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.
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.
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.
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.
12036050
A Dynamic Manifestation Approach for Providing Universal Access to Digital Library Objects
Digital libraries are concerned with the creation and management of information sources, the movement of information across global networks, and the effective use of this information by a wide range of users. A digital library is a vast collection of objects that are of multimedia nature, e.g. text, video, images, and audio. Users wishing to access the digital library objects may possess varying capabilities, preferences, domain expertise, and may use different information appliances. Facilitating access to complex multimedia digital library objects that suits the users' requirements is known as universal access. We present an object manifestation approach in which digital library objects automatically manifest themselves to cater to the users' capabilities and characteristics. We provide a formal framework, based on Petri nets, to represent the various components of the digital library objects, their modality and fidelity, and the playback synchronization relationships among them. We develop methodologies for object delivery without any deadtime under network delays.
8594061
Data sharing and recovery in gigabit-networked databases
Major advances in optical fiber transmission and switching technology have enabled the development of very high speed networks with data rates of the order of gigabits per second. It is anticipated that in the future, wide area gigabit networks will interconnect database servers around the globe creating extremely powerful distributed information systems. In this paper, we examine the implications of such a high speed network on data access and sharing techniques and propose a lock-based concurrency control protocol and a log-based recovery protocol that ensures data consistency in gigabit-networked databases. Both protocols exploit the characteristics of a gigabit network to enhance the performance of the database system and, in particular, the fact that the size of the message is less of a concern than the number of sequential phases of message passing.
17465088
An efficient channel-feedback-based adaptive protocol for scheduling variable-length messages on slotted, high-speed fiber optic LANs/MANs
This paper is based on the continuation-bit approach in conjunction with a probabilistic scheduling strategy called the p/sub i/-persistent protocol. This combination has been proposed as an efficient multiple access protocol for transmitting variable-length messages on slotted, high-speed, fiber-optic, bus-structured local and metropolitan area networks (LANs/MANs). Specifically, the authors extend the previous static model on this approach to the dynamic case so that the protocol can be implemented. A dynamic simulation model of the protocol using the continuation-bit approach has been formulated, and channel feedback information has been used to calibrate the operating parameters in real time. Since the goal was to study the operation of the dynamic protocol with variable-length messages, variable-bit-rate coded (i.e., compressed) video was chosen as the traffic to be carried by the network in the illustrative examples. The simulation model indicates that channel feedback is a good approach for dynamically adjusting the network parameters as the network loading and the message lengths fluctuate. Even at a network utilization of 0.6, it was found that almost all video messages were transmitted from the station buffers before the next video message arrived.<<ETX>>
2137839
Implementation of a Scalable Context-Aware Computing System
Context-aware computing involves the automatic tailoring of information and services based on the current location of the user. In this paper, we describe our experience in implementing Rover, a system that enables location-based services, as well as the traditional time-aware, user-aware and device-aware services. To achieve system scalability to very large client sets, Rover servers are implemented in an “action-based” concurrent software architecture that enables fine-grained application-specific scheduling of tasks. We have demonstrated its feasibility through implementations for both outdoor and indoor environments on multiple platforms.
1432948
Exploiting diversity to enhance multimedia streaming over cellular links
Wireless wide area networks (WWANs) are becoming ubiquitous across most geographic regions, enabling simultaneous coverage from multiple providers. WWAN channels exhibit both uncorrelated and correlated behaviour on a variety of levels. In this paper we examine the statistical properties of WWAN links, and illustrate the benefits in heterogeneity that can be exploited to improve statistical throughput and multimedia quality. Our results are based on real network measurements. We describe the design and implementation of a high quality multimedia streaming application that implements WWAN streaming optimisations utilising unequal error protection coding techniques, and we evaluate the performance over an operational WWAN network.
43624883
Algorithms for optimized node arrangements in ShuffleNet based multihop lightwave networks
The unique capabilities of lightwave technology are exploited in order to construct optimized regular multihop networks when the traffic flow among the network nodes is asymmetric. The specific problem addressed is as follows: given that the network nodes must be connected in a regular interconnection pattern and that the node positions in the regular network can be adjusted by properly tuning their (optical) transceivers, what is the best node placement in a given regular topology? In particular, the ShuffleNet-based regular topology is examined. ShuffleNet has the property of producing large connected graphs with small degree and diameter. In order words, it can interconnect a large number of nodes with a small number of transceivers per node such that information from a source can reach its destination in a small number of hops. Since finding the optimal node placement is a computationally hard problem, efficient heuristic algorithms are formulated to design optimized ShuffleNet structures for a given traffic matrix.<<ETX>>
222765
Minimum energy paths for reliable communication in multi-hop wireless networks
Current algorithms for minimum-energy routing in wireless networks typically select minimum-cost multi-hop paths. In scenarios where the transmission power is fixed, each link has the same cost and the minimum-hop path is selected. In situations where the transmission power can be varied with the distance of the link, the link cost is higher for longer hops; the energy-aware routing algorithms select a path with a large number of small-distance hops. In this paper, we argue that such a formulation based solely on the energy spent in a single transmission is misleading --- the proper metric should include the total energy (including that expended for any retransmissions necessary) spent in reliably delivering the packet to its final destination.We first study how link error rates affect this retransmission-aware metric, and how it leads to an efficient choice between a path with a large number of short-distance hops and another with a smaller number of large-distance hops. Such studies motivate the definition of a link cost that is a function of both the energy required for a single transmission attempt across the link and the link error rate. This cost function captures the cumulative energy expended in reliable data transfer, for both reliable and unreliable link layers. Finally, through detailed simulations, we show that our schemes can lead to upto 30-70% energy savings over best known current schemes, under realistic environments.