22674996
Estimating Link Characteristics of Internet Paths With FPathchar
RESEARCH PROJECTS Understanding the design tradeoffs of cooperative streaming multicast: Cooperative end-system multicast (CEM) is emerging as a promi sing paradigm for video distribution since the bandwidth overhead of dissemi nating content is shared among the participants themselves. Prior research in CEMs h as focused either on the design of new protocols or on comparisons of complete sys tems. However, the inherent tradeoffs between different CEM designs, particu larly under a wide range of operating conditions, are not well understood. In this wo rk [1], we empirically and systematically evaluate CEM design choices. We synthes ize our results into a model that captures the inherent tradeoffs in CEMs, which i n particular, conjectures that no CEM design can simultaneously achieve low over head, low lag, and high streaming quality.
32945610
A Framework for Automatic Identification of the Best Checkpoint and Recovery Protocol
Fault tolerance is important for a distributed system to increase its reliability and throughput. Checkpoint and recovery protocols have been proposed as fault tolerance for non-critical applications. The performance of checkpoint and recovery protocols plays an important role in the overall performance of a distributed system. The performance of these protocols depends on system characteristics as well as an application characteristics. In this paper, we propose a novel technique to automatically identify the checkpoint and recovery protocol which is likely to perform the best for a given system and an application the system is currently running. We present experimental results to show that the scheme can efficiently determine a suitable checkpoint and recovery protocol for many applications.
19017935
Fault-containing network protocols
Self-stabilization is a simple and elegant approach towards designing fault-tolerant network protocols. While self-stabilization provides automatic recovery from arbitrary transient faults, self-stabilizing systems do not incorporate any optimization for more efficient recovery from limited transient faults, even though such limited faults are more likely to occur in practice than arbitrary faults. Fault-containing self-stabilizing protocols are proposed to efficiently contain the effects of more frequent, limited transient faults while retaining the desirable property of self-stabilization. In this paper, we propose a methodology for designing fault-containing selfstabilizing network protocols. The methodology views the properties of self-stabilization and fault-containment in separation. Since self-stabilizing protocols already exist for many important network problems, the design starts with an existing self-stabilizing protocol, and adds to it the fault-containment property. The feasibilitv of this technique is illustrated bv the design of a fault-containing self-stabilizing protocol for the breadthfirst-search (BFS) spanning tree problem. The applicability of the technique used in deriving the BFS protocol to other problems is also discussed.
65058359
Group Based Routing in Disconnected Ad Hoc Networks
In this paper, we propose a routing protocol for disconnected ad hoc networks where most nodes tend to move about in groups. To the best of our knowledge, no routing protocol for disconnected ad hoc networks has been designed earlier keeping in mind possible group patterns formed by the movement of nodes. Our protocol works by identifying groups using an efficient distributed group membership protocol, and then routing at the group level, rather than at the node level. The protocol is designed so that existing concepts of routing in disconnected ad hoc networks can be extended to work at the group level. Initial simulations across a broad spectrum of parameters suggest that our protocol performs better in terms of delivery ratio and latency over traditional approaches like AODV [1], and also over disconnected routing approaches like the 2-Hop routing protocol [2].
1713935
Designing Caching Strategies for Common NFS Workloads
9811083
Performance enhancement of a contract net protocol based system through instance-based learning
The contract net protocol (CNP) is a widely used coordination mechanism in multiagent systems. It has a lot of communication overhead due to the broadcast of the task announcements. The performance of the CNP degrades drastically when the number of communicating agents and the number of tasks announced increases. Hence, it has problems of scalability. In order to overcome this limitation, an instance-based learning (IBL) mechanism is designed that uses previously stored instances in order to select a target agent. This avoids the expensive bidding process. The scheme is implemented in a simulated distributed hospital system where the CNP is used for resource sharing across hospitals. Experimental results demonstrate that with the incorporation of the IBL, the system performance improves significantly. The system is better scalable with respect to the number of tasks.
1019520
Vertex Partitioning Problems On Partial k-Trees
We describe a general approach to obtain polynomial-time algorithms over partial k-trees for graph problems in which the vertex set is to be partitioned in some way. We encode these problems with formulae of the Extended Monadic Second-order (or EMS) logic. Such a formula can be translated into a polynomial-time algorithm automatically. We focus on the problem of partitioning a partial k-tree into induced subgraphs isomorphic to a fixed pattern graph; a distinct algorithm is derived for each pattern graph and each value of k. We use a “pumping lemma” to show that (for some pattern graphs) this problem cannot be encoded in the “ordinary” Monadic Second-order logic—from which a linear-time algorithm over partial k-trees would be obtained. Hence, an EMS formula is in some sense the strongest possible. As a further application of our general approach, we derive a polynomial-time algorithm to determine the maximum number of co-dominating sets into which the vertices of a partial k-tree can be partitioned. (A co-dominating set of a graph is a dominating set of its complement graph).
6989341
Navigating Virtual Information Sources with Know-ME
In many application domains such as biological sciences, information integration faces a challenge usually not observed in simpler applications. Here, the tobe-integrated information sources come from very different sub-specialties (e.g., anatomy and behavioral neuroscience) and have widely diverse schema, often with little or no overlap in attributes. Yet, they can be conceptually integrated because they refer to different aspects of the same physical objects or phenomena. We have proposed model-based mediation (MBM) as an information integration paradigm where information sources with hard-to-correlate schemas may be integrated using auxiliary expert knowledge to hold together widely different data schemas. The expert knowledge is captured in a graph structure called the Knowledge Map. In MBM, we extend the global-as-view architecture by lifting exported source data to conceptual models (CMs) that represent more source specific knowledge than a logical schema. The mediator's IVDs are defined in terms of source CMs and make use of a semantically richer model involving class hierarchies, complex object structure, and rule-defined semantic integrity constraints. Additionally, sources specify object contexts, i.e., formulas that relate a source's conceptual schema with the global domain knowledge maintained at the mediator. In this paper, we introduce a tool called Knowledge Map Explorer (Know-ME) for a user to explore both the domain knowledge, and all data sources that have been integrated using it.
193663
SAT-Based Image Computation with Application in Reachability Analysis
Image computation nds wide application in VLSI CAD, such as state reachability analysis in formal veri cation and synthesis, combinational veri cation, combinational and sequential test. Existing BDD-based symbolic algorithms for image computation are limited by memory resources in practice, while SAT-based algorithms that can obtain the image by enumerating satisfying assignments to a CNF representation of the Boolean relation are potentially limited by time resources. We propose new algorithms that combine BDDs and SAT in order to exploit their complementary bene ts, and to o er a mechanism for trading o space vs. time. In particular, (1) our integrated algorithm uses BDDs to represent the input and image sets, and a CNF formula to represent the Boolean relation, (2) a fundamental enhancement called BDD Bounding is used whereby the SAT solver uses the BDDs for the input set and the dynamically changing image set to prune the search space of all solutions, (3) BDDs are used to compute all solutions below intermediate points in the SAT decision tree, (4) a ne-grained variable quanti cation schedule is used for each BDD subproblem, based on the CNF representation of the Boolean relation. These enhancements coupled with more engineering heuristics lead to an overall algorithm that can potentially handle larger problems. This is supported by our preliminary results on exact reachability analysis of ISCAS benchmark circuits.
11289392
Efficient Routing for Peer-to-Peer Overlays
Most current peer-to-peer lookup schemes keep a small amount of routing state per node, typically logarithmic in the number of overlay nodes. This design assumes that routing information at each member node must be kept small, so that the bookkeeping required to respond to system membership changes is also small, given that aggressive membership dynamics are expected. As a consequence, lookups have high latency as each lookup requires contacting several nodes in sequence. 
 
In this paper, we question these assumptions by presenting two peer-to-peer routing algorithms with small lookup paths. First, we present a one-hop routing scheme. We show how to disseminate information about membership changes quickly enough so that nodes maintain accurate routing tables with complete membership information. We also deduce analytic bandwidth requirements for our scheme that demonstrate its feasibility. 
 
We also propose a two-hop routing scheme for large scale systems of more than a few million nodes, where the bandwidth requirements of one-hop routing can become too large. This scheme keeps a fixed fraction of the total routing state on each node, chosen such that the first hop has low latency, and thus the additional delay is small. 
 
We validate our analytic model using simulation results that show that our algorithms can maintain routing information sufficiently up-to-date such that a large fraction (e.g., 99%) of the queries will succeed without being re-routed.
25366029
Formal hardware verification methods: A survey
Growing advances in VLSI technology have led to an increased level of complexity in current hardware systems. Late detection of design errors typically results in higher costs due to the associated time delay as well as loss of production. Thus it is important that hardware designs be free of errors. Formal verification has become an increasingly important technique towards establishing the correctness of hardware designs. In this article we survey the research that has been done in this area, with an emphasis on more recent trends. We present a classification framework for the various methods, based on the forms of the specification, the implementation, and the proff method. This framework enables us to better highlight the relationships and interactions between seemingly different approaches.