Suresh Chalasani

Fault-tolerant wormhole routing algorithms for mesh networks

We present simple methods to enhance the current minimal wormhole routing algorithms developed for high radix, low dimensional mesh networks for fault tolerant routing. We consider arbitrarily located faulty blocks and assume only local knowledge of faults. Messages are routed minimally when not blocked by faults and this constraint is relaxed to route around faults. The key concept we use is a fault ring consisting of fault free nodes and links can be formed around each fault region. Our fault tolerant techniques use these fault rings to route messages around fault regions. We show that, using just one extra virtual channel per physical channel, the well known e cube algorithm can be used to provide deadlock free routing in networks with nonoverlapping fault rings; there is no restriction on the number of faults. For the more complex faults with overlapping fault rings, four virtual channels are used. We also prove that at most four additional virtual channels are sufficient to make fully adaptive algorithms tolerant to multiple faulty blocks in n dimensional meshes. All these algorithms are deadlock and livelock free. Further, we present simulation results for the e cube and a fully adaptive algorithm fortified with our fault tolerant routing techniques and show that good performance may be obtained with as many as 10% links faulty. >

Resource deadlocks and performance of wormhole multicast routing algorithms

We show that deadlocks due to dependencies on consumption channels are a fundamental problem in wormhole multicast routing. This type of resource deadlocks has not been addressed in many previously proposed wormhole multicast algorithms. We also show that deadlocks on consumption channels can be avoided by using multiple classes of consumption channels and restricting the use of consumption channels by multicast messages. We provide upper bounds for the number of consumption channels required to avoid deadlocks. In addition, we present a new multicast routing algorithm, column-path, which is based on the well-known dimension-order routing used in many multicomputers and multiprocessors. Therefore, this algorithm could be implemented in existing multicomputers with simple changes to the hardware. Using simulations, we compare the performance of the proposed column-path algorithm with the previously proposed Hamiltonian-path-based multipath and an e-cube-based multicast routing algorithms. Our results show that for multicast traffic, the column-path routing offers higher throughputs, while the multipath algorithm offers lower message latencies. Another result of our study is that the commonly implemented simplistic scheme of sending one copy of a multicast message to each of its destinations exhibits good performance provided the number of destinations is small.

A framework for designing deadlock-free wormhole routing algorithms

This paper presents a framework to design fully-adaptive, deadlock-free wormhole algorithms for a variety of network topologies. The main theoretical contributions are: (a) design of new wormhole algorithms using store-and-forward algorithms, (b) a sufficient condition for deadlock free routing by the wormhole algorithms so designed, and (c) a sufficient condition for deadlock free routing by these wormhole algorithms with centralized flit buffers shared among multiple channels. To illustrate the theory, several wormhole algorithms based on store-and-forward hop schemes are designed. The hop-based wormhole algorithms can be applied to a variety of networks including torus, mesh, de Brujin, and a class of Cayley networks, with the best known bounds on virtual channels for minimal routing on the last two classes of networks. An analysis of the resource requirements and performances of a proposed algorithm, called negative-hop algorithm, with some of the previously proposed algorithms for torus and mesh networks is presented.

Fault-tolerant wormhole routing in tori

We present a method to enhance wormhole routing algorithms for deadlock-free fault-tolerant routing in tori. We consider arbitrarily-located faulty blocks and assume only local knowledge of faults. Messages are routed via shortest paths when there are no faults, and this constraint is only slightly relaxed to facilitate routing in the presence of faults. The key concept we use is that, for each fault region, a fault ring consisting of fault free nodes and physical channels can be formed around it. These fault rings can be used to route messages around fault regions. We prove that at most four additional virtual channels are sufficient to make any fully-adaptive algorithm tolerant to multiple faulty blocks in torus networks. As an example of this technique, we present simulation results for a fully-adaptive algorithm and show that good performance can be obtained with as many as 10% links faulty.

Data Architectures for RFID Transactions

We focus on the data models for storing the data generated by radio frequency identification (RFID) transactions and architectures for processing such data. We consider the supply chain comprised of the manufacturer, distributor, retailer, and the consumer. We discuss details of the data generated by RFID transactions and data models to store such data. Different organizations in the supply chain may use this data for different applications such as automatic product ordering, shelf replenishment, and product recall. We present models to anticipate the data requirements generated by RFID transactions and indicate how existing enterprise applications can be adapted to handle RFID data. The results presented in this paper will help a practitioner to 1) design and develop databases and applications for handling RFID data and 2) significantly reduce the storage requirements of RFID data. Using the data architectures, we discuss two supply chain applications-product recall and shelf replenishment-in detail. We present analytical models for the cost and time required for shelf replenishment in a retail store.

On multicast wormhole routing in multicomputer networks

We show that deadlocks due to dependencies on consumption channels is a fundamental problem in multicast wormhole routing. This issue of deadlocks has not been addressed in many previously proposed multicast algorithms. We also show that deadlocks on consumption channels can be avoided by using multiple classes of consumption channels and restricting the use of consumption channels by multicast messages. In addition, we present a new multicast routing algorithm, column-path, which uses the well-known e-cube algorithm for multicast routing. Therefore, this algorithm could be implemented in the existing multicomputers with minimal hardware support. We present a simulation study of the performance of Hamilton-path based multicast algorithms with the proposed column-path algorithm. Our simulations indicate that the simplistic scheme of sending one copy of a multicast message to each of its destinations exhibits good performance and that the new column-path algorithm offers higher throughput compared to the Hamilton-path based algorithms.<<ETX>>

Resource placement with multiple adjacency constraints in k-ary n-cubes

The problem of placing resources in a k-ary n-cube (k>2) is considered in this paper. For a given j/spl ges/1, resources are placed such that each nonresource node is adjacent to j resource nodes. We first prove that perfect j-adjacency placements are impossible in k-ary n-cubes if n >

Models for Cost-Benefit Analysis of RFID Implementations in Retail Stores

We present models for cost-benefit analyses of RFID implementations for retail stores. We discuss implementations of the data networks connecting the tag readers. Our models consider the cost of implementations including the cost of tag readers, the communication network cost and other infrastructure cost. In addition, we also present analytical models to consider the benefits of these implementations including automatic check-out and reduced inventory costs due to efficient shelf replenishment

Fault-tolerant routing with non-adaptive wormhole algorithms in mesh networks

We present simple techniques to enhance the e-cube algorithm for fault-tolerant routing in mesh networks. These techniques are based on the concept of fault rings, which are formed using fault free nodes and links around each fault region. We use fault rings to enhance the e-cube to route messages in the presence of rectangular block faults. We show that if fault rings do not overlap with one another-the sets of links in fault rings are pairwise disjoint, then two virtual channels per physical channel are sufficient to make the e-cube tolerant to any number of faulty blocks. For more complex cases such as overlapping fault rings and faults on network boundaries, three or four virtual channels are used. In all cases, the routing guarantees livelock and deadlock free delivery of each and every message injected into the network. Our simulation results for isolated faults indicate that the proposed method provides acceptable performance with as many as 10 percent faulty links.<<ETX>>

A support system for mediating brownfields redevelopment negotiations

Purpose – To present a support system which will be useful to mediators of brownfield redevelopment negotiations between government and industry representatives.Design/methodology/approach – The support system optimizes a weighted utility function of the parties involved in the negotiation. It provides not only the optimal solution but also some sensitivity reports which the mediator can use to lead the negotiations in the most effective direction.Findings – The spreadsheet technology is sufficient to solve the optimization problem and produce sensitivity reports in real time. Consequently, a mediator equipped with a laptop computer can lead the negotiations efficiently.Research limitations/implications – It is possible to achieve Pareto optimal contingent contracts among the stakeholders of brownfield redevelopment projects.Practical implications – Many negotiations that were stalled in the past could be completed successfully using the support system presented here. New negotiations might be completed m...