20080343
A survey of adaptive bandwidth control algorithms
In packet-switched network traffic management and control, efficiently allocating bandwidth to provide quantitative packet-level QoS to aggregate traffic has been difficult due to unpredictable, unknown statistical characteristics of the aggregate traffic. With inaccurate traffic information, using static bandwidth allocation results in the network being underutilized, or the QoS requirement not being satisfied. An alternative is to use adaptive bandwidth control (ABC), whereby the allocated bandwidth is regularly adjusted over the packet-level time scale to attain a given QoS requirement. This paper provides a literature review of ABC algorithms that guarantee aggregate traffic packet-level QoS metrics, such as the average queue length, packet loss, and packet delay. We describe different ABC algorithms, identify their advantages and shortcomings, and provide some comparative performance evaluation results. Open issues in ABC for future research directions are also discussed.
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.
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.
12875295
A comparison of multicast feedback control mechanisms
In reliable multicast applications, packet loss needs to be reported by having group members send feedback messages. This results in the well-known feedback implosion problem. The available feedback control mechanisms can be classified as timer-based, hierarchy-based and router-assisted, among which the timer-based approach is more preferable due to its simplicity and flexibility. This paper compares the performance of a set of multicast protocols that use either the traditional timer-based feedback control or a combination of the traditional timers and some representatives in the feedback control. We investigate how the use of representatives and deterministic timers improves feedback control performance.
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.
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.
21336774
An Adapted Lesk Algorithm for Word Sense Disambiguation Using WordNet
This paper presents an adaptation of Lesk's dictionary-based word sense disambiguation algorithm. Rather than using a standard dictionary as the source of glosses for our approach, the lexical database WordNet is employed. This provides a rich hierarchy of semantic relations that our algorithm can exploit. This method is evaluated using the English lexical sample data from the SENSEVAL-2 word sense disambiguation exercise, and attains an overall accuracy of 32%. This represents a significant improvement over the 16% and 23% accuracy attained by variations of the Lesk algorithm used as benchmarks during the Senseval-2 comparative exercise among word sense disambiguation systems.
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.
14498501
A clustering scheme for hierarchical control in multi-hop wireless networks
In this paper we present a clustering scheme to create a hierarchical control structure for multi-hop wireless networks. A cluster is defined as a subset of vertices, whose induced graph is connected. In addition, a cluster is required to obey certain constraints that are useful for management and scalability of the hierarchy. All these constraints cannot be met simultaneously for general graphs, but we show how such a clustering can be obtained for wireless network topologies. Finally, we present an efficient distributed implementation of our clustering algorithm for a set of wireless nodes to create the set of desired clusters.
206575726
Regular multihop logical topologies for lightwave networks
Several government- and industry-funded prototyping and development activities in WDM optical networks are being conducted at various R&D centers. Optical networks can be deployed on top of an existing physical fiber plant that can provide a transparent all-optical signal path to its upper layer, thereby providing broadband services. For instance, an all-optical layer between the physical and ATM layers in a B-ISDN network will significantly improve both efficiency and flexibility for the provision of broadband services. One attractive feature of optical networks is the ease of its logical reconfigurability, i.e., any desired logical network topology can be embedded on top of any given physical fiber plant, subject to the limitations on the number of available wavelengths and transceivers. The logical topologies can be broadly classified into two categories: arbitrary and regular. Nodal connectivity patterns in regular topologies are very systematic and well defined, which simplifies routing and management operations. However, it is difficult to add an arbitrary number of nodes to a regular topology and still maintain its well-defined structure. Over the past few years, several regular logical topologies have been proposed for optical networks. In this article we provide brief descriptions of these regular logical network topologies and a comparative study of their various performance metrics, e.g., average hop distance (viz. network utilization), routing, fault tolerance, and scalability.
16760269
Implementing XML Schema inside a relational database
XML Schema has emerged as a promising data model that unites structured and unstructured content. The Oracle database has led the commercial database community in integrating support for XML Schema inside an enterprise data server. The foundation for this was laid with the absorption of the SQL:1999 'objectrelational' type system in the database, which provided the necessary hierarchical abstractions necessary for representing XML. We look at how XML Schemas have been implemented in Oracle XML DB, what optimizations are available to cover the diverse use-cases for schema-based XML storage and retrieval, and how this technology contributes to richer data management.