INESC-ID

About: INESC-ID is a nonprofit organization based out in Lisbon, Portugal. It is known for research contribution in the topics: Field-programmable gate array & Control theory. The organization has 932 authors who have published 2618 publications receiving 37658 citations.

Towards distributed software transactional memory systems

Abstract: The recent architectural trend that has lead to the widespread adoption of multi-core CPUs has fostered a remarkable research interest in Software Transactional Memory (STM). As STMs are starting to face the high availability and scalability requirements of real-world production environments, it is natural to foresee the need for replication solutions specifically tailored for STMs. Since databases and STMs share the same key abstraction of atomic transaction, one could wonder whether the mechanisms originally designed for database replication could be successfully and seamlessly exploited also to support replication of STM systems.This paper seeks an answer to this question, highlighting some critical performance issues related to the application of state of the art database replication techniques in the context of STM systems, and presenting some of our recent research directions aimed at designing and implementing high performance replication strategies able to meet the unique requirements of STMs.

Improving the functionality of syn cookies

Abstract: Current Linux kernels include a facility called TCP SYN cookies, conceived to face SYN flooding attacks. However, the current implementation of SYN cookies does not support the negotiation of TCP options, although some of them are relevant for throughput performance, such as large windows or selective acknowledgment. In this paper we present an improvement of the SYN cookie protocol, using all the current mechanisms for generating and validating cookies while allowing connections negotiated with SYN cookies to set up and use any TCP options. The key idea is to exploit a kind of TCP connection called “simultaneous connection initiation” in order to lead client hosts to send together TCP options and SYN cookies to a server being attacked.

Mid-air interactions above stereoscopic interactive tables

Abstract: Stereoscopic tabletops offer unique visualization capabilities, enabling users to perceive virtual objects as if they were lying above the surface. While allowing virtual objects to coexist with user actions in the physical world, interaction with these virtual objects above the surface presents interesting challenges. In this paper, we aim to understand which approaches to 3D virtual object manipulations are suited to this scenario. To this end, we implemented five different techniques based on the literature. Four are mid-air techniques, while the remainder relies on multi-touch gestures, which act as a baseline. Our setup combines affordable non-intrusive tracking technologies with a multi-touch stereo tabletop, providing head and hands tracking, to improve both depth perception and seamless interactions above the table. We conducted a user evaluation to find out which technique appealed most to participants. Results suggest that mid-air interactions, combining direct manipulation with six degrees of freedom for the dominant hand, are both more satisfying and efficient than the alternatives tested.

On Computing Backbones of Propositional Theories

Abstract: Backbones of propositional theories are literals that are true in every model. Backbones have been used for characterizing the hardness of decision and optimization problems. Moreover, backbones find other applications. For example, backbones are often identified during product configuration. Backbones can also improve the efficiency of solving computational problems related with propositional theories. These include model enumeration, minimal model computation and prime implicant computation. This paper investigates algorithms for computing backbones of propositional theories, emphasizing the integration of these algorithms with modern SAT solvers. Experimental results, obtained on representative problem instances, indicate that the proposed algorithms are effective in practice and can be used for computing the backbones of large propositional theories. In addition, the experimental results indicate that propositional theories can have large backbones, often representing a significant percentage of the total number of variables.