Manoj Misra

On the Design of Adaptive and Decentralized Load Balancing Algorithms with Load Estimation for Computational Grid Environments

In this paper, we address several issues that are imperative to grid environments such as handling resource heterogeneity and sharing, communication latency, job migration from one site to other, and load balancing. We address these issues by proposing two job migration algorithms, which are MELISA (modified ELISA) and LBA (load balancing on arrival). The algorithms differ in the way load balancing is carried out and is shown to be efficient in minimizing the response time on large and small-scale heterogeneous grid environments, respectively. MELISA, which is applicable to large-scale systems (that is, interGrid), is a modified version of ELISA in which we consider the job migration cost, resource heterogeneity, and network heterogeneity when load balancing is considered. The LBA algorithm, which is applicable to small-scale systems (that is, intraGrid), performs load balancing by estimating the expected finish time of a job on buddy processors on each job arrival. Both algorithms estimate system parameters such as the job arrival rate, CPU processing rate, and load on the processor and balance the load by migrating jobs to buddy processors by taking into account the job transfer cost, resource heterogeneity, and network heterogeneity. We quantify the performance of our algorithms using several influencing parameters such as the job size, data transfer rate, status exchange period, and migration limit, and we discuss the implications of the performance and choice of our approaches.

Cooperative Caching Strategy in Mobile Ad Hoc Networks Based on Clusters

In this paper, we present a scheme, called Cluster Cooperative (CC) for caching in mobile ad hoc networks. In CC scheme, the network topology is partitioned into non-overlapping clusters based on the physical network proximity. For a local cache miss, each client looks for data item in the cluster. If no client inside the cluster has cached the requested item, the request is forwarded to the next client on the routing path towards server. A cache replacement policy, called Least Utility Value with Migration (LUV-Mi) is developed. The LUV-Mi policy is suitable for cooperation in clustered ad hoc environment because it considers the performance of an entire cluster along with the performance of local client. Simulation experiments show that CC caching mechanism achieves significant improvements in cache hit ratio and average query latency in comparison with other caching strategies.

Distributed real time database systems: background and literature review

Today’s real-time systems (RTS) are characterized by managing large volumes of dispersed data making real-time distributed data processing a reality. Large business houses need to do distributed processing for many reasons, and they often must do it in order to stay competitive. So, efficient database management algorithms and protocols for accessing and manipulating data are required to satisfy timing constraints of supported applications. Therefore, new research in distributed real-time database systems (DRTDBS) is needed to investigate possible ways of applying database systems technology to real-time systems. This paper first discusses the performance issues that are important to DRTDBS, and then surveys the research that has been done so far on the issues like priority assignment policy, commit protocols and optimizing the use of memory in non-replicated/replicated environment pertaining to distributed real time transaction processing. In fact, this study provides a foundation for addressing performance issues important for the management of very large real time data and pointer to other publications in journals and conference proceedings for further investigation of unanswered research questions.

Cooperative caching in mobile ad hoc networks based on data utility

Cooperative caching, which allows sharing and coordination of cached data among clients, is a potential technique to improve the data access performance and availability in mobile ad hoc networks. However, variable data sizes, frequent data updates, limited client resources, insufficient wireless bandwidth and clients mobility make cache management a challenge. In this paper, we propose a utility based cache replacement policy, least utility value (LUV), to improve the data availability and reduce the local cache miss ratio. LUV considers several factors that affect cache performance, namely access probability, distance between the requester and data source/cache, coherency and data size. A cooperative cache management strategy, Zone Cooperative (ZC), is developed that employs LUV as replacement policy. In ZC one-hop neighbors of a client form a cooperation zone since the cost for communication with them is low both in terms of energy consumption and message exchange. Simulation experiments have been conducted to evaluate the performance of LUV based ZC caching strategy. The simulation results show that, LUV replacement policy substantially outperforms the LRU policy.

Distributed Denial of Service Prevention Techniques

The significance of the DDoS problem and the increased occurrence, sophistication and strength of attacks has led to the dawn of numerous prevention mechanisms. Each proposed prevention mechanism has some unique advantages and disadvantages over the others. In this paper, we present a classification of available mechanisms that are proposed in literature on preventing Internet services from possible DDoS attacks and discuss the strengths and weaknesses of each mechanism. This provides better understanding of the problem and enables a security administrator to effectively equip his arsenal with proper prevention mechanisms for fighting against DDoS threat.

Defending against Distributed Denial of Service Attacks: Issues and Challenges

ABSTRACT Distributed Denial of Service (DDoS) attacks on user machines, organizations, and infrastructures of the Internet have become highly publicized incidents and call for immediate solution. It is a complex and difficult problem characterized by an explicit attempt of the attackers to prevent access to resources by legitimate users for which they have authorization. Several schemes have been proposed on how to defend against these attacks, yet the problem still lacks a complete solution. The main purpose of this paper is therefore twofold. First is to present a comprehensive study of a wide range of DDoS attacks and defense methods proposed to combat them. This provides better understanding of the problem, current solution space, and future research scope to defend against DDoS attacks. Second is to propose an integrated solution for completely defending against flooding DDoS attacks at the Internet Service Provider (ISP) level.

An Efficient Gateway Discovery in Ad Hoc Networks for Internet Connectivity

Integration of MANET with the Internet is a challenging problem. It is important that dynamically deployed wireless ad hoc networks should also gain access to Internet multimedia contents through these fixed networks. When a mobile node in an Ad Hoc network wants to communicate with a node on the Internet, it has to find an efficient and reliable Internet gateway. For this purpose, the node either can send solicitation message or may depend on periodic gateway advertisement. Gateway discovery time has strong influence on packet delay and throughput. In most of the cases, a mobile node uses a number of physical hops to a gateway to communicate with a fixed host connected to an Internet. However, a minimum hop path may not always be efficient if some nodes along the path have longer queue of waiting packets. The focus of this paper is on devising an efficient proactive gateway discovery algorithm that takes into account the size of interface queue in addition to the traditional minimum hop metric to select an efficient gateway. In the MANET domain, AODV routing protocol has been used. This approach also allows an efficient handoff from one gateway to another gateway and still maintains a seamless connectivity to a fixed host. In this paper, impacts of this new metric on the gateway discovery performance are investigated. Simulation results indicate that our protocol outperforms other approaches.

Efficient Cooperative Caching in Ad Hoc Networks

Caching of frequently accessed data in multi-hop ad hoc environment is a potential technique that can improve the data access performance and availability. Cooperative caching, which allows the sharing and coordination of cached data among clients, can further explore the potential of the caching techniques. In this paper, we propose a novel scheme, called zone cooperative (ZC) for caching in mobile ad hoc networks. In ZC scheme, one-hop neighbors of a mobile client form a cooperative cache zone since the cost for communication with them is low both in terms of energy consumption and message exchange. As a part of cache management, cache admission control and VALUE based replacement policy are developed to improve the data accessibility and reduce the local cache miss ratio. An analytical study of ZC based on data popularity, node density and transmission range is also performed. Simulation experiments show that the ZC caching mechanism achieves significant improvements in cache hit ratio and average query latency in comparison with other caching strategies

A weighted cache replacement policy for location dependent data in mobile environments

Developing widely useful mobile computing applications presents difficult challenges. On one hand, mobile users demand intuitive user interfaces, fast response times, and deep relevant content. On the other hand, mobile devices have limited processing, storage, power, display, and communication resources. Caching frequently accessed data items on the mobile client is an effective technique to improve the system performance in mobile environment. Due to cache size limitation, the choice of cache replacement technique to find a suitable subset of items for eviction from cache becomes important. In this paper, we propose a new cache replacement policy for location dependent data in mobile environment. The proposed policy selects the predicted region based on clients movement and uses it to calculate the weighted data distance of an item. This makes the policy adaptive to clients movement pattern and provides importance to the regions around clients position. This is unlike earlier policies that consider the directional/non-directional data distance only. We call our policy the Weighted Predicted Region based Cache Replacement Policy (WPRRP). Simulation results show that the proposed policy significantly improves the system performance in comparison to previous schemes in terms of cache hit ratio.

A Routing Protocol for Delay-Sensitive Applications in Mobile Ad Hoc Networks

The Ad hoc On Demand Distance Vector (AODV) routing protocol is intended for use by mobile nodes in ad hoc networks. To provide quality of service, extensions can be added to the messages used during route discovery. These extensions specifythe service requirements which must be met by nodes rebroadcasting a route request (RREQ) or returning a route reply (RREP) for a destination. In order to provide quality delivery to delay sensitive applications such as voice and video, it is extremely important that mobile ad hoc networks provide quality of service (QoS) support in terms of bandwidth and delay. In spite of using IEEE 802.11 as medium access control (MAC), most of the ad hoc routing protocols do not consider contention time which occurs in the medium reservation. Large contention times can be more critical than hop counts in determining the end-to-end delay. Most existing routing protocols for mobile ad hoc networks are designed to search for the shortest path with minimum hop counts. However, the shortest routes do not always provide the best performance, especially when there are congested nodes along these routes. In this paper we propose an on demand delay based quality of service (QoS) routing protocol (AODV-D) to ensure that delay does not exceed a maximum value for mobile ad hoc networks. This protocol will take into consideration MAC layer channel contention information and the number of packets in the interface queue in addition to minimum hops.