In this article, we propose the transaction scheduling for web service database transactions. Our solution ensures consistency while preserving efficiency. We propose a prediction-based metric that promotes transactions with reliable reputations based on the transactions performance metrics. Performance metrics are based on the transactions likelihood to commit and their execution time. We propose a customized lock management solution to guarantee execution consistency in concurrent web service environments. We formally prove that our solution guarantees consistent execution history of concurrent web transactions and increases concurrency and performance over traditional locking methods. We developed a simulation using a multi-threaded approach. We generated sample workloads of simulated concurrent transactions over seven tests. Our results show that the solution works comparatively with traditional locking and no-locking solutions with the added benefit of ensured consistency in some cases and deadlock avoidance in others.

Collaborative and competitive applications require that participants receive messages almost simultaneously and before a specified time. These requirements have been addressed by the delay variation-bounded multicasting tree (DVBMT) problem. In this paper, we propose the interval multicast subgraph (IMS) problem to address these requirements. IMS addresses these constraints with an interval of acceptable delay values for paths as user input from a source to a destination, eliminating the need to optimize delays for a variation value. By solving IMS rather than DVBMT and other variants of DVBMT, we are able to find solutions for larger graphs more efficiently. Our proposed interval multicast algorithm (IMA) accounts for an interval of acceptable delay as user input and guarantees the weight of each path from the source to a distinct destination is within the given interval if that path exists. We provide proofs of correctness and complexity of IMA, as well as simulation experiments, to illustrate the effects of various parameters on our algorithm. Simulations show that IMS is significantly less costly than finding the minimum variation for the average and best case. By remodeling the DVBMT problem to IMS, we have created a new problem that addresses the quality of service requirements of multicasting and is able to be solved efficiently for the average case for relatively large graphs.

Intrusion Detection in a network is defined as identifying activities which violate security policies. Traditional Intrusion Detection Systems (IDSs) are centralized in nature where a central node collects data from every node and detects whether any abnormal activity is taking place in the network. In our research we propose to use intelligent mobile agents to detect intrusions in a network. An agent is a piece of program which will execute specified operations on a node in a network. The agents act as guards which essentially roam the network periodically to check whether any node in the network is under attack. When an agent visits a node, it scans the log file to identify any abnormal activity taking place in that node. In our previous research we proposed algorithms for finding initial locations and roaming pattern of agents. In this research, we have built the prototype of an agent and deployed it in a virtual network to test its performance by simulating intrusions. We have also tested the performance of the prototype by deploying the agents on PlanetLab which is a testbed in the Internet connecting more than 1300 machines all over the world. From our experiments we have observed that the performance of the agent based intrusion detection system depends on the size and topology of the network.

In certain types of Internet applications, multicasting with Quality of Service (QoS) optimizations are required on both the end-to-end delay from the source to the destinations, as well as the difference in the end-to-end delay between the destinations. Examples of these applications include video-conferencing, online games, and distributed database replication. These applications require that the messages should reach all the destinations within a specified period of time and all the destinations should receive the message from the source almost at the same time. The solutions to the Delay and Delay Variation Bounded Multicast Network (DVBMN) problem involve generating a network which spans the source and the group of destinations such that the end-to-end delay from source to each destination is within a bound and the delay variation among all the destinations is minimum. The Chains heuristic proposed in the literature provides such a multicast network which achieves the tightest delay variation with minimum execution time. To test the performance of multicasting using the multicast network generated by Chains heuristic on the Internet, we have implemented a prototype of a multicast network using Chains and experimented multicasting with the prototype on PlanetLab. PlanetLab is an overlay testbed which connects more than 1000 nodes all over the world. We have analyzed the performance of multicasting using the prototype on PlanetLab. Results show that the measured value of maximum delay variation from the prototype approximately matches with the value calculated by Chains for a small number of destination nodes. However, as the number of destination nodes increases, the measured value of maximum delay variation from the prototype quickly increases.

Virtual world and other collaborative applications are increasingly becoming popular among Internet users. In such applications, users interact with each other through digital entities or avatars. In order to preserve the user experience, it is important that certain Quality of Service (QoS) requirements (e.g., delay and bandwidth) are satisfied by the interactions. These QoS requirements are usually defined by the application designer. When applications with such QoS requirements are being deployed on a network of servers, an appropriate set of servers capable of satisfying the QoS constraints of the interactions must be identified. This identification process is nothing, but the subgraph homeomorphism problem. In this paper, we present polynomial-time solutions for a special case of this problem viz. subtree homeomorphism problem, wherein the guest and the host graphs are both trees. We also discuss generalizations of the subtree homeomorphism problem and present polynomial-time solutions.

Distributed Virtual Environments (DVE) have become increasingly popular over the last few years. Examples of DVEs are Massively Multiplayer Online Games (MMOGs), distributed interactive simulations, and shared virtual worlds. The service providers of DVEs need to ensure that certain Quality of Servi

Collaborative multimedia applications (CMAs) on overlay networks are gaining popularity among users who are geographically dispersed. Examples of these kinds of applications include networked games and collaborative design and simulation. An important challenge in realizing CMAs is obtaining floor control, a problem in which the end-users compete among themselves to gain exclusive access to a shared resource. In this paper, we present deterministic and randomized distributed mechanisms for solving the floor control problem. In particular, we adapt the well-known MAC protocols viz. distributed queue dual bus (DQDB), ALOHA, and carrier sense multiple access (CSMA) as solutions for the floor control problem. Central to our adaptation is an algorithmic methodology that efficiently virtualizes the underlying network connecting the CMA participants so as to enhance the proposed solutions' performance. We present analytical and experimental studies on the performance of the proposed floor control protocols that bring out their essential characteristics.

Computer supported collaborative applications on overlay networks are gaining popularity among users who are geographically dispersed. Examples of these kinds of applications include video-conferencing, distributed database replication, and online games. This type of application requires a multicasting subnetwork, using which messages should arrive at the destinations within a specified delay bound. These applications also require that destinations receive the message from the source at approximately the same time. The problem of finding a multicasting subnetwork with delay and delay-variation bound has been proved to be an NP complete problem in the literature and heuristics have been proposed for this problem. In this paper, we provide an efficient heuristic to obtain a multicast subnetwork on an overlay network, given a source and a set of destinations that is within a specified maximum delay and a specified maximum variation in the delays from a source to the destinations. The time-complexity of our algorithm is O(|E|+nk log(|E|/n)+m2k), where n and |E| are the number of nodes and edges in the network, respectively, k is the number of shortest paths determined, and m is the number of destinations. We have shown that our algorithm is significantly better in terms of time-complexity than existing algorithms for the same problem. Our extensive empirical studies indicate that our heuristic uses significantly less runtime in comparison with the best-known heuristics while achieving the tightest delay variation for a given end-to-end delay bound

Computer supported collaborative applications on overlay networks are gaining popularity among users who are geographically dispersed. Examples of these kinds of applications include video-conferencing, collaborative design and simulation, distance learning, and online games. One of the important issues in collaborative applications is floor control wherein the end-users coordinate among themselves to gain exclusive access to the communication channel. An end-user who wins the floor, sends message to all other participating end-users. In this paper, to solve the floor control problem we present an implementation and evaluation of ALOHA and distributed queue dual bus (DQDB) distributed MAC (medium access control) protocols on overlay networks. As an initial step in the implementation of these MAC protocols, we propose an algorithm to construct an efficient communication channel among the Network Service Nodes (NSNs) in the overlay network. We also show that our implementation scheme (first one among decentralized floor control protocols) preserves the causal ordering of messages. We compare the efficiencies of the proposed implementation of floor control protocols using an analytical model that is verified using extensive simulation experiments.