1327847
On achieving maximum multicast throughput in undirected networks
The transmission of information within a data network is constrained by the network topology and link capacities. In this paper, we study the fundamental upper bound of information dissemination rates with these constraints in undirected networks, given the unique replicable and encodable properties of information flows. Based on recent advances in network coding and classical modeling techniques in flow networks, we provide a natural linear programming formulation of the maximum multicast rate problem. By applying Lagrangian relaxation on the primal and the dual linear programs (LPs), respectively, we derive a) a necessary and sufficient condition characterizing multicast rate feasibility, and b) an efficient and distributed subgradient algorithm for computing the maximum multicast rate. We also extend our discussions to multiple communication sessions, as well as to overlay and ad hoc network models. Both our theoretical and simulation results conclude that, network coding may not be instrumental to achieve better maximum multicast rates in most cases; rather, it facilitates the design of significantly more efficient algorithms to achieve such optimality.
15951062
Probabilistic Power Management for Wireless Ad Hoc Networks
Extending system lifetime by effectively managing power on participating nodes is critical in wireless ad hoc networks. Recent work has shown that, by appropriately powering off nodes, energy may be significantly saved up to a factor of two, especially when node density is high. Such approaches rely on the selection of a virtual backbone (i.e., a connected dominating set) of the topology to forward ongoing traffic, coupled with algorithms to manually and periodically recompute such a backbone for load balancing purposes. The common drawback of such schemes is the need to involve periodic message exchanges and to make additional restrictive assumptions. This paper presents Odds1, an integrated set of energy-efficient and fully distributed algorithms for power management in wireless ad hoc networks. Odds build on the observation that explicit and periodic re-computation of the backbone topology is costly with respect to its additional bandwidth overhead, especially when nodes are densely populated or highly mobile. Building on a fully probabilistic approach, Odds seek to make a minimum overhead, perfectly balanced, and fully localized decision on each node with respect to when and how long it needs to enter standby mode to conserve energy. Such a decision does not rely on periodic message broadcasts in the local neighborhood, so that Odds are scalable as node density increases. Detailed mathematical analysis, discussions and simulation results have shown that Odds are indeed able to achieve our objectives while operating in a wide range of density and traffic loads.
9219226
iFlow: Middleware-assisted Rendezvous-based Information Access for Mobile Ad Hoc Applications
Due to node mobility and limitations on bandwidth availability in wireless channels, there exist unique challenges towards achieving efficient and effective information access in wireless ad hoc networks with mobile nodes. In this paper, we address two critical questions: (1) How may information be accessed with the highest degree of bandwidth efficiency? and (2) How should algorithms be designed so that node mobility contributes positively towards high performance and efficiency? We present iFlow, a middleware-based framework for bandwidth-efficient and delay-aware information access for mobile ad hoc applications. We present the case of information rendezvous, where the demands for information are satisfied by the supplies in a fully distributed fashion, across third-party nodes beyond information suppliers and consumers. Such rendezvous is achieved via controlled diffusion of information from the suppliers, matched by the gleaning process on the consumers. We validate our claims using simulation and experimental results.
5878041
sFlow: towards resource-efficient and agile service federation in service overlay networks
Existing research work towards the composition of complex federated services has assumed that service requests and deliveries flow through a particular service path or tree. Here, we extend such a service model to a directed acyclic graph, allowing services to be delivered via parallel paths and interleaved with each other. Such an assumption of the service flow model has apparently introduced complexities towards the development of a distributed algorithm to federate existing services, as well as the provisioning of the required quality in the most resource-efficient fashion. To this end, we propose sFlow, a fully distributed algorithm to be executed on all service nodes, such that the federated service flow graph is resource efficient, performs well, and meets the demands of service consumers.
6792202
Scalable streaming for heterogeneous clients
Periodic broadcast protocols enable the efficient streaming of highly popular media files to large numbers of concurrent clients. Most previous periodic broadcast protocols, however, assume that all clients can receive at the same rate, and also assume that available bandwidth is not time-varying. In this paper, we first develop a new periodic broadcast protocol, Optimized Heterogeneous Periodic Broadcast (OHPB), that can be optimized for a given population of clients with heterogeneous reception bandwidths and quality-of-service requirements. The OHPB protocol utilizes an optimized segment size progression determined by solving a linear optimization model that takes as input the client population characteristics and an objective function such as mean client startup delay. We then propose complementary client protocols employing work-ahead buffering of data during playback, so as to enable more uniform playback quality when the available bandwidth is time-varying.
206924248
The impact of topology on overlay routing service
A moderate amount of recent work has been dedicated to using overlay network to support value-added network service, such as overlay multicast, OverQoS, etc. Overlay service network is a generic service framework which is designed to provide a variety of services to overlay service customers. To design an overlay service network, the first step is to choose an overlay topology connecting all the overlay service nodes. For example, RON [Anderson, DG et al., 2001] has used full mesh topology connecting all the nodes. In this paper, we did a study on the impact of topology on the overlay routing service. We found that the overlay topology has significant impact on the overlay routing in terms of routing performance and routing overhead. For example, the full mesh topology does not always give us the best performance. Moreover, the physical topology information can benefit us a lot to construct an efficient overlay topology. In addition, some alternative topologies can provide us with better performance when considering both the routing performance and overhead.
7324721
A technique for reducing synchronization overhead in large scale multiprocessors
A b s t r a c t The effectiveness of multiprocessing a single subroutine in a tightly coupled muir!processor system is highly dependent (among other factors) on the amount of overhead incurred due to synchronized references to shared data items by active processes. In this paper we present a technique to reduce this overhead. This is achieved by reducing the number of synchronized references issued by different processes. We describe the criteria used to identify the variables whose synchronized accesses will eliminate the need to synchronize references to other variables. Our technique can be implemented in optimizing compilers for mnltiprocessor machines. It can also be used when designing parallel algorithms for multiproeessors. We implemented the technique as a pass in the Parafrase system of the University of Illinois. Relevant measurements on all the subroutines of the EISPACK package are reported (61 subroutines). The results show that our technique is quite effective. For subroutines with interprocess communication, it reduced the number of memory references requiring synchronization by 10% in two thirds of these subroutines and by more than 30% for one third of the subroutines.
32094418
On Ranks of Matrices Associated with Trees
Abstract.A sign pattern matrix is a matrix whose entries are from the set {+,−,0}. The purpose of this paper is to obtain bounds on the minimum rank of any symmetric sign pattern matrix A whose graph is a tree T (possibly with loops). In the special case when A is nonnegative with positive diagonal and the graph of A is “star-like”, the exact value of the minimum rank of A is obtained. As a result, it is shown that the gap between the symmetric minimal and maximal ranks can be arbitrarily large for a symmetric tree sign pattern A.

62173532
Efficient interprocedural analysis for program parallelization and restructuring
An approach to efficient interprocedural analysis for program parallelization and restructuring is presented. Such analysis is needed for parallelizing loops which contain procedure calls. Our approach captures call effect on data dependencies by propagating the precise information of array subscripts from the called procedure. This allows the optimizing compiler to choose an efficient yet precise data dependence test scheme depending on the complexity of array reference patterns. The other existing methods do not provide such flexibility, hence may suffer from either imprecision or inefficiency. The paper also discusses usage of classical summary information in several important transformations for program parallelization. Experimental results are reported.
1731285
A DoS Resilient Flow-level Intrusion Detection Approach for High-speed Networks
Global-scale attacks like viruses and worms are increasing in frequency, severity and sophistication, making it critical to detect outbursts at routers/gateways instead of end hosts. In this paper we leverage data streaming techniques such as the reversible sketch to obtain HiFIND, a High-speed Flow-level Intrusion Detection system. In contrast to existing intrusion detection systems, HiFIND I ) is scalable to flow-level detection on high-speed networks; 2) zs DoS resilient; 3) can distinguish SYN flooding and various port scans (mostly for worm propagation) for effective mitigation; 4 ) enables aggregate detection over multiple routers/gateways; and 5) separates anomalies to limit false positives in detection. Both theoretical analysis and evaluation with several router traces show that HiFIND achieves these properties. To the best of our knowledge, HiFIND is the first online DoS resilient flow-level intrusion detection system for high-speed networks (approximately 10s of Gigabit/second), even for the worst case trafic of 40-byte-packet streams with each packet forming a flow.