Efficient transfer of bulk data requires routing that minimizes the net transfer time instead of providing flow level bandwidth guarantees. In this work, we consider a realistic scenario where available bandwidth for each link in a given network is time varying. In such a network and for a given file size, we provide an optimal algorithm that minimizes the total time required to transfer the file from source to destination. We further consider the problem where path shifting is allowed to increase the net throughput for bulk data transfer. For this problem, we provide a dynamic programming based optimal algorithm that minimizes the number of path shifts required to transfer the file in the specified time. Solution to the above problems addresses both the performance and scalability issues that arise in large bulk data transfer for long duration of time.

Faults in some sensor networks are likely to be localized. The conventional metric of fault-tolerance - connectivity of the network graph - fails to capture any notion of locality. This research introduces a new metric - region-based connectivity - that incorporates the notion of locality.

A large optical network may carry multiple traffic classes with different priorities and fault-tolerance requirement. Higher priority traffic may require having a back-up path so that the traffic can be switched quickly to this path in case of a failure in the primary path. The lower priority traffic classes may not have any such requirement. In the path protection schemes currently in use for the WDM networks, a backup path is computed for all traffic, whenever a primary path is established between a source-destination pair. The resource needed for communication using the backup path are reserved (or set aside) for data communication between a source-destination pair, and are utilized only when the primary path is unavailable due to a failure in the network. The traffic carrying capacity of a network can be increased, if the resources set aside for the backup paths are utilized for data communication. In this paper we propose a path protection scheme for networks with multiple classes of traffic. The key features of our scheme are (i) not all traffic classes have backup paths - only higher priority classes have backup paths, (ii) primary paths of lower priority share wavelengths with secondary paths of higher priority traffic, and (iii) lower priority traffic can be preempted by higher priority traffic in case of a failure. The sharing of a wavelength between a primary path of a lower priority communication with the secondary path of a higher priority communication allows the network to satisfy more call requests, thereby reducing the call blocking probability. We provide a mathematical programming formulation for computing the primary and backup paths for call requests in a dynamic environment. We also compute the call blocking probability of our scheme and compare it with the call blocking probability of the conventional scheme through simulation. Our experimental results show significant gain by the proposed scheme over the conventional scheme.

We consider the problem of routing the lightpaths of a logical topology of a WDM network on an arbitrary physical topology, such that the logical topology remains,connected even after the failure of a physical link. We focus our attention on the ring interconnection as the logical topology because it is widely used in many protection schemes. We first establish the necessary and sufficient condition for a ring logical topology to withstand failure of a single physical link. Next we show that the testing of this necessary and sufficient condition is an NP-complete problem. Finally, we give an algorithm for testing the necessary and sufficient condition and demonstrate the execution of the algorithm with the help of an example.

We consider the problem of routing the lightpaths of a logical topology of a WDM network on an arbitrary physical topology, such that the logical topology remains connected even after the failure of a physical link. In a previous paper Modiano et. al. (see Proc. IEEE INFOCOM'01, 2001) introduced the notion of survivable routing and established a necessary and sufficient condition for the existence survivable routes of a logical topology in a physical topology. In this paper we show that the problem of determining whether survivable routing is possible for a logical topology in a given physical topology is an NP-complete problem. Moreover we show that the problem remains NP-complete, even when the logical topology is restricted to be a ring with a specific ordering of the nodes.