8291592
Performance analysis of the send-on-demand: A distributed database concurrency control protocol for high-speed networks
In this paper, we consider an application of high-speed wide area networks, viz. that of distributed database systems (DDBS). In a high-speed environment, although the transmission delay decreases, the propagation delay (communication latency) now becomes the throughput thwarting factor. Existing Concurrency Control (CC) protocols do not address the communication latency problem. This paper is a continuation of our research work in this area. First, we very briefly summarize our previously reported research results, viz. the issues that are important for DDBS in high-speed wide area networks, and the description of a new CC protocol called 'send-on-demand'. A detailed comparison of this protocol with that of locking is provided, using analytical and simulation techniques. The datacycle scheme performs very well in a read-oriented environment, and the rest of the paper deals with developing and comparing hybrid CC schemes using datacycling for queries. Altogether, the performance of four concurrency control schemes is compared.
14976055
A new token passing distributed mutual exclusion algorithm
Eliminating interference between concurrently executing activities through mutual exclusion is one of the most fundamental problems in computer systems. The problem of mutual exclusion in a distributed system is especially interesting owing to the lack of global knowledge in the presence of variable communication delays. In this paper, a new token-based distributed mutual exclusion algorithm is proposed. The algorithm incurs approximately three messages at high loads, irrespective of the number of nodes N in the system. At low loads, it requires approximately N messages. The paper also addresses failure recovery issues, such as token loss.
40446138
A distributed hierarchical management framework for heterogeneous WANs
The scope of network management is expanding in multiple dimensions. Local area networks (LANs) have more nodes than ever before, enterprise networks span national boundaries, wide area networks (WANs) cover the globe, and administrators want to manage their LANs all the way down to a PC’s network interface and application software. In order to centrally manage these networks, the network manager faces the complexity of heterogeneous management tools and the difficulty of managing vast amount of data generated by network elements.
13442653
Establishing virtual enterprises by means of mobile agents
Electronic commerce is expanding from the simple notion of electronic stores to the notion of virtual enterprises (VE), where existing enterprises dynamically form temporary alliances, joining their businesses in order to share their costs, skills and resources in supporting certain activities. Two fundamental problems in VE are: (1) how a VE is established, and (2) how information is shared among the VE participants in a controlled and efficient manner. Currently, existing enterprises are using workflows to automate their operations by integrating their information systems and human resources. Thus, in this paper, we view the establishment of a VE as a problem of dynamically expanding and integrating workflows in decentralized, autonomous and interacting workflow management systems. The focus is on the idea of mobile agents called "adlets" and their use in establishing VEs that involves advertising, negotiating and exchanging control information and data as well as its management.
25726525
A survey of TCP-friendly router-based AQM schemes
Although the majority of the traffic over the Internet is still TCP-based, applications such as voice over IP and video-conferencing are changing this very rapidly. While TCP-based applications react to network congestion, UDP-based streaming applications usually do not have any type of flow and congestion control mechanisms. UDP, the transport layer protocol used by audio and video streaming applications, does not react to network congestion thus stealing bandwidth from the responsive TCP-based connections. Several solutions have been suggested to combat this TCP-friendliness problem, mostly applied either in the end systems (end-to-end) at the transport layer of the protocol stack or inside the network (routers) at the network layer. This article surveys the state-of-the-art in router-based mechanisms to address the TCP-friendliness problem and presents a description of the most important algorithms, design issues, advantages and disadvantages, and a performance evaluation. The article also describes ways to estimate the number of active flows traversing a core router and points to further sources on this subject, which is widely used by many mechanisms, including several described in this survey.
30095382
Performance Analysis of Generalized Selective Packet Discarding Schemes
Selective packet discarding schemes have been mostly developed and analyzed in the context of ATM networks. However, similar schemes could be applied to non-ATM or more general networks. The analysis of selective packet discarding schemes in a general packet switching environment has been limited to the basic dropping schemes, i.e., Partial Packet Discard (PPD) and Early Packet Discard (EPD), and for only the single traffic source case. In this paper, we extend the mathematical analysis of PPD and EPD for multiple sources and include simulation results to verify the analytical results. Finally, to place the performance of the generalized EPD and PPD in the context of other packet dropping schemes, we also provide simulation results of the Drop from Front (DfF), and preemptive Partial Packet Discard (pPPD) schemes.
8561751
Partially overlapped channels not considered harmful
Many wireless channels in different technologies are known to have partial overlap. However, due to the interference effects among such partially overlapped channels, their simultaneous use has typically been avoided. In this paper, we present a first attempt to model partial overlap between channels in a systematic manner. Through the model, we illustrate that the use of partially overlapped channels is not always harmful. In fact, a careful use of some partially overlapped channels can often lead to significant improvements in spectrum utilization and application performance. We demonstrate this through analysis as well as through detailed application-level and MAC-level measurements. Additionally, we illustrate the benefits of our developed model by using it to directly enhance the performance of two previously proposed channel assignment algorithms --- one in the context of wireless LANs and the other in the context of multi-hop wireless mesh networks. Through detailed simulations, we show that use of partially overlapped channels in both these cases can improve end-to-end application throughput by factors between 1.6 and 2.7 in different scenarios, depending on wireless node density. We conclude by observing that the notion of partial overlap can be the right model of flexibility to design efficient channel access mechanisms in the emerging software radio platforms.
2969941
SmartNotes: Implicit Labeling of Meeting Data through User Note-Taking and Browsing
We have implemented SmartNotes, a system that automatically acquires labeled meeting data as users take notes during meetings and browse the notes afterwards. Such data can enable meeting understanding components such as topic and action item detectors to automatically improve their performance over a sequence of meetings. The SmartNotes system consists of a laptop based note taking application, and a web based note retrieval system. We shall demonstrate the functionalities of this system, and will also demonstrate the labeled data obtained during typical meetings and browsing sessions.
135907
Minimum energy reliable paths using unreliable wireless links
We address the problem of energy-efficient reliable wireless communication in the presence of unreliable or lossy wireless link layers in multi-hop wireless networks. Prior work [1] has provided an optimal energy efficient solution to this problem for the case where link layers implement perfect reliability. However, a more common scenario --- a link layer that is not perfectly reliable, was left as an open problem. In this paper we first present two centralized algorithms, BAMER and GAMER, that optimally solve the minimum energy reliable communication problem in presence of unreliable links. Subsequently we present a distributed algorithm, DAMER, that approximates the performance of the centralized algorithm and leads to significant performance improvement over existing single-path or multi-path based techniques.
11158
SenseRelate: : TargetWord-A Generalized Framework for Word Sense Disambiguation
Many words in natural language have different meanings when used in different contexts. Sense Relate: Target Word is a Perl package that disambiguates a target word in context by finding the sense that is most related to its neighbors according to a WordNet: Similarity measure of relatedness.
16477654
Efficient peer location on the Internet
We consider the problem of locating nearby application peers over the Internet. We define a new peer-location scheme (called Tiers), that scales to large application peer groups. Tiers creates a hierarchy of peers, and provides an efficient and scalable solution to the peer-location problem. Tiers can be implemented entirely in the application-layer and does not require the deployment of either any additional measurement services, or well-known reference points in the network.We have evaluated the performance of Tiers through detailed experiments. Our results show that Tiers is able to locate the nearest peers quickly (≪ 1 s) and accurately on wide-area Internet-like topologies. We have also compared the performance of Tiers with two other schemes, Beaconing and Distributed Binning, both of which are known to have good performance. Both these techniques are reference-points based schemes and are efficient for overlays with a small number of peers (e.g. ≤32). Our results show that Tiers significantly outperforms both these schemes. Tiers is particularly efficient for large overlay networks, has an order of magnitude lower control overhead for overlays with 512 peers and still achieves greater accuracy in locating the nearest peers.