A dynamic reconfiguring tool for improving multiwavelength transport network robustness

In this paper we present a heuristic tool known as the virtual permanent reconfiguring mechanism (VPRM) which dynamically reconfigures wavelength connections in a WDM transport network with a given physical topology. VPRM seeks to provide an optimised semi-permanent solution of the network configuration or logical topology, and traffic flow of a WDM transport network. The tool is activated in the event of changes within network environment; these may include: (i) normal network environment changes such as a change in traffic pattern, network expansion (introduction of new nodes or increase in wavelength availability) and line shutdown for maintenance purposes and, (ii) abnormal network environment changes such as sudden power failure, and network faults. Detection of the former network changes is achieved using a threshold detection technique. The latter, changes however are detected by means of fault alarm signals from distributed fault restoration mechanisms. The VPRM employs a combination of integer linear programming (ILP) and a heuristic approach. It essentially balances the traffic utilisation throughout the network physical structure and it dynamically ensures that spare connections are available, even after a fault, prior to completion of network maintenance. Unlike other reconfiguration techniques which involve solving ILP problems, the VPRM not only balances the load distribution throughout the physical network but also reduces the overall mean traffic level within each link