In this paper, we study the quality-of-service (QoS)-aware replica placement problem in grid environments. Although there has been much work on the replica placement problem in parallel and distributed systems, most of them concern average system performance and have not addressed the important issue of quality of service requirement. In the very few existing work that takes QoS into consideration, a simplified replication model is assumed; therefore, their solution may not be applicable to real systems. In this paper, we propose a more realistic model for replica placement, which consider storage cost, update cost, and access cost of data replication, and also assumes that the capacity of each replica server is bounded.The QoS-aware replica placement is NP-complete even in the simple model. We propose two heuristic algorithms, called greedy remove and greedy add to approximate the optimal solution. Our extensive experiment results demonstrate that both greedy remove and greedy add find a near-optimal solution effectively and efficiently. Our algorithms can also adapt to various parallel and distributed environments.

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Many multimedia applications require guaranteed Quality of Service(QoS) in communication networks. Typically, the QoS includes bandwidth, delay, and delay jittel: This paper presents a real-time protocol to support multimedia communications in which the connections are established with eflcient resource reservation and proper admission control. During data transmission, the rate, jitter control, and packet scheduling techniques are employed to fulfill the pegormanee contract. The protocol also incorporates multicast function to provide group communications. This protocol is implemented on a high-speed network which consists of interconnected ATM switches, FDDI networks, routers, and hosts. Experiments have been carried out to evaluate the effectiveness of the QoS guaranteedprotocol. Measured results indicate that the proposed protocol peflorms well to guarantee the QoS in terms of bandwidth, delay, and delay jittel:The improvement in communication technology has made it possible to provide multimedia applications over high speed networks. Video, audio, and image are the primary media in multimedia applications, such as video on demand(VOD), distance learning, and video conference. To have better representation of these information, it is necessary to ensure some performance parameters, such as bandwidth, delay, delay jitter, and loss rate, on transmission networks. ATM, FDDI, and 100VG-AnyLAN are the typical network architectures that offer guaranteed performance '