5857841
Controlled Flooding Search with Delay Constraints
In this paper we consider the problem of query and search in a network, e.g., searching for a specific node or a piece of data. We limit our attention to the class of TTL (time-to-live) based controlled flooding search strategies where query/search packets are broadcast and relayed in the network until a preset TTL value carried in the packet expires. Every unsuccessful search attempt results in an increased TTL value (i.e., larger search area) and the same process is repeated. Every search attempt also incurs a cost (in terms of packet transmissions and receptions) and a delay (time till timeout or till the target is found). The primary goal is to derive search strategies (i.e., sequences of TTL values) that minimize a worstcase cost measure subject to a worst-case delay constraint. We present a constrained optimization framework and derive a class of optimal strategies, shown to be randomized strategies, and obtain their performance as a function of the delay constraint. We also use these results to discuss the trade-off between search cost and delay within the context of flooding search.
17234499
AMRoute: Ad Hoc Multicast Routing Protocol
The Ad hoc Multicast Routing protocol (AMRoute) presents a novel approach for robust IP Multicast in mobile ad hoc networks by exploiting user-multicast trees and dynamic logical cores. It creates a bidirectional, shared tree for data distribution using only group senders and receivers as tree nodes. Unicast tunnels are used as tree links to connect neighbors on the user-multicast tree. Thus, AMRoute does not need to be supported by network nodes that are not interested/capable of multicast, and group state cost is incurred only by group senders and receivers. Also, the use of tunnels as tree links implies that tree structure does not need to change even in case of a dynamic network topology, which reduces the signaling traffic and packet loss. Thus AMRoute does not need to track network dynamics; the underlying unicast protocol is solely responsible for this function. AMRoute does not require a specific unicast routing protocol; therefore, it can operate seamlessly over separate domains with different unicast protocols. Certain tree nodes are designated by AMRoute as logical cores, and are responsible for initiating and managing the signaling component of AMRoute, such as detection of group members and tree setup. Logical cores differ significantly from those in CBT and PIM-SM, since they are not a central point for data distribution and can migrate dynamically among member nodes. Simulation results (using ns-2) demonstrate that AMRoute signaling traffic remains at relatively low level for typical group sizes. The results also indicate that group members receive a high proportion of data multicast by senders, even in the case of a highly dynamic network.
3779394
Random waypoint considered harmful
This study examines the random waypoint model widely used in the simulation studies of mobile ad hoc networks. Our findings show that this model fails to provide a steady state in that the average nodal speed consistently decreases over time, and therefore should not be directly used for simulation. We show how unreliable results can be obtained by using this model. In particular, certain ad hoc routing metrics can drop by as much as 40% over the course of a 900-second simulation using the random waypoint model. We give both an intuitive and a formal explanation for this phenomenon. We also propose a simple fix of the problem and discuss a few alternatives. Our modified random waypoint model is able to reach a steady state and simulation results are presented.
5439484
Modeling TCP performance with proxies
This paper investigates TCP dynamics and performance over proxies that shorten the TCP feedback loop by segmenting the end-to-end connection. Such proxies are often used to improve the TCP performance, e.g. a splitting/spoofing proxy in satellite communication, and more commonly, a web cache. Through analysis, we attempt to develop a basic understanding of the properties of TCP dynamics when such proxies are used, and further obtain design principles of systems involving such proxies. We present simple models capturing some features of the proxy performance in both the lossless and lossy scenarios. Due to the complexity involved, detailed analysis is only available in the lossless scenario, and our discussion in the lossy scenario is largely limited to steady-state behavior. Nevertheless we are able to obtain useful insight. We identify conditions under which using a proxy provides significant or marginal performance gain by investigating factors including initial window size, congestion level of the proxy, and the level of asymmetry between the segments segregated by the proxy. We also discuss how these conditions affect the deployment and provisioning of such systems.
1051296
Sound mobility models
Simulation has become an indispensable tool in the construction and evaluation of mobile systems. By using mobility models that describe constituent movement, one can explore large systems, producing repeatable results for comparison between alternatives. Unfortunately, the vast majority of mobility models---including all those in which nodal speed and distance or destination are chosen independently---suffer from decay; average speed decreases until converging to some long-term average. Such decay provides an unsound basis for simulation studies that collect results averaged over time, complicating the experimental process.This paper shows via analysis that such decay is inevitable in a wide variety of mobility models, including the most common in use today. We derive a general framework for describing this decay, and apply it to a number of practical cases. Furthermore, this framework allows us to transform any given mobility model into a stationary one: choose initial speeds from the steady-state distribution, and subsequent speeds from the original. This transformation provides sound models for simulation, eliminating variations in average nodal speed.
9147389
Data-gathering wireless sensor networks: organization and capacity
In this paper we study the transport capacity of a data-gathering wireless sensor network under different communication organizations. In particular, we consider using a flat as well as a hierarchical/clustering architecture to realize many-to-one communications. The capacity of the network under this many-to-one data-gathering scenario is reduced compared to random one-to-one communication due to the unavoidable creation of a point of traffic concentration at the data collector/receiver. We introduce the overall throughput bound of λ = W/n per node, where W is the transmission capacity, and show under what conditions it can be achieved and under what conditions it cannot. When those conditions are not met, we constructively show how λ = Θ(W/n) is achieved with high probability as the number of sensors goes to infinity. We also show how the introduction of clustering can improve the throughput. We discuss the trade-offs between achieving capacity and energy consumption, how transport capacity might be affected by considering in-network processing and the implications this study has on the design of practical protocols for large-scale data-gathering wireless sensor networks.
8315730
Distributed computing
A distributed computing system consists of a collection autonomous computers connected by a communication network. The motivation for such a distributed system includes resource and load sharing, reduced costs in computation and communication, higher performance and throughput, and increased reliability and availability.
19887828
Deploying the Mobile-Agent Technology in Warehouse Management
Mobile agents, a relatively new paradigm for distributed software development, has become an accessible technology in recent years. The potential benefits of this paradigm, including the reduction of network bandwidth consumption and latency, promise to revolutionize distributed applications. 
 
This paper describes a proposed project to deploy the mobile agent technology in warehouse management.
2288132
Applying Design Patterns in Distributing a Genetic Algorithm Application
-This paper describes an experiment that employs an incremental approach to distribute a genetic algorithm application. The incremental approach allows the application to be initially developed for a standalone system, and then extended to run on multiple systems concurrently. For the extension, design patterns are employed wherever appropriate. The use of design patterns in the experiment is described, and the outcome of the experiment, including quantitative measurements, is presented.
12646584
An Evaluation of the Use of Problem-Based Learning Software By Middle School Students
Research has shown the potential of a problem-based approach to enhance students' learning. The interactive nature of hypermedia technology and its ability to deliver information in different media formats can provide unique capabilities for implementing problem-based learning (PBL) environments. Yet, we know little about the types of tools that are effective in supporting students' learning in a hypermedia supported PBL environment. The purpose of this study was to investigate both the use of tools and design features in a piece of PBL software and their effectiveness on middle school students' learning. The findings of this study show that students who were exposed to the PBL environment increased their achievement scores from pre to posttest more than those students who learned the same content in the traditional classroom. Students' reading ability was found to be a better predictor for their achievement in PBL than their math ability. However, the brief treatment of the study had only limited impact on students' attitude toward learning science. The findings of the study and their implications are discussed in detail.
18228951
Combinatorial constructions for optimal supersaturated designs
Abstract Combinatorial designs have long had substantial application in the statistical design of experiments, and in the theory of error-correcting codes. Applications in experimental and theoretical computer science, communications, cryptography and networking have also emerged in recent years. In this paper, we focus on a new application of combinatorial design theory in experimental design theory. E ( f NOD ) criterion is used as a measure of non-orthogonality of U-type designs, and a lower bound of E ( f NOD ) which can serve as a benchmark of design optimality is obtained. A U-type design is E ( f NOD )-optimal if its E ( f NOD ) value achieves the lower bound. In most cases, E ( f NOD )-optimal U-type designs are supersaturated. We show that a kind of E ( f NOD )-optimal designs are equivalent to uniformly resolvable designs. Based on this equivalence, several new infinite classes for the existence of E ( f NOD )-optimal designs are then obtained.