16187298
DIRAC: a software-based wireless router system
Routers are expected to play an important role in the IP-based wireless data network. Although a substantial number of techniques have been proposed to improve wireless network performance under dynamic wireless channel conditions and host mobility, a system support framework is still missing. In this paper, we describe DIRAC, a software-based router system that is designed for wireless networks to facilitate the implementation and evaluation of various channel-adaptive and mobility-aware protocols. DIRAC adopts a distributed architecture that is composed of two parts: a Router Core (RC) shared by the wireless subnets, and a Router Agent (RA) at each access point/base station. RAs expose wireless link-layer information to the RC and enforce the control commands issued by the RC. This approach allows the router to make adaptive decisions based on link-layer information feedback. It also permits the router to enforce its policies (e.g., policing) more effectively through underlying link-layer mechanisms. As showcases, we implement under DIRAC the prototypes of three wireless network services: link-layer assisted fast handover, channel-adaptive scheduling, and link-layer enforced policing. Our implementation and experiments show that our distributed wireless router provides a flexible framework, which enables advanced network-layer wireless services that are adaptive to channel conditions and host mobility.
11410811
Fair scheduling in wireless packet networks
Fair scheduling of delay and rate-sensitive packet flows over a wireless channel is not addressed effectively by most contemporary wireline fair-scheduling algorithms because of two unique characteristics of wireless media: (1) bursty channel errors and (2) location-dependent channel capacity and errors. Besides, in packet cellular networks, the base station typically performs the task of packet scheduling for both downlink and uplink flows in a cell; however, a base station has only a limited knowledge of the arrival processes of uplink flows. We propose a new model for wireless fair-scheduling based on an adaptation of fluid fair queueing (FFQ) to handle location-dependent error bursts. We describe an ideal wireless fair-scheduling algorithm which provides a packetized implementation of the fluid mode, while assuming full knowledge of the current channel conditions. For this algorithm, we derive the worst-case throughput and delay bounds. Finally, we describe a practical wireless scheduling algorithm which approximates the ideal algorithm. Through simulations, we show that the algorithm achieves the desirable properties identified in the wireless FFQ model.
23906830
PEAS: a robust energy conserving protocol for long-lived sensor networks
Small, inexpensive sensors with limited memory, computing power and short battery lifetimes are turning into reality. Due to adverse conditions such as high noise levels, extreme humidity or temperatures, or even destructions from unfriendly entities, sensor node failures may become norms rather than exceptions in real environments. To be practical, sensor networks must last for much longer times than that of individual nodes, and have yet to be robust against potentially frequent node failures. This paper presents the design of PEAS, a simple protocol that can build a long-lived sensor network and maintain robust operations using large quantities of economical, short-lived sensor nodes. PEAS extends system functioning time by keeping only a necessary set of sensors working and putting the rest into sleep mode. Sleeping ones wake up now and then, probing the local environment and replacing failed ones. The sleeping periods are self-adjusted dynamically, so as to keep the sensors' wakeup rate roughly constant, thus adapting to high node densities.
2219088
A self-coordinating approach to distributed fair queueing in ad hoc wireless networks
Distributed fair queueing in shared-medium ad hoc wireless networks is non-trivial because of the unique design challenges in such networks, such as location-dependent contention, distributed nature of ad hoc fair queueing, channel spatial reuse, and scalability in the presence of node mobility. In this paper, we seek to devise new distributed, localized, scalable and efficient solutions to this problem. We first analyze an ideal centralized fair queueing algorithm developed for ad hoc networks, and extract the desired global properties that the localized algorithms should possess. We then propose three localized fair queueing models, in which local schedulers self-coordinate their local interactions and collectively achieve the desired global properties. We further describe a novel implementation of the proposed models within the framework of the popular CSMA/CA paradigm and address several practical issues. Our simulations and analysis demonstrate the effectiveness of our proposed design.
1236934
A Packet Scheduling Approach to QoS Support in Multihop Wireless Networks
Providing packet-level quality of service (QoS) is critical to support both rate-sensitive and delay-sensitive applications in bandwidth-constrained, shared-channel, multihop wireless networks. Packet scheduling has been a very popular paradigm to ensure minimum throughput and bounded delay access for packet flows. This work describes a packet scheduling approach to QoS provisioning in multihop wireless networks. Besides minimum throughput and delay bounds for each flow, our scheduling disciplines seek to achieve fair and maximum allocation of the shared wireless channel bandwidth. However, these two criteria can potentially be in conflict in a generic-topology multihop wireless network where a single logical channel is shared among multiple contending flows and spatial reuse of the channel bandwidth is possible. In this paper, we propose a new scheduling model that addresses this conflict. The main results of this paper are the following: (a) a two-tier service model that provides a minimum “fair” allocation of the channel bandwidth for each packet flow and additionally maximizes spatial reuse of bandwidth, (b) an ideal centralized packet scheduling algorithm that realizes the above service model, and (c) a practical distributed backoff-based channel contention mechanism that approximates the ideal service within the framework of the CSMA/CA protocol.
16959990
A wireless fair service algorithm for packet cellular networks
Wireless Fair Service Algorithm For Packet Cellular Networks Sonwu Lu Thyagarajan Nandagopal Vaduvur Bharghavan Coordinated Science Laboratory University of Illinois email: {sIu, thyagu, bharghav}~timely. crhc .uiuc. edu b order to support diverse communication-intensive redtirne and non red-time data flows over a scarce, varying and shared wireless channel with location-dependent and bursty errors, we defie a service model that has the following charxteristi~ short-tern fairness among flows which perceive a clean channel, worst-case delay bounds for packets, short-term throughput bounds for flows with clean channels and Iong-tem throughput bounds for dl flows with bounded channel error, optimal schedulable region, and support for both delay sensitive and error sensitive data flows. We present a wireless fair service algorithm, and show that it achieves the requirements of the service model through both analysis and simulation. The key aspects of the dg~ rithm are the following (a) an enhanced fair queueing based service scheme that supports decoupling of delay and bandwidth, (b) graceful service compensation for lagging flows and graceful service degradation for leading flows, (c) support for red-time delay sensitive flows as well as non realtime error sensitive flows, and (d) implementation of the wireless fair service rdgorithm within the fiarnework of the simple and robust CSMA/CA wireless medium access pro tocol.
17978140
Completeness and realizability: conditions for automatic generation of workflows
In recent years, workflow technology has greatly facilitated business process modeling and reengineering in information systems. On one hand, the separation of an application's control structure from the implementation of its task programs simplifies and speeds up application development. On the other hand, the run-time system assists users in coordinating and scheduling tasks of a business process. As a result, the cost of doing business is reduced, and business enterprises become more responsive to new business requirements and opportunities, hence, become more competitive in the market. Several formal methods have been proposed for specifying and modeling workflows. However, most workflows are designed manually, which becomes a time-consuming and error-prone procedure when a workflow involves hundreds or thousands of task programs. A recent approach is to generate workflow automatically from a task library and a specification of the desired outcome. In this paper, we define the notions of positive and negative dependency graphs for a task library to represent the dependencies among tasks in the library. Based on these dependencies, we identified sufficient conditions for a task library to be complete, and the conditions for a workflow postcondition to be realizable from a task library. We also identified a sufficient and necessary condition for the completeness of a class of task libraries, called S-task libraries.
35964038
Learning Engineering Models with the Minimum Description Length Principle
This paper discusses discovery of mathematical models from engineering data sets. KEDS, a Knowledge-based Equation Discovery System, identifies several potentially overlapping regions in the problem space, each associated with an equation of different complexity and accuracy. The minimum description length principle, together with the KEDS algorithm, is used to guide the partitioning of the problem space. The KEDSMDL algorithm has been tested on discovering models for predicting the performance efficiencies of an internal combustion engine.
1093389
TOPS: An intelligent associate for Turning Operation Planning
This article describes the development of a new modeling environment that supports the building of intelligent associates for turning operation planning. By intelligent associates, we mean a computer-based system that allows a process planner to assert a greater degree of control during a consultation than do traditional expert systems. Intelligent associates are able to assist process planners in a colleague-like manner while solving domain tasks. They relieve routine operations while supporting creative problem-solving. Multiple levels of human experience are supported, advising and constraining inexperienced planners while providing a flexible environment for experienced planners working on new planning strategies. Several Al-based techniques have been employed in the development of this new modeling environment. The utility of this environment is demonstrated by developing a turning operation planning intelligent associate (TOPS). TOPS assists a process planner by computing interactions and checking f...
15553830
A distributed artificial intelligence approach to integrated engineering design
This paper reports the development of a computer-based integrated engineering design environment which facilitates design decision-making by providing a medium for increased communication and cooperation amongst product development participants. A refinement and constraint propagation model for product development is used within a distributed artificial intelligence (DAI) architecture to support the cooperative design effort. Within such an environment, product and process designers can integrate the recommendations and expertise of all product development concerns as early as possible within the design-cycle. Our prototype system, ENVIED (Environment for Integrated Engineering Design), provides a domain-independent framework for human designers, artificial intelligence systems, and traditional software systems to cooperatively perform product and process design.
30892527
On Design and Implementation of Adaptive Data Classification Scheme for DSM Systems
Distributed Shared Memory (DSM) environment is built by using specific softwares, to combine a number of computer hardware resources into one computing environment. Such environment not only provides an easy way to execute parallel applications, but also combines resources to speedup execution of these applications. DSM systems need to maintain data consistency in memory, what usually leads to communication overhead. Therefore, there exist a number of strategies that can be used to overcome this overhead and improve overall performance. Prefetching strategies have been proven to show great performance in DSM systems, since they can reduce data access communication latencies from remote nodes. However, these strategies also transfer unnecessary prefetching pages to remote nodes. In this research paper, we focus on the analysis of data access pattern during execution of parallel applications. We propose an Adaptive Data Classification scheme to improve prefetching strategy, with the goal to improve overall performance. Adaptive Data Classification scheme classifies data according to the access behavior of pages, so that home node uses past history access patterns of remote nodes to decide whether it needs to transfer related pages to remote nodes. From experimental results, our method can improve the performance of prefetching strategies in DSM systems.