relaxing the integer constraints. Following [6] we introduce a cutting plane which enables us to reduce the previously obtained upper bounds on congestion. Numerical results for a six node wide area network and the National Science Foundation Network (NSFNET) are presented for various cases.
Wavelength continuity constraint for the virtual topology design problem has been considered REF , i.e. it is assumed that nodes are not equipped with wavelength converters.
Design of logical topologies: A linear formulation for wavelength routed optical networks with no wavelength changers
Proceedings. IEEE INFOCOM '98, the Conference on Computer Communications. Seventeenth Annual Joint Conference of the IEEE Computer and Communications Societies. Gateway to the 21st Century (Cat. No.98
Proceedings. IEEE INFOCOM '98, the Conference on Computer Communications. Seventeenth Annual Joint Conference of the IEEE Computer and Communications Societies. Gateway to the 21st Century (Cat. No.98
Computer Science