Industry/University Collaboration at the University of Michigan-Dearborn: A Focus on Relevant Technology

https://deepblue.lib.umich.edu/bitstream/2027.42/154106/1/kampfner1998.pd

Performance enhancement of bus-based parallel/distributed systems

In a tightly coupled environment reusing slots in the traditional sense is not a lucrative option because each erasure node will introduce a few bits delay. For an on board system, where each slot is only a few bits long, such delay is intolerable. We have developed a method for reusing part of the bandwidth available from spatial/spectral bandwidth extension without introducing any buffering delay. Further, we have provided a polynomial time algorithm to optimally reconfigure the bus under the design constraints for any given traffic pattern. We have found that the reconfigured bus substantially outperforms the traditional slotted bus in most practical scenarios. In a dual-bus local area network the need for erasure nodes introduces a few bits of delay for each added erasure node, thus it is not profitable to make all nodes erasure nodes. This fact gives rise to the problem of placing a minimum number of erasure nodes on the network so that the throughput gain is maximum. This thesis gives the first polynomial time algorithm to solve the problem for all traffic conditions. The second part of the thesis considers partitioning and mapping task graphs for distributed shared memory systems (which includes bus based systems). The problem in its general form is known to be NP-complete and it is important to come up with simple but effective and fast heuristics. We have considered the tree task graphs which arise from many important programming techniques such as divide-and-conquer, branch-and-bound, etc. Further, we have proposed a polynomial time algorithm for data allocation in cacheless bus-based multiprocessor systems

EFFICIENT TASK PARTITIONING ALGORITHMS FOR DISTRIBUTED SHARED MEMORY SYSTEMS

In this paper, we consider the tree task graphs which arise from many important programming paradigms such as divide and conquer, branch and bound etc., and the linear task-graphs that stem from common computation schemes such as pipelining, iterative calculation etc.. The target architecture considered is a distributed shared memory architecture with indirect network or wormhole-routed direct network as its interconnection network (IN). The partitioning problem is formulated for systems where all or most of the communications are interleaved with task executions, in light of latency-hiding techniques employed in most of today’s multiprocessors. This is in contrast with previous research in this area where computation and communication are assumed to be completely non-overlapped. We propose a general method for solving the partitioning problem. This method involves three parameters, viz., bandwidth requirement, bottleneck, and load balancing factor that are used to judge the effectiveness of the partitioning and thus make the partitioning problem somewhat independent of mapping problem. Optimal sequential and parallel algorithms for partitioning tree task graphs such that the bottleneck is minimized with minimum number of processors are developed. It is shown that the bandwidth-requirement minimization problem is NP-complete for trees. However, the bandwidth-requirement minimization problem is known to be polynomial for linear task graphs, which are a special case of tree task graphs. An improved algorithm for obtaining the bandwidth-requirement minimizing partition of linear task graphs is presented. Furthermore, three effective, simple 2pass heuristics for computing bandwidth-requirement minimizing partition of tree task graphs are also presented. Parallel versions of the heuristics are developed as well. The effectiveness and efficiency of those heuristics are validated through extensive simulations. Key words. Distributed shared memory multiprocessors, Task graph partitioning, Bandwidth and bottleneck minimization, Load balancing. 1

A compiler-directed approach to network latency reduction for distributed shared memory multiprocessors

In distributed shared memory multiprocessor systems, parallel tasks communicate through sharing memory data. As the system size increases, such communication cost becomes the main factor that limits the overall parallelism and performance. In this paper, we propose a new solution to the problem through judiciously managing the relevant resource, namely, the shared data and the interconnection network (IN) through which the sharing is carried out. In this approach, communication cost is minimized by means of data migration/allocation which is based on analyzing general layered task graphs, sharing behavior of parallel tasks, and network topology. Our method is not applicable for read only variables. Further, for the time being, the usefulness of the method is limited to multiprocessors where no cache coherence mechanism is implemented. Four typical interconnection topologies for multiprocessors are considered, namely, shared-bus, hierarchical-bus, 2-D mesh, and fat-tree structures. Efficient data allocation algorithms for each of the four network topologies are developed that make decision on data allocation/migration at the compile time. The complexity of one algorithm is O(np) for shared-bus and O(n2p) for the remaining three in a system with n processors executing a p-layer task graph for one shared variable. We have also given an algorithm to determine optimal allocation/migration scheme for multiple shared variables. However, the cost of the algorithm become prohibitive when the number of shared variables is high. Therefore, a heuristic of low complexity is suggested. The heuristic is optimal for some topologies. © 1990 Academic Press, Inc

Recent advances in mobility modeling for mobile ad hoc network research

In this paper, we survey recent advances in mobility modeling for mobile ad hoc network research. The advances include some new mobility models and analysis of older mobility models. First we classify mobility models into three categories according to the degree of randomness. We introduce newly proposed mobility models in each of these categories. Next we discuss analysis for existing mobility models. We describe the analysis work in three parts. The first part is the statistical properties of the most widely used Random Waypoint Model. The second part describes the mobility metrics that aim to capture the characteristics of different mobility patterns. The last part is the impact of mobility models on the performance of protocols. We also describe some possible future work

A Distributed Authorization Server (DAS) Architecture for Sensor Networks

Abstract: Sensor networks are resource constrained environments. Further, sensor networks are not physically secured, i.e., sensor nodes may be physically captured and reverse engineered by the attacker. The goal of our research is to design energy-efficient Distributed Authorization Servers (DAS) resilient to logical attack (hacking) and physical attack. We propose to organize our DAS as a layered directed acyclic graph (DAG). Any request to a sensor must be routed through and authorized by every layer of the DAG. Similar concepts have been investigated by other researchers. Our research adds a structural component to the existing research. A common method for achieving longer life for a sensor network is to deploy redundant nodes and activate only a subset of nodes at one point of time. To the best of our knowledge, nobody addressed the problem of choosing the nodes to be activated. In this paper we designed a set of algorithms to choose the set of nodes for forming the DAS between the command and control centers (CCCs) and sensors collecting data. Our algorithms maximize the time required to compromise the security as well reduces the energy requirement for authorization and communication. I

An Optical Switching Architecture for Hierarchical Group Communication

We show that the problem of finding the maximum passable subset of a permutation through a banyan is NP-complete. We then describe a two-level optical interconnection structure for groups or clusters of end-nodes (LANs or processors). At the higher level, an optical banyan is used to switch wavelength multiplexed packets from the groups. Technologically di#cult switching of individual wavelengths is avoided by prearranging transmissions from the groups in a way that they can be switched in a wavelength insensitive manner. Further, by keeping the banyan conflict free, we allow each of the groups to access the entire set of wavelengths for multiplexing, thus maximizing the bisection bandwidth. The proposed optical interconnect can support multiple multicast connections between each pair of groups, in which source nodes may simultaneously multicast several di#erent packets to di#erent subsets within a destination group. System-wide multicasts and broadcasts can be achieved through repetitive group-to-group transmissions. The network uses readily available components such as opto-electronic directional couplers, fixed wavelength transmitters, and di#raction-based parallel receivers while avoiding the use of relatively slow and expensive tunable components

Categories and Subject Descriptors

In this paper, we survey recent advances in mobility modeling for mobile ad hoc network research. The advances include some new mobility models and analysis of older mobility models. First we classify mobility models into three categories according to the degree of randomness. We introduce newly proposed mobility models in each of these categories. Next we discuss analysis for existing mobility models. We describe the analysis work in three parts. The first part is the statistical properties of the most widely used Random Waypoint Model. The second part describes the mobility metrics that aim to capture the characteristics of different mobility patterns. The last part is the impact of mobility models on the performance of protocols. We also describe some possible future work

Quercetin Interferes With iron Metabolism in Leishmania donovani and Targets Ribonucleotide Reductase to Exert Leishmanicidal Activity

The possibility of developing antileishmanial drugs was evaluated by intervention in the parasite’s iron metabolism, utilizing quercetin (Qr) under in vivo conditions, and identifying the target of this lipophilic metal chelator against Leishmania donovani. Methods: Interaction between Qr and serum albumin (SA) was studied by using the intrinsic fluorescence of Qr as a probe. The effect of treatment with Qr and SA on the proliferation of amastigotes was determined by evaluating splenic parasite load. Disintegration of parasites in response to combination treatment was assessed from ultrastructural analysis using a transmission electron microscope. Quenching of the tyrosyl radical of ribonucleotide reductase (RR) in treated amastigotes was detected by an electron paramagnetic resonance study. Results: Treatment with a combination of Qr and SA increased bioavailability of the flavonoid and proved to be of major advantage in promoting the effectiveness of Qr towards the repression of splenic parasite load from 75%, P < 0.01 to 95%, P < 0.002. Qr-mediated down-regulation of RR (P < 0.05), catalysing the rate-limiting step of DNA synthesis in the pathogens, could be related to the deprivation of the enzyme of iron which in turn destabilized the critical tyrosyl radical required for its catalysing activity. Conclusions: Results have implications for improved leishmanicidal action of Qr in combination with SA targeting RR and suggest future drug design based on interference with the parasite’s iron metabolism under in vivo conditions