Huirong Fu

QoS-driven server migration for Internet data centers

Many organizations have chosen to host Internet applications at Internet data centers (IDCs) located near network access points of the Internet to take advantage of their high availability, large network bandwidths and low network latencies. Current IDCs provide for a dedicated and static allocation of resources to each hosted application. Unfortunately, workloads for these sites are highly variable, leading to poor resource utilization, poor application performance, or both. In this paper, we develop a framework for QoS-driven dynamic resource allocation in IDCs. Termed QuID (quality of service infrastructure on demand), the frameworks contributions are threefold. First, we develop a simple adaptive algorithm to reduce the average number of servers used by an application while satisfying its QoS objectives. Second, we develop an optimal off-line algorithm that bounds the advantage of any dynamic policy and provides a benchmark for performance evaluation. Finally, we perform an extensive simulation study using traces from large-scale E-commerce and search-engine sites. We explore the gains of the QuID algorithms as a function of the system parameters (such as server migration time), algorithm parameters (such as control time scale), and workload characteristics (such as peak-to-mean ratio and autocorrelation function of the request rate).

An IEEE 802.11p-Based Multichannel MAC Scheme With Channel Coordination for Vehicular Ad Hoc Networks

In recent years, governments, standardization bodies, automobile manufacturers, and academia are working together to develop vehicular ad hoc network (VANET)-based communication technologies. VANETs apply multiple channels, i.e., control channel (CCH) and service channels (SCHs), to provide open public road safety services and the improve comfort and efficiency of driving. Based on the latest standard draft IEEE 802.11p and IEEE 1609.4, this paper proposes a variable CCH interval (VCI) multichannel medium access control (MAC) scheme, which can dynamically adjust the length ratio between CCH and SCHs. The scheme also introduces a multichannel coordination mechanism to provide contention-free access of SCHs. Markov modeling is conducted to optimize the intervals based on the traffic condition. Theoretical analysis and simulation results show that the proposed scheme is able to help IEEE 1609.4 MAC significantly enhance the saturated throughput of SCHs and reduce the transmission delay of service packets while maintaining the prioritized transmission of critical safety information on CCH.

Preventing Cooperative Black Hole Attacks in Mobile Ad Hoc Networks: Simulation Implementation and Evaluation

A black hole attack is a severe attack that can be easily employed against routing in mobile ad hoc networks. A black hole is a malicious node that falsely replies for any route requests without having active route to specified destination and drops all the receiving packets. If these malicious nodes work together as a group then the damage will be very serious. This type of attack is called cooperative black hole attack. In S. Ramaswamy et al. (2003), we proposed a solution to identifying and preventing the cooperative black hole attack. Our solution discovers the secure route between source and destination by identifying and isolating cooperative black hole nodes. In this paper, via simulation, we evaluate the proposed solution and compare it with other existing solutions in terms of throughput, packet loss percentage, average end-to-end delay and route request overhead. The experiments show that (1) the AODV greatly suffers from cooperative black holes in terms of throughput and packet losses, and (2) our solution proposed in S. Ramaswamy et al. (2003) presents good performance in terms of better throughput rate and minimum packet loss percentage over other solutions, and (3) our solution can accurately prevent the cooperative black hole attacks. The example findings are: (1) the proposed scheme presents 5 - 8% more communication overhead of route request; and (2) The secure route discovery delay slightly increases the packet loss percentage.

Measuring the performance of IEEE 802.11p using ns-2 simulator for vehicular networks

The 802.11p protocol, also known as wireless access for the vehicular environment (WAVE), has recently gained momentum in the area of research and development. The WAVE protocol provides enhancements to the physical (PHY) and medium access control (MAC) layers of the existing 802.11 wireless standards. These enhancements are required to support the intelligent transportation systems (ITS) initiatives of the US Department of Transportation regarding vehicle-to-vehicle, vehicle-to-infrastructure, and infrastructure-to-vehicle communication. Many research groups have contributed to the development of the protocol. Many of the same individuals have worked to extend the ns-2 network simulator to correctly simulate wireless mobile networking, specifically vehicle adhoc networks (VANETs). The objective of this research project is to measure the performance of the WAVE protocol at the MAC layer, using the ns-2 simulator. Specifically, the simulations measure aggregate throughput, average delay, and packet loss metrics.

An Enhanced Multi-Channel MAC for the IEEE 1609.4 Based Vehicular Ad Hoc Networks

This paper proposes a multi-channel MAC scheme for Vehicular Ad Hoc Networks (VANETs), which dynamically adjusts the intervals of Control Channel (CCH) and Service Channels (SCHs). Markov modeling is conducted to optimize the intervals based on the traffic condition. The scheme also introduces a multi-channel coordination mechanism to provide the contention-free access in SCHs. Theoretical analysis and simulation results show that the proposed scheme is able to help IEEE 1690.4 MAC improve the saturation throughput of SCHs significantly, while maintaining the prioritized transmission of critical safety information on the CCH.

Medium access control in vehicular ad hoc networks

The distinguishing properties of Vehicular Ad hoc wireless Networks (VANETs) strongly challenge the design of Medium Access Control (MAC) protocols, which are responsible for the medium access coordination among active vehicles, as well as the accommodation of both driving safety applications and non-safety applications. In this paper, we focus on a comprehensive survey of VANET MAC schemes by integrating various related issues and challenges. Our analysis not only deepens the understanding of MAC techniques in VANETs but also presents the key ideas and potential directions for future research in this area. In order to significantly improve the communication performance of VANETs, more research efforts on MAC techniques must be made for optimizing multichannel coordination and allocation approaches, enhancing the Quality of Service (QoS) capability, and combating the hidden terminal problem, broadcast storm problem and even ACK (acknowledgment) explosion problem. Copyright

A QoS Supported Multi-Channel MAC for Vehicular Ad Hoc Networks

The emerging wireless vehicular communication technology is intended to improve safety and comfort of transportation systems. Different types of traffic information could be delivered through vehicle-to-vehicle and vehicle-to- infrastructure communications. This paper proposes a Quality-of-Service (QoS) supported multi-channel MAC scheme for Vehicular Ad Hoc Networks (VANETs), which can adaptively tune the contention window for different services at each node, and dynamically adjust the intervals of the Control Channel (CCH) and the Service Channels (SCHs) working in multi-rate. Theoretical model is proposed to obtain the contention window and optimize the intervals based on traffic conditions. Analysis and simulation results show that the proposed MAC is able to help IEEE 1690.4 MAC support QoS services, while ensuring the high saturation throughput and the prioritized transmission of critical safety information.

On privacy in time series data mining

Traditional research on preserving privacy in data mining focuses on time-invariant privacy issues. With the emergence of time series data mining, traditional snapshot-based privacy issues need to be extended to be multi-dimensional with the addition of time dimension. We find current techniques to preserve privacy in data mining are not effective in preserving time-domain privacy. We present data flow separation attack on privacy in time series data mining, which is based on blind source separation techniques from statistical signal processing. Our experiments with real data show that this attack is effective. By combining the data flow separation method and the frequency matching method, an attacker can identify data sources and compromise time-domain privacy. We propose possible countermeasures to the data flow separation attack in the paper.

A Novel Location-Service Protocol Based on

This paper presents a novel k-hop cluster-based location service (KCLS) protocol in mobile ad hoc networks, which is able to well balance the tradeoff between the communication overheads and the accuracy of location information. Other advantages of the proposed KCLS protocol include excellent network scalability and tolerance of link breakage that can significantly reduce communication overheads and the latency caused by route path recovery. The numerical results obtained from both theoretical analysis and simulations have shown that the cost of location management using the KCLS protocol is less than 2% of the location-management cost using the link-state protocol. Especially for a large value of k, the proposed KCLS protocol is not only able to suppress the increasing rate of the total cost when the number of hosts in the network increases but also increases the hit probability of location service and reduces the passive effect of host mobility on control overhead as well. With good scalability and the capability of self-discovery, the proposed KCLS protocol is adaptable to accommodate most applications in ad hoc networks

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This paper focuses on the optimization of network bandwidth allocation and buffer dimensioning to transport pre-stored MPEG video data from source to playback destination across ATM networks. This is one of the most important issues in the support of video-on-demand (VoD) service. This paper provides a novel scheme in the dynamic allocation of bandwidth to segments of video using ABR mode. The dynamic bandwidth allocation is based on a new concept, called playback tunnel which is obtained from the traffic characteristics of the pre-stored MPEG video trace to determine the optimum of transmission bandwidth as well as the buffer capacity to ensure that the playback buffer neither underflows nor overflows. The proposed scheme is tested with real-life MPEG video traces. The obtained results have shown its significant performance improvement in terms of the capacity of playback buffer, the start-up playback delay, the size of video segment and the network multiplexing gain.