2426770
MMSN: Multi-Frequency Media Access Control for Wireless Sensor Networks
Multi-frequency media access control has been well understood in general wireless ad hoc networks, while in wireless sensor networks, researchers still focus on single frequency solutions. In wireless sensor networks, each device is typically equipped with a single radio transceiver and applications adopt much smaller packet sizes compared to those in general wireless ad hoc networks. Hence, the multi-frequency MAC protocols proposed for general wireless ad hoc networks are not suitable for wireless sensor network applications, which we further demonstrate through our simulation experiments. In this paper, we propose MMSN, which takes advantage of multi-frequency availability while, at the same time, takes into account the restrictions in wireless sensor networks. In MMSN, four frequency assignment options are provided to meet different application requirements. A scalable media access is designed with efficient broadcast support. Also, an optimal non-uniform backoff algorithm is derived and its lightweight approximation is implemented in MMSN, which significantly reduces congestion in the time synchronized media access design. Through extensive experiments, MMSN exhibits prominent ability to utilize parallel transmission among neighboring nodes. It also achieves increased energy efficiency when multiple physical frequencies are available.
1650647
Load balancing in bounded-latency content distribution
In this paper we present a balanced data replication scheme that provides real-time latency bounds on content retrieval in content distribution networks. Many network applications have ever-increasing requirements on latency sensitive data services. Data replication services have been widely used as an important performance enhancement mechanism to reduce data access latency and throughput. We investigate the problem of provisioning an underlying balanced data replication service to provide a global latency bound on data retrieval in content distribution networks. The solution involves constructing an overlay network based on the given latency bound, and a mechanism to assign content objects to the network nodes so that the workload of all the network nodes is balanced. Our evaluation results drawn from detailed simulations show the efficacy of our load-balancing scheme in meeting the latency bound requirements with high confidence under heavy load
1236122
Range-free localization and its impact on large scale sensor networks
With the proliferation of location dependent applications in sensor networks, location awareness becomes an essential capability of sensor nodes. Because coarse accuracy is sufficient for most sensor network applications, solutions in range-free localization are being pursued as a cost-effective alternative to more expensive range-based approaches. In this paper, we present APIT, a novel localization algorithm that is range-free. We show that our APIT scheme performs best when an irregular radio pattern and random node placement are considered, and low communication overhead is desired. We compare our work, via extensive simulation, with three state-of-the-art range-free localization schemes to identify the preferable system configurations of each. In addition, we provide insight into the impact of localization accuracy on various location dependent applications and suggestions on improving their performance in the presence of such inaccuracy.
8545280
EnviroStore: A Cooperative Storage System for Disconnected Operation in Sensor Networks
This paper presents a new cooperative storage system for sensor networks geared for disconnected operation (where sensor nodes do not have a connected path to a basestation). The goal of the system is to maximize its data storage capacity by appropriately distributing storage utilization and opportunistically offloading data to external devices when possible. The system is motivated by the observation that a large category of sensor network applications, such as environmental data logging, does not require real-time data access. Such networks generally operate in a disconnected mode. Rather than focusing on multihop routing to a basestation, an important concern becomes (i) to maximize the effective storage capacity of the disconnected sensor network such that it accommodates the most data, and (ii) to take the best advantage of data upload opportunities when they become available to relieve network storage. The storage system described in this paper achieves the above goals, leading to significant improvements in the amount of data collected compared to non-cooperative storage. It is implemented in nesC for TinyOS and evaluated in TOSSIM through various application scenarios.
16039010
Design, Implementation and Evaluation of a Real-Time Active Content Distribution Service
The phenomenal growth of the world-wide web has made it the most popular Internet application today. Web caching and content distribution services have been recognized as valuable techniques to mitigate the explosion of web traffic. An increasing fraction of web traffic today is dynamically generated and therefore intrinsically difficult to replicate or cache using present static approaches. Scalable delivery of such active content poses a myriad of challenges, including content replication, update propagation, and consistency management. This paper makes two contributions: it (1) describes a scalable architecture for transparent demand-driven distribution of active content; and (2) presents a system that can provide real-time delay guarantees on content access. Our approach involves migrating the scripts which generate dynamic web traffic, and their data, from the origin servers to active content distribution proxies nearest to the clients. We also present mechanisms on these proxies to enforce real-time delay guarantees for client requests. Our system is implemented and deployed on Planetlab (2004), a real-world distributed Internet testbed. Experimental data show that significant improvements are observed in effective throughput and client response time, and that delay bounds on content access can be guaranteed with a very high probability.
14725341
Towards content distribution networks with latency guarantees
This paper investigates the performance of a content distribution network designed to provide bounded content access latency. Content can be divided into multiple classes with different configurable per-class delay bounds. The network uses a simple distributed algorithm to dynamically select a subset of its proxy servers for different classes such that a global per-class delay bound is achieved on content access. The content distribution algorithm is implemented and tested on PlanetLab, a world-wide distributed Internet testbed. Evaluation results demonstrate that despite Internet delay variability, subsecond delay bounds (of 200-500ms) can be guaranteed with a very high probability at only a moderate content replication cost. The distribution algorithm achieves a 4 to 5 fold reduction in the number of response-time violations compared to prior content distribution approaches that attempt to minimize average latency. This paper presents the first wide-area performance evaluation of an algorithm designed to bound maximum content access latency, as opposed to optimizing an average performance metric.
10023746
Test and diagnosis of word-oriented multiport memories
Conventionally, the test of multiport memories is considered difficult because of the complex behavior of the faulty memories and the large number of inter-port faults. This paper presents an efficient approach for testing and diagnosing multiport RAMs. Our approach takes advantage of the higher access bandwidth due to the increased number of read/write ports, which also provides higher observability and controllability that effectively reduces the test time. Our key idea is that a sequence of March operations for any memory cell can be folded and executed within a single access cycle. We have also developed an efficient test algorithm for port-specific faults as well as traditional cell faults. The port-specific faults include the stuck-open, address decoder, and inter-port faults, for both bit-oriented and word-oriented RAMs. Experimental results for our folding scheme show that the test time reduction is about 28% for a commercial 8 KB embedded SRAM. An efficient diagnostic algorithm is also proposed for the port-specific faults and traditional cell faults.
392551
Finding Target Language Correspondence for Lexicalized EBMT System
This paper presents a three-phase approach to find the correspondence in Target Language (TL) sentence for a fragment of Source Language (SL) sentence in a lexicalized EBMT system. To be practical, it exploits surface information as much as possible instead of using parsers. Experiments show that, although not so perfect, it is very robust and effective. The three phases are: First, align the sentence pair at word level in order to provide anchors for phrase alignment. Second, based on the aligned anchors, find all the TL fragments which may possibly correspond to a SL fragment. And finally, using a score function, select the best TL fragment as the correspondence of a SL fragment.
6313307
On the Security and Vulnerability of PING
We present a formal specification of the PING protocol, and use three concepts of convergence theory, namely closure, convergence, and protection, to show that this protocol is secure against weak adversaries (and insecure against strong ones). We then argue that despite the security of PING against weak adversaries, the natural vulnerability of this protocol (or of any other protocol for that matter) can be exploited by a weak adversary to launch a denial of service attack against any computer that hosts the protocol. Finally, we discuss three mechanisms, namely ingress filtering, hop integrity, and soft firewalls that can be used to prevent denial of service attacks in the Internet.
19145806
An adaptive architecture for multi-stream authoring and presentations in distributed networks
New global trends in communications technology and liberalization are forcing dramatic changes in our lives. Applications tend to be lightweight and mobile, resulting in greater convenience. We present a new architecture to advance the traditional authoring system towards these trends. In the proposed architecture, the authoring system is capable of editing media content distributed in the networks. It forms a new model of authoring, i.e., the distributed authoring model. The distributed authoring model is described and compared with the traditional authoring model. We introduce quality-on-demand streaming in the architecture for the purpose of distributed authoring. Furthermore, we address the problems of applying multiple source streaming and quality adaptation in the architecture and show our design for resolving these problems. An implementation conforming to this architecture is also described.
60476874
High-level synthesis using computation-unit integrated memories
High-level synthesis (HLS) of memory-intensive applications has featured several innovations in terms of enhancements made to the basic memory organization and data layout. However, increasing performance and energy demands faced by application-specific integrated circuits (ASIC) are forcing designers to alter the fundamental architectural template of the HLS output, namely, a controller-datapath associated with a memory subsystem (monolithic, banked, etc.). We propose an architectural template for the HLS output that consists of a controller-datapath circuit associated with a memory subsystem into which computation units have been integrated. The enhanced memory subsystem is called computation-unit integrated memory (CIM). A CIM offers higher memory bandwidth (relative to what is offered through the system bus) to computation units present locally within it and reduces the overall communication between the memory subsystem and the controller-datapath, thus providing a template highly suitable for deriving efficient implementations of memory-intensive applications. This work addresses the challenge of providing an automatic synthesis framework for a CIM-based architecture. Our framework can analyze the various trade-offs involved in selecting suitable operations in a behavior for execution using a CIM and generate a high-performance, low-overhead implementation. Experiments with several behaviors indicate that an average performance improvement of 1.88/spl times/ (a maximum of 2.63/spl times/) is possible with very low area overheads. The energy-delay product improves by an average of 2.1/spl times/ (maximum of 3.4/spl times/).