15267355
A-DRAFT: an adaptive QoS mechanism to support absolute and relative throughput in 802.11 wireless LANs
Several distributed QoS mechanisms have been proposed to augment the existing distributed coordination function of the IEEE 802.11 MAC protocol to provide QoS support for QoS-sensitive applications. These mechanisms use well-known QoS enabling techniques such as priority assignment and fair scheduling within existing 802.11 MAC parameters. Although these mechanisms provide differentiated throughput for different classes of traffic, they cannot provide both relative and absolute throughput support simultaneously.In this paper, we propose a new mechanism called A-DRAFT that supports both absolute and relative throughput in an adaptive and a fully distributed manner. This paper describes an adaptive mechanism that supports absolute throughput as long as the total demand from this class is below the effective channel capacity. The proposed mechanism also provides relative or fair throughput support with low variation and a high degree of fairness even in a saturated network with a large number of MSs. We make use of deficit round robin scheduling with different levels of quantum rate to provide fairness, and different weights to provide absolute and relative throughput. We evaluate the performance of the proposed mechanism via mathematical analysis and confirm this analysis with simulations.
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.
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.
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.
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.
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.
2759775
Distributed channel management in uncoordinated wireless environments
Wireless 802.11 hotspots have grown in an uncoordinated fashion with highly variable deployment densities. Such uncoordinated deployments, coupled with the difficulty of implementing coordination protocols, has often led to conflicting configurations (e.g., in choice of transmission power and channel of operation) among the corresponding Access Points (APs). Overall, such conflicts cause both unpredictable network performance and unfairness among clients of neighboring hotspots. In this paper, we focus on the fairness problem for uncoordinated deployments. We study this problem from the channel assignment perspective. Our solution is based on the notion of channel-hopping, and meets all the important design considerations for control methods in uncoordinated deployments - distributed in nature, minimal to zero coordination among APs belonging to different hotspots, simple to implement, and interoperable with existing standards. In particular, we propose a specific algorithm called MAXchop, which works efficiently when using only non-overlapping wireless channels, but is particularly effective in exploiting partially-overlapped channels that have been proposed in recent literature. We also evaluate how our channel assignment approach complements previously proposed carrier sensing techniques in providing further performance improvements. Through extensive simulations on real hotspot topologies and evaluation of a full implementation of this technique, we demonstrate the efficacy of these techniques for not only fairness, but also the aggregate throughput, metrics.We believe that this is the first work that brings into focus the fairness properties of channel hopping techniques and we hope that the insights from this research will be applied to other domains where a fair division of a system's resources is an important consideration.
11368060
Packet classifiers in ternary CAMs can be smaller
Serving as the core component in many packet forwarding, differentiating and filtering schemes, packet classification continues to grow its importance in today's IP networks. Currently, most vendors use Ternary CAMs (TCAMs) for packet classification. TCAMs usually use brute-force parallel hardware to simultaneously check for all rules. One of the fundamental problems of TCAMs is that TCAMs suffer from range specifications because rules with range specifications need to be translated into multiple TCAM entries. Hence, the cost of packet classification will increase substantially as the number of TCAM entries grows. As a result, network operators hesitate to configure packet classifiers using range specifications. In this paper, we optimize packet classifier configurations by identifying semantically equivalent rule sets that lead to reduced number of TCAM entries when represented in hardware. In particular, we develop a number of effective techniques, which include: trimming rules, expanding rules, merging rules, and adding rules. Compared with previously proposed techniques which typically require modifications to the packet processor hardware, our scheme does not require any hardware modification, which is highly preferred by ISPs. Moreover, our scheme is complementary to previous techniques in that those techniques can be applied on the rule sets optimized by our scheme. We evaluate the effectiveness and potential of the proposed techniques using extensive experiments based on both real packet classifiers managed by a large tier-1 ISP and synthetic data generated randomly. We observe significant reduction on the number of TCAM entries that are needed to represent the optimized packet classifier configurations.
6727358
Segmenting meetings into agenda items by extracting implicit supervision from human note-taking
Splitting a meeting into segments such that each segment contains discussions on exactly one agenda item is useful for tasks such as retrieval and summarization of agenda item discussions. However, accurate topic segmentation of meetings is a difficult task. In this paper, we investigate the idea of acquiring implicit supervision from human meeting participants to solve the segmentation problem. Specifically we have implemented and tested a note taking interface that gives value to users by helping them organize and retrieve their notes easily, but that also extracts a segmentation of the meeting based on note taking behavior. We show that the segmentation so obtained achieves a Pk value of 0.212 which improves upon an unsupervised baseline by 45% relative, and compares favorably with a current state-of-the-art algorithm. Most importantly, we achieve this performance without any features or algorithms in the classic sense.
7265407
A Database Platform for Bioinformatics
In recent years, new developments in genetics have generated a lot of interest in genomic and proteomic data, investing international significance (and competition) in the fledgling discipline of bioinformatics. Researchers in pharmaceutical and biotech companies have found that database products can bring a wide range of relevant technologies to bear on their problems. Benefiting from a number of new technology enhancements, Oracle has emerged as a popular platform for pharmaceutical knowledge management and bioinformatics. We look at four powerful technologies that show promise for solving hitherto intractable problems in bioinformatics: the extensibility architecture to store gene sequence data natively and perform high-dimensional structure-searches in the database; warehousing technologies and data mining on genetic patterns; data integration technologies to enable heterogeneous queries across distributed biological sources, and internet portal technologies that allow life sciences information to be published and managed across intranets and the internet.
3056111
An Analysis of Wireless Network Coding for Unicast Sessions: The Case for Coding-Aware Routing
A recent approach, COPE, for improving the throughput of unicast traffic in wireless multi-hop networks exploits the broadcast nature of the wireless medium through opportunistic network coding. In this paper, we analyze throughput improvements obtained by COPE-type network coding in wireless networks from a theoretical perspective. We make two key contributions. First, we obtain a theoretical formulation for computing the throughput of network coding on any wireless network topology and any pattern of concurrent unicast traffic sessions. Second, we advocate that routing be made aware of network coding opportunities rather than, as in COPE, being oblivious to it. More importantly, our work studies the tradeoff between routing flows "close to each other" for utilizing coding opportunities and "away from each other" for avoiding wireless interference. Our theoretical formulation provides a method for computing source-destination routes and utilizing the best coding opportunities from available ones so as to maximize the throughput. We handle scheduling of broadcast transmissions subject to wireless transmit/receive diversity and link interference in our optimization framework. Using our formulations, we compare the performance of traditional unicast routing and network coding with coding-oblivious and coding-aware routing on a variety of mesh network topologies, including some derived from contemporary mesh network testbeds. Our evaluations show that a route selection strategy that is aware of network coding opportunities leads to higher end-to-end throughput when compared to coding-oblivious routing strategies.