Ge-Ming Chiu

The odd-even turn model for adaptive routing

This paper presents a model for designing adaptive wormhole routing algorithms for meshes without virtual channels. The model restricts the locations where some turns can be taken so that deadlock is avoided. In comparison with previous methods, the degree of routing adaptiveness provided by the model is more even for different source-destination pairs. The mesh network may benefit from this feature in terms of communication efficiency. Simulation results show that the even adaptiveness provided by the odd-even turn model makes message routing less vulnerable to nonuniform factors such as hot spot traffic. In addition, this property results in a smaller fluctuation of the network performance with respect to different traffic patterns.

A fault-tolerant routing strategy in hypercube multicomputers

We investigate fault-tolerant routing which aims at finding feasible minimum paths in a faulty hypercube. The concept of unsafe node and its extension are used in our scheme. A set of stringent criteria is proposed to identify the possibly bad candidates for forwarding a message. As a result, the number of such undesirable nodes is reduced without sacrificing the functionality of the mechanism. Furthermore, the notion of degree of unsafeness for classifying the unsafe nodes is introduced to facilitate the design of efficient routing algorithms which rely on having each node keep the states of its nearest neighbors. We show that a feasible path of length no more than the Hamming distance between the source and the destination plus four can always be established by the routing algorithm as long as the hypercube is not fully unsafe. The issue of deadlock freeness is also addressed in this research. More importantly, another fault-tolerant routing algorithm, which requires only a constant of five virtual networks in wormhole routing to ensure the property of deadlock freeness for a hypercube of any size, is presented in this paper.

A fault-tolerant routing scheme for meshes with nonconvex faults

In this paper, we propose a fault-tolerant routing scheme for meshes with solid faults. A Rag bit is introduced for guiding misrouted messages. By fully utilizing virtual channels of each class, our algorithm uses only three virtual channels to ensure the property of deadlock freeness. Our scheme is able to handle solid faults whose associated fault rings overlap. In addition, the proposed algorithm can be used to route messages when fault regions touch the boundaries of the mesh.

An efficient submesh allocation scheme for two-dimensional meshes with little overhead

This paper presents a submesh allocation scheme for two-dimensional mesh systems. The submesh detection process considers only those available free submeshes that border from the left on some allocated submeshes or have their left boundaries aligned with that of the mesh. Fragmentation in the system can be reduced as a result. More importantly, we present an efficient approach to facilitate the detection of such available submeshes. The basic idea of the approach is to place the allocated submeshes of the busy set in a certain order so as to reduce the complexity of subtraction operations required for submesh detection. The method is simple and causes an amount of overhead which is only a fraction of that produced by previous algorithms. Extensive simulation has been conducted to evaluate the performance of the proposed scheme. The results show that when allocation overhead is considered, the proposed scheme may outperform previous methods.

Use of routing capability for fault-tolerant routing in hypercube multicomputers

The concept of routing capability is proposed to assist fault-tolerant routing in hypercubes. Routing capability is defined with respect to the entire spectrum of distance. As a result, the amount of information that is useful for message routing is increased. An algorithm is presented to facilitate efficient fault-tolerant routing of messages. The algorithm routes a message in an attempt to minimize derouting. Furthermore, the concept of directed routing capability which contains more useful information for fault-tolerant routing is introduced. Simulation results demonstrate the usefulness of our approach.

A new quorum-based scheme for managing replicated data in distributed systems

We propose a new quorum-based scheme for managing replicated data in distributed systems. We first introduce a concept called difference pair to establish the basics for cyclic read-write coteries. A simple and efficient model is then presented to facilitate the construction of read-write coteries. The read-write coteries generated by the model are strictly symmetric. Our model can be applied to an arbitrary number of copy sites. More importantly, by introducing a parameter in the construction model, our scheme offers the flexibility of adjusting the sizes of read and write quorums. Such flexibility allows read and write quorums to be readily tailored for each individual data item according to its own request demand. Enhancement of data availability is also addressed by our model.

Efficient rollback-recovery technique in distributed computing systems

We propose an approach for implementing rollback recovery in a distributed computing system. A concept of logical ring is introduced for the maintenance of information required for consistent recovery from a system crash. Message processing order of a process is kept by all other processes on its logical ring. Transmission of data messages are accompanied by the circulation of the associated order messages on the ring. The sizes of the order messages are small. In addition, redundant transmission of order information is avoided, thereby reducing the communication overhead incurred during failure free operation. Furthermore, updating of the order information and garbage collection task are simplified in the proposed mechanism. Our approach does not require information about message processing order be written to stable storage; in fact, the time consuming operations of saving information in stable storage are confined to the checkpointing activities. When failures occur, a surviving process need roll back only if some preceding order information is totally lost, which is relatively unlikely considering the ever growing speed of communication networks. It is shown that a system can recover correctly as long as there exists at least one surviving process.

Fault-tolerant routing strategy using routing capability in hypercube multicomputers

This paper addresses fault-tolerant routing which is concerned with finding feasible minimum paths in a faulty hypercube. The concept of routing capability, which is defined with respect to the entire spectrum of distance, is proposed to assist routing function. The amount of information that is useful for message routing is increased with our scheme. The proposed algorithm routes a message in an attempt to minimize derouting. In particular, it makes use of the information embedded in routing capabilities to establish a path for a message for which an upper bound on its length may be determined at the source. We then propose the notion of directed routing capability which captures more useful information for shortest path routing in comparison with undirected counterpart. Routing in hypercubes with link failures is also addressed.

Close Dominance Graph: An Efficient Framework for Answering Continuous Top-k Dominating Queries

There are two preference-based queries commonly used in database systems: (1) top-k query and (2) skyline query. By combining the ranking rule used in top-\(k\) query and the notion of dominance relationships utilized in the skyline query, a top-\(k\) dominating query emerges, providing a new perspective on data processing. This query returns the \(k\) records with the highest domination scores from the dataset. However, the processing of the top-\(k\) dominating query is complex when the dataset operates under a streaming model. With new data being continuously generated while stale data being removed from the database, a continuous top-\(k\) dominating query (cTKDQ) requires that updated results can be returned to users at any time. This work explores the cTKDQ problem and proposes a unique indexing structure, called a Close Dominance Graph (CDG), to support the processing of a cTKDQ. The CDG provides comprehensive information regarding the dominance relationship between records, which is vital in answering a cTKDQ with a limited search space. The update process for a cTKDQ is then converted to a simple update affecting a small portion of the CDG. Experimental results show that this scheme is able to offer much better performance when compared with existing solutions.

An efficient scheduling algorithm for scalable video streaming over P2P networks

Abstract During recent years, the Internet has witnessed rapid advancement in peer-to-peer (P2P) media streaming. In these applications, an important issue has been the block scheduling problem, which deals with how each node requests the media data blocks from its neighbors. In most streaming systems, peers are likely to have heterogeneous upload/download bandwidths, leading to the fact that different peers probably perceive different streaming quality. Layered (or scalable) streaming in P2P networks has recently been proposed to address the heterogeneity of the network environment. In this paper, we propose a novel block scheduling scheme that is aimed to address the P2P layered video streaming. We define a soft priority function for each block to be requested by a node in accordance with the block’s significance for video playback. The priority function is unique in that it strikes good balance between different factors, which makes the priority of a block well represent the relative importance of the block over a wide variation of block size between different layers. The block scheduling problem is then transformed to an optimization problem that maximizes the priority sum of the delivered video blocks. We develop both centralized and distributed scheduling algorithms for the problem. Simulation of two popular scalability types has been conducted to evaluate the performance of the algorithms. The simulation results show that the proposed algorithm is effective in terms of bandwidth utilization and video quality.