5173801
Load Balance Algorithms for Anycast
Increasingly, replicated anycast servers are being used to deliver network applications and service ever increasing user requests. Therefore, the strategies used to guarantee network bandwidth prerequisites and perform load balancing across the nodes of an anycast group are critical to the performance of online applications. In this paper, we model user requests, network congestion and latency, and server load using a combination of hydro-dynamics and queuing theory to develop an efficient job distribution strategy. Current, anycast research does not explicitly consider the system load of nodes within an anycast groups when distributing requests. Therefore, the performance of a heavily loaded anycast system can quickly become congested and uneven as jobs are routed to closely linked nodes which are already saturated with requests. In comparison, the nodes of further away systems remain relatively unused because of other issues such as network bandwidth and latency during these times. Our system redirects requests from busy systems to the idle, remotely linked nodes, to process requests faster in spite of slower network access. Using an empirical study, we show this technique can improve request performance, and throughput with minimal network probing overhead.
42192006
Reducing the Bandwidth Requirements of P2P Keyword Indexing
This paper describes the design and evaluation of a federated, peer-to-peer indexing system, which can be used to integrate the resources of local systems into a globally addressable index using a distributed hash table. The salient feature of the indexing systems design is the efficient dissemination of term-document indices using a combination of duplicate elimination, leaf set forwarding and conventional techniques such as aggressive index pruning, index compression, and batching. Together these indexing strategies help to reduce the number of RPC operations required to locate the nodes responsible for a section of the index, as well as the bandwidth utilization and the latency of the indexing service. Using empirical observation we evaluate the performance benefits of these cumulative optimizations and show that these design trade-offs can significantly improve indexing performance when using a distributed hash table.
184418
Self-adaptive clock synchronization for computational grid
This paper presents an innovative method to synchronize physical clocks for a computational grid, in particular for a computational grid linked through the asynchronous Intranet or Internet environments. The method discussed is an asynchronous self-adaptive clock synchronization mechanism. Two strategies for clock synchronisationare introduced. (1), Use continuous time intervals to calculate the precision of clocks, which can reduce the effect of network delay efficiently. (2) Every node synchronizes its clock, with its leader actively. In addition, a node self-adaptive model is presented, and the relationship between the clock precision and synchronization time is induced, hence a node can predict when it should begin the synchronization process. Detailed simulation and extension of this issue are provided at the end of the paper. The presented model is both practical and feasible.
10404783
Spam Filtering based on Preference Ranking
When the average number of spam messages received is continually increasing exponentially, both the Internet service provider and the end user suffer. The lack of an efficient solution may threaten the usability of the email as a communication means. In this paper we present a filtering mechanism applying the idea of preference ranking. This filtering mechanism will distinguish spam emails from other email on the Internet. The preference ranking gives the similarity values for nominated emails and spam emails specified by users, so that the ISP/end users can deal with spam emails at filtering points. We designed three filtering points to classify nominated emails into spam email, unsure email and legitimate email. This filtering mechanism can be applied on both middleware and at the client-side. The experiments show that high precision, recall and TCR (total cost ratio) of spam emails can be predicted for the preference based filtering mechanisms
17859913
Security in the online e-learning environment
This paper addresses the role of security in the collaborative e-learning environment, and in particular, the social aspects of security and the importance of identity. It represents a case study, completed in Nov 2004, which was conducted to test the sense of security that students experienced whilst using the wiki platform as a means of online collaboration in the tertiary education environment. Wikis, fully editable Web sites, are easily accessible, require no software and allow its contributors (in this case students) to feel a sense of responsibility and ownership. A comparison between two wiki studies will be made whereby one group employed user login and the other maintained anonymity throughout the course of the study. The results consider the democratic participation and evolution of the work requirements over time, which in fact ascertains the nonvalidity of administrative identification.
12866276
A Load Balancing Algorithm for Web Based Server Grids
Load balance is a critical issue in distributed systems, such as server grids. In this paper, we propose a Balanced Load Queue (BLQ) model, which combines the queuing theory and hydro-dynamic theory, to model load balance in server grids. Base on the BLQ model, we claim that if the system is in the state of global fairness, then the performance of the whole system is the best. We propose a load balanced algorithm based on the model: the algorithm tries its best to keep the system in the global fairness status using job deviation. We present three strategies: best node, best neighbour, and random selection, for job deviation. A number of experiments are conducted for the comparison of the three strategies, and the results show that the best neighbour strategy is the best among the proposed strategies. Furthermore, the proposed algorithm with best neighbour strategy is better than the traditional round robin algorithm in term of processing delay, and the proposed algorithm needs very limited system information and is robust.
16218050
A tool for constructing service replication systems
Service replication as a key to providing high availability, fault tolerance and good performance in distributed systems. However, building a service replication system is a difficult and complex task. This paper describes a tool that mimics the design of the remote procedure call (RPC) system to support building distributed service replication systems. The tool includes an interface definition language for describing a replica group, a language preprocessor and a runtime library system.
2813000
Detecting and tolerating failures in a loosely integrated heterogeneous database system
This article presents the design and prototype implementation of a fault detection and fault tolerance facility based on the reactive system model for a loosely integrated heterogeneous database system running on a network of workstations. The database system consists of a number of fully autonomous databases that, through their willingness, can share some portion of their information. Sensors (functions that expose some part of the state of an object) are placed on individual databases and system objects (such as traders, agents, and other sensors). Other databases and system objects, and applications can subscribe to a sensor and therefore are notified whenever the sensor value changes. The fault detection mechanism uses sensors to monitor individual databases and system objects and to detect database or system faults. The fault tolerance mechanism uses actuators (functions that can change the state of an object) to react on database or system faults.
1954273
An architecture for building reliable distributed object-based systems
This paper proposes an architecture for designing fault-tolerant distributed object systems. The proposed architecture attempts to bring advances in client-server, remote procedure call, reliable group communication, and object orientation technologies under a unified architecture to ease application developers' work of building reliable distributed systems. The resulting application systems should be enhanced with modularity and flexibility.
17849791
A tool for layered analysing and understanding of distributed programs
Distributed programs are harder to analyse and understand than sequential programs for a number of reasons. First, a distributed program consists of many entities at different levels of abstraction. Second, communication among the entities of a distributed program may happen concurrently and nondeterministically. To be able to analyse these entities and the communication events among them is therefore essential for understanding any distributed program. This paper describes a tool for assisting the analysis and understanding of distributed programs. The tool analyses the entities and communication events of a distributed program at four levels of abstraction. At the highest level, the tool displays the communication relationships between programs (e.g. server and client programs). At the second level, the communication between processes is displayed. At the third level, the communication between events is displayed. The fourth level is the lowest: it uses a text editor to show the relevant statements that carry out the communication. The tool has been used in the teaching of courses related to distributed computing since 1993.
33519597
A system for managing remote procedure call transactions
Abstract This paper describes the design and implementation of a remote procedure call (RFC) transaction manager. The structures and constructions of RFC-based systems have been widely discussed, yet how to manage the RFC transactions by using these existing structures and constructions remains unclear. We have designed a system for managing RFC transactions based on our RFC transaction model. The system is designed at first to manage single RFC transactions. It is then expanded to manage parallel RFC transactions as well. Some properties of the system are described. We also present some descriptions of the preliminary implementation of our RFC transaction manager.