Jenn-Wei Lin

QoS-Aware Data Replication for Data-Intensive Applications in Cloud Computing Systems

Cloud computing provides scalable computing and storage resources. More and more data-intensive applications are developed in this computing environment. Different applications have different quality-of-service (QoS) requirements. To continuously support the QoS requirement of an application after data corruption, we propose two QoS-aware data replication (QADR) algorithms in cloud computing systems. The first algorithm adopts the intuitive idea of high-QoS first-replication (HQFR) to perform data replication. However, this greedy algorithm cannot minimize the data replication cost and the number of QoS-violated data replicas. To achieve these two minimum objectives, the second algorithm transforms the QADR problem into the well-known minimum-cost maximum-flow (MCMF) problem. By applying the existing MCMF algorithm to solve the QADR problem, the second algorithm can produce the optimal solution to the QADR problem in polynomial time, but it takes more computational time than the first algorithm. Moreover, it is known that a cloud computing system usually has a large number of nodes. We also propose node combination techniques to reduce the possibly large data replication time. Finally, simulation experiments are performed to demonstrate the effectiveness of the proposed algorithms in the data replication and recovery.

An efficient fault-tolerant approach for Mobile IP in wireless systems

This paper presents the fault tolerance of Mobile IP in wireless systems. Mobile IP can support wireless users with continuous network connections while changing locations. It is achieved by allocating a number of mobility agents (foreign agents and home agents) in the architecture of a wireless system. If a failure occurs in a mobility agent, the wireless users located in the coverage area of the faulty mobility agent will lose their network connections. To tolerate the failures of mobility agents, this paper proposes an efficient approach to maintaining the network connections of wireless users without being affected by the failures. Once detecting a failure in a mobility agent, failure-free mobility agents are dynamically selected to be organized as a backup set to take over the faulty mobility agent. Compared to the previous approaches, the proposed approach does not take any actions against failures during the failure-free period. Besides, the hardware redundancy technique is also not used in the proposed approach. The overhead of the proposed approach is analyzed using the M/G/c/c queuing model. The results show that the proposed approach can effectively resolve the fault-tolerant problem of Mobile IP in wireless systems.

Improving the coverage of randomized scheduling in wireless sensor networks

Randomized scheduling is a well-known scheduling algorithm for wireless sensor networks to prolong network lifetime. In this algorithm, sensor nodes are randomly assigned to multiple working subsets. These subsets alternatively perform the sensing tasks for monitoring a sensor filed. In each subset, only a portion of sensor nodes are active. It is difficult to maintain the full sensing coverage and network connectivity in a sensor field. For the network connectivity problem of the randomized scheduling, it has been discussed. In this paper, we propose a distributed approach for assisting the randomized scheduling to provide the full coverage. To efficiently achieve this goal, the proposed approach is divided into two main stages: field partition and coverage improvement. The handling problems of these two stages can be transferred to two geometry problems: Voronoi polygon construction and circle covering. Simulation results show that the proposed approach can significantly improve the coverage quality of the randomized scheduling.

Fault Tolerance for Super-Peers of P2P Systems

This paper presents an efficient fault-tolerant approach for the super-peers of peer-to-peer (P2P) file sharing systems. In the super-peer based P2P file sharing system, peers are organized into multiple groups. In each group, it has a special peer called super peer to serve the regular peers within the group. In this hierarchical architecture, if the super peer departs (fails), any file queries to its serving regular peers cannot be delivered. In the proposed approach, we propose a multiple publication technique to make each regular peer logically connect with two or more super peers in other groups. If a regular peer finds that its serving super peer cannot work, one of its other connected super peers will be selected as its new serving super peer to continuously process the file queries. To examine the effectiveness of the proposed approach, comprehensive simulations are performed to quantify the performance and overhead of the proposed approach.Several recent studies identify the memory system as the most frequent source of hardware failures in commercial servers. Techniques to protect the memory system from failures must continue to service memory requests, despite hardware failures. Furthermore, to support existing OSs, the physical address space must be retained following reconfiguration. Existing techniques either suffer from a high performance overhead or require pervasive hardware changes to support transparent recovery. In this paper, we propose physical address indirection (PAI), a lightweight, hardware-based mechanism for memory system failure recovery. PAI provides a simple hardware mapping to transparently reconstruct affected data in alternate locations, while maintaining high performance and avoiding physical address changes. With full-system simulation of commercial and scientific workloads on a 16-node distributed shared memory server, we show that prior techniques have an average degraded mode performance loss of 14 % and 51 % for commercial and scientific workloads, respectively. Using PAIs data- swap reconstruction, the same workloads have 1 % and 32 % average performance losses.

A weight-aware channel assignment algorithm for mobile multicast in wireless mesh networks

Abstract Wireless mesh networks (WMNs) are one of key technologies for next generation wireless networks. In this paper, we propose a heuristic channel assignment algorithm with weight awareness to support mobile multicast in WMNs. To enhance network throughput, our algorithm is based on the path forwarding weight to perform channel assignment. In addition to non-overlapping channels, partially-overlapping channels are also used in channel assignment. To fully exploit all available channels in channel assignment, we devise a new channel selection metric to consider the channel separation and the distance between nodes. In mobile multicast, the multicast tree structure cannot be fixed due to receiver (multicast member) mobility. The change of the multicast tree structure will result in channel re-assignment. The proposed algorithm is based on a critical-event driven manner to reduce the times of channel re-assignment as much as possible. Finally, we perform simulation experiments to show the effectiveness of the proposed channel assignment algorithm.

A delay-constrained and priority-aware channel assignment algorithm for efficient multicast in wireless mesh networks

Many popular applications of wireless mesh networks (WMNs) depend on delay-constraint multicast communication. To support such multicast communication, this paper proposes a distributed and polynomial-time heuristic channel assignment algorithm for WMNs. The proposed algorithm considers that the multicast session requests arrive dynamically and have different priorities. When a delay-constrained multicast session is issued, the multicast tree corresponding to the session is first established. The proposed algorithm divides the path delay constraint of the multicast tree into a number of the node-based delay constraints. This algorithm also devises multiple channel selection criteria to exploit all available channels of the WMN. Using these selection criteria, each node on the multicast tree can select the best channel to meet its node delay constraint and minimize the total interference for all existing multicast sessions. In the interference minimization, the priority factor is taken into account to prevent high-priority multicast sessions from incurring more interference than low-priority multicast sessions. Finally, this paper performs simulations to demonstrate the effectiveness of the proposed heuristic channel assignment algorithm through comparison with the optimal solution.

Redirection based recovery for MPLS network systems

To provide a reliable backbone network, fault tolerance should be considered in the network design. For a multiprotocol label switching (MPLS) based backbone network, the fault-tolerant issue focuses on how to protect the traffic of a label switched paths (LSP) against node and link failures. In IETF, two well-known recovery mechanisms (protection switching and rerouting) have been proposed. To further enhance the fault-tolerant performance of the two recovery mechanisms, the proposed approach utilizes the failure-free LSPs to transmit the traffic of the failed LSP (the affected traffic). To avoid affecting the original traffic of each failure-free LSP, the proposed approach applies the solution of the minimum cost flow to determine the amount of affected traffic to be transmitted by each failure-free LSP. For transmitting the affected traffic along a failure-free working LSP, IP tunneling technique is used. We also propose a permission token scheme to solve the packet disorder problem. Finally, simulation experiments are performed to show the effectiveness of the proposed approach.

On characteristics of DEF communication-induced checkpointing protocols

Domino-Effect Freedom (DEF) is a property stating that unbounded, cascading rollback propagation will not occur during the process of finding a consistent global checkpoint. DEF checkpointing protocols can be classified into two different categories: index-based and model-based. An index-based protocol timestamps local checkpoints with sequence numbers for achieving consistency, while a model-based one prohibits the formation of particular checkpoint and communication patterns in the execution. We explore several characteristics of communication-induced checkpointing protocols with the DEF property. First, we demonstrate that there is no optimal online scalar DEF protocol, in terms of the number of forced checkpoints. Then some techniques for comparing protocols are proposed. We construct some patterns or give formal proofs to compare the performance of both index-based and model-based protocols.

Fault-tolerant design for wide-area Mobile IPv6 networks

Mobile IPv6 provides the mobility management for IPv6 protocol. To establish a reliable Mobile IPv6 network, fault tolerance should be also considered in the network design. This paper presents an efficient fault-tolerant approach for Mobile IPv6 networks. In the proposed approach, if a failure is detected in the home agent (HA) of a mobile node, a preferable survival HA is selected to continuously serve the mobile node. The preferable survival HA is the HA that does not incur failure and is neighboring the current location of the mobile node. The proposed approach is based on the preference of each mobile node to achieve the fault tolerance of the HA. Finally, we perform simulations to evaluate the performance of the proposed approach.

On the fully-informed communication-induced checkpointing protocol

Communication-induced checkpointing (CIC) protocols can be used to prevent the domino effect. The fully-informed (FI) protocol proposed in the literature is known as the best CIC protocol so far. In this paper, we investigate some properties of such a protocol. First, we discover that an enhancement adopted by the FI protocol rarely takes effect in practice. In particular, we prove that such an enhancement is invalid over a tree communication network. Moreover, the size of the control information that the FI protocol piggybacks on application messages can be further reduced on such a type of network. Next, we show how to apply the FI protocol to another improved indexing strategy introduced in the literature. The management of a Boolean array in its control information carried on a message must be modified. Finally, we present a simulation study to analyze the properties of the FI protocol.