Leaky prediction layered video coding (LPLC) partially includes the enhancement layer in the motion compensated prediction loop, by using a leaky factor between 0 and 1, to balance the coding efficiency and error resilience performance. In this paper, rate distortion functions are derived for LPLC from rate distortion theory. Closed form expressions are obtained for two scenarios of LPLC, one where the enhancement layer stays intact and the other where the enhancement layer suffers from data rate truncation. The rate distortion performance of LPLC is then evaluated with respect to different choices of the leaky factor, demonstrating that the theoretical analysis well conforms with the operational results.

The block DCT (BDCT) is by far one of the most popular transforms used in image and video coding. However, it introduces a noticeable blocking artifact at low data rates. A great deal of work has been done to remove the artifact with information extracted from the spatial and frequency domains. In this paper we address the video sequence restoration problem as a 3D Huber-Markov random field model and derive the temporal extension to traditional maximum a posteriori (MAP)-based methods. Two schemes, we call temporal MAP (TMAP) and motion compensated TMAP (MC-TMAP) respectively, are presented. We test our methods on MPEG-2 compressed sequences and evaluate their performances with traditional MAP restoration. Experimental results confirm that our schemes can significantly improve the visual quality of the reconstructed sequences.

We investigate the performance issues of destination-sequenced distance vector (DSDV) and ad-hoc on-demand distance vector (AODV) routing protocols for mobile ad hoc networks. Four performance metrics are measured by varying the maximum speed of mobile hosts, the number of connections, and the network size. The correlation between network topology change and mobility is investigated by using linear regression analysis. The simulation results indicate that AODV outperforms DSDV in less stressful situations, while DSDV is more scalable with respect to the network size. It is observed that network congestion is the dominant reason for packet drop for both protocols. We propose a new routing protocol, congestion-aware distance vector (CADV), to address the congestion issues. CADV outperforms AODV in delivery ratio by about 5%, while introduces less protocol load. The result demonstrates that integrating congestion avoidance mechanisms with proactive routing protocols is a promising way to improve performance.

Action frauds constitute largest part of all Internet frauds. Cheating is a kind of fraud that does not have direct evidences of its occurrence. We conduct theoretical studies as well as simulation experiments to find out the effect of cheating in three important types of auctions: English auction, first-price sealed-bid, and second-price sealed-bid auction. Our cheating environment consists of shill bidding, bid shading and false bidding in English, first-price and second-price auction, respectively. In the experiments ordinary bidders, bidders with the equilibrium bidding strategy, and cheaters compete with each other. Both theoretical and experimental results confirm that the equilibrium bidding strategies indeed increases the bidders’ expected utility. Therefore, it can be concluded that adoption of rational bidding strategies can combat cheating. It is found that most of the auction sites intuitively prefer English auction to other auction mechanisms. There is not much theoretical or experimental evidence to support such an intuition. We use honest bidder’s expected gain and honest seller’s revenue loss as a basis to compare these three important auctions types. The analysis of the results reveals English auction to be the most preferred mechanism from both honest buyer’s and honest seller’s point of view. This result can be used as an experimental evidence to explain the popularity of English auction over the Internet.

Most of the proposed security protocols for wireless sensor networks (WSN) are designed to provide the uniform level of security across the network. There are various multi-sensing applications like sensors monitoring airport runway control system which may also be used to monitor environmental conditions such as wind speed and direction. When these nodes communicate, they may require different levels of security. For example, in case of a highjack event, the secure communication among nodes in a target region in the airport runway control system should be provided as they exchange highly critical data. In this paper, we propose a scheme called role-based access in sensor networks (RBASH) which provides role-based multilevel security in sensor networks. Each group is organized in such a way that they can have different roles based on the context and thus, can provide or have different levels of accesses. RBASH provides the desired security level based on the application need. The multilevel security is based on assigned keys to different nodes at different levels. To achieve this goal, we organize the network using Hasse diagram then compute the key for each individual node and extend it further to construct the key for a group. Based on experimental observations, we conclude that RBASH is energy and communication efficient in providing security compared to some other protocols which provides uniform security for all the nodes.

Trust - “reliance on the integrity, ability, or character of a person or thing” - is pervasive in social systems. We constantly apply it in interactions between people, organizations, animals, and even artifacts. We use it instinctively and implicitly in closed and static systems, or consciously and explicitly in open or dynamic systems. An epitome for the former case is a small village, where everybody knows everybody, and the villagers instinctively use their knowledge or stereotypes to trust or distrust their neighbors. A big city exemplifies the latter case, where people use explicit rules of behavior in diverse trust relationships. We already use trust in computing systems extensively, although usually subconsciously. The challenge for exploiting trust in computing lies in extending the use of trust-based solutions, first to artificial entities such as software agents or subsystems, then to human users’ subconscious choices.

Digital libraries involve various types of data like text, audio, images and video. The data objects are typically very large and of the order of hundreds and thousands of kilobytes. In a digital library, these data objects are distributed in a wide area network. Retrieving large data objects in a wide area network has a high response time. We have conducted experiments to measure the communication overhead in the response time. We have studied the correlation between communication and size of data, between communication and type of data and the communication delay to various sites in a local and wide area network. We present different strategies for reducing delay while communicating multimedia data. Images are amenable to losing data without losing semantics of the image. Lossy compression techniques reduce the quality of the image and reduce the size leading to a lower communication delay. We compared the communication delay between compressed and uncompressed images and study the overhead due to compression and decompression. We present issues in providing digital library service to mobile users and discuss a question: What if communication were free? Finally, we present a framework for efficient communication of digital library data.

Multiversions of data are used in database systems to increase concurrency and to provide efficient recovery. Data versions improve the concurrency by allowing the concurrent execution of “non-conflicting” read-write lock requests on different versions of data in an arbitrary fashion. A transaction that accesses a data item version, which later diagnosed to lead to an incorrect execution, is aborted. This act is reminiscent of the validation phase in the optimistic concurrency control schemes. Various performance studies suggest that these schemes perform poorly in high data contention environments where the excessive transaction aborts result due to the failed validation. We propose an adaptable constrained two-version two-phase locking (C2V2PL) scheme in which these “non-conflicting” requests are allowed only in a constrained manner. C2V2PL scheme assumes that a lock request failing to satisfy the specific constraints will lead to an incorrect execution and hence, must be either rejected or blocked. This eliminates the need for a separate validation phase. When the contention for data among the concurrent transactions is high, the C2V2PL scheduler in aggressive state rejects such lock requests. The deadlock free nature of C2V2PL scheduler adapts to the low data contention environments by accepting the lock request that have failed the specific constraints but contrary to the assumption, will not lead to an incorrect execution. Thus, C2V2PL scheme improves the potential concurrency due to reduced transaction aborts in this conservative state. We have compared performance of our scheme with other lock-based concurrency control schemes such as two phase locking, Wait-depth locking and Optimistic locking schemes. Our results show increase in throughput and reduced transaction-abort-ratio in case of C2V2PL scheme.

Ideas that are used in the design, development, and performance of concurrency control mechanisms have been summarized. The locking, time-stamp, optimistic-based mechanisms are included. The ideas of validation in the optimistic approach are presented in some detail. The degree of concurrency and classes of serializability for various algorithms have been presented. Questions that relate arrival rate of transactions with degree of concurrency and performance have been briefly presented. Finally, several useful ideas for increasing concurrency have been summarized. They include flexible transactions, adaptability, prewrites, multidimensional time stamps, and relaxation of two-phase locking

We discuss various secured Web access schemes using dynamic and static approaches. In a static approach the access environment, that is, the set of authorized users, the mode of access, their access rights, etc., are predefined. This approach is suitable only for a static set up where the user requirements do not change frequently. In the dynamic approach, on the other hand, the authorized user set is defined when Web pages access requests appear. An interested user to the Web is authenticated by necessary information provided by the user. Once the information is verified, the user is either given conditional access, timed access, or full access only to the information relevant to the user

In this paper, we present a version of the linear hash structure algorithm to increase concurrency using multi-level transaction model. We exploit the semantics of the linear hash operations at each level of transaction nesting to allow more concurrency. We implement each linear hash operation by a sequence of operations at lower level of abstraction. Each linear hash operation at leaf-level is a combination of search and read/write operations. We consider locks at both vertex (page) and key level (tuple) to further increase concurrency. As undo-based recovery is not possible with multi-level transactions, we use compensation-based undo to achieve atomicity. We have implemented our model using object-oriented technology and multithreading paradigm. In our implementation, linear hash operations such as find, insert, delete, split, and merge are implemented as methods and correspond to multi-level transactions.

The Indiana Center for Database Systems (ICDS) at Purdue University has embarked in an ambitious endeavor to become a premiere world-class database research center. This goal is substantiated by the diversity of its research topics, the large and diverse funding base, and the steady publication trend in top conferences and journals. ICDS was founded with an initial grant from the State of Indiana Corporation of Science and Technology in 1990. Since then it has grown to now have 9 faculty members and about 30 total researchers. This report describes the major research projects underway at ICDS as well as efforts to move research toward practice.

Data mining technology has given us new capabilities to identify correlations in large data sets. This introduces risks when the data is to be made public, but the correlations are private. We introduce a method for selectively removing individual values from a database to prevent the discovery of a set of rules, while preserving the data for other applications. The efficacy and complexity of this method are discussed. We also present an experiment showing an example of this methodology.

Secure Multi-Party Computation enables parties with private data to collaboratively compute a global function of their private data, without revealing that data. The increase in sensitive data on networked computers, along with improved ability to integrate and utilize that data, make the time ripe for practical secure multi-party computation. This paper surveys approaches to secure multi-party computation, and gives a method whereby an efficient protocol for two parties using an untrusted third party can be used to construct an efficient peer-to-peer secure multi-party protocol.