Routing dependable connections with specified failure restoration guarantees in WDM networks

This paper considers the problem of dynamically establishing dependable connections (D-connections) with specified failure restoration guarantees in wavelength-routed wavelength division multiplexed (WDM) networks. We call a connection with fault-tolerant requirements a D-connection. We recommend using a proactive approach to fault-tolerance wherein a D-connection is identified with the establishment of a primary and a backup lightpath at the time of honoring the connection request. However, the backup lightpath may not be available to a connection throughout its existence. Upon occurrence of a fault, a failed connection is likely to find its backup path available with a certain specified guarantee. We develop algorithms to select routes and wavelengths to establish D-connections with specified failure restoration guarantees. The algorithms are based on a technique called primary-backup multiplexing. We present an efficient and computationally simple method to estimate the average number of connections per link for which the backup paths are not readily available upon occurrence of a link failure. This measure is used for selecting suitable primary and backup lightpaths for a connection. We conduct extensive simulation experiments to evaluate the effectiveness of the proposed algorithms on different networks. The results show that the blocking performance gain is attractive enough to allow some reduction in guarantee. In particular, under the light load conditions, more than 90% performance gain is achieved at the expense of less than 10% guarantee reduction