Anand, Madhukar
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Publication An Analysis Framework for Network-Code Programs(2006-07-19) Anand, Madhukar; Fischmeister, Sebastian; Lee, InsupDistributed real-time systems require a predictable and verifiable mechanism to control the communication medium. Current real-time communication protocols are typically independent of the application and have intrinsic limitations that impede customizing or optimizing them for the application. Therefore, either the developer must adapt her application and work around these subtleties or she must limit the capabilities of the application being developed. Network Code, in contrast, is a more expressive and flexible model that specifies real-time communication schedules as programs. By providing a programmable media access layer on the basis of TDMA, Network Code permits creating application-specific protocols that suit the particular needs of the application. However, this gain in flexibility also incurrs additional costs such as increased communication and run-time overhead. Therefore, engineering an application with network code necessitates that these costs are analyzed, quantified, and weighted against the benefits. In this work, we propose a framework to analyze network code programs for commonly used metrics such as overhead, schedulability, and average waiting time. We introduce Timed Tree Communication Schedules, based on timed automata to model such programs and define metrics in the context of deterministic and probabilistic communication schedules. To demonstrate the utility of our framework, we study an inverted pendulum system and show that we can decrease the cumulative numeric error in the model’s implementation through analyzing and improving the schedule based on the presented metrics.Publication Sensor Network Security: More Interesting Than You Think(2006-07-31) Anand, Madhukar; Cronin, Eric; Sherr, Micah; Blaze, Matthew A; Ives, Zachary G; Lee, InsupWith the advent of low-power wireless sensor networks, a wealth of new applications at the interface of the real and digital worlds is emerging. A distributed computing platform that can measure properties of the real world, formulate intelligent inferences, and instrument responses, requires strong foundations in distributed computing, artificial intelligence, databases, control theory, and security. Before these intelligent systems can be deployed in critical infrastructures such as emergency rooms and powerplants, the security properties of sensors must be fully understood. Existing wisdom has been to apply the traditional security models and techniques to sensor networks. However, sensor networks are not traditional computing devices, and as a result, existing security models and methods are ill suited. In this position paper, we take the first steps towards producing a comprehensive security model that is tailored for sensor networks. Incorporating work from Internet security, ubiquitous computing, and distributed systems, we outline security properties that must be considered when designing a secure sensor network. We propose challenges for sensor networks – security obstacles that, when overcome, will move us closer to decreasing the divide between computers and the physical world.Publication Distributed-Code Generation from Hybrid Systems Models for Time-delayed Multirate Systems(2005-09-19) Anand, Madhukar; Fischmeister, Sebastian; Kim, Jesung; Lee, InsupHybrid systems are an appropriate formalism to model embedded systems as they capture the theme of continuous dynamics with discrete control. A simple extension, a network of communicating hybrid automata, allows for modeling distributed embedded systems. Although it is possible to generate code from such models, it is difficult to provide formal guarantees in the code with respect to the model. One of the reasons for this is that, the model is set in continuous time and concurrent execution with instantaneous communication, whereas the generated code is set in discrete time with delayed communication. This can introduce semantic differences between the model and the code such as missed transitions, faulty transitions, and altered continuous behavior. The goal of faithful code generation is to minimize these differences. In this paper, we propose a relaxed criteria of relative faithful implementation. Based on this criteria, we propose dynamically adjusting the guard at runtime using estimates of errors for preventing faulty transitions. We also identify a sufficient condition to ensure no missed transitions in the code.Publication A Dynamic Scheduling Approach to Designing Flexible Safety-Critical Systems(2007-10-01) Anand, Madhukar; Fischmeister, Sebastian; Almeida, Luis; Lee, InsupThe design of safety-critical systems has typically adopted static techniques to simplify error detection and fault tolerance. However, economic pressure to reduce costs is exposing the limitations of those techniques in terms of efficiency in the use of system resources. In some industrial domains, such as the automotive, this pressure is too high, and other approaches to safety must be found, e.g., capable of providing some kind of fault tolerance but with graceful degradation to lower costs, or also capable of adapting to instantaneous requirements to better use the computational/communication resources. This paper analyzes the development of systems that exhibit such level of flexibility, allowing the system configuration to evolve within a well-defined space. Two options are possible, one starting from the typical static approach but introducing choice points that are evaluated only at runtime, and another one starting from an open systems approach but delimiting the space of possible adaptations. The paper follows the latter and presents a specific contribution, namely, the concept of local utilization bound, which supports a fast and efficient schedulability analysis for on-line resource management that assures continued safe operation. Such local bound is derived off-line for the specific set of possible configurations, and can be significantly higher than any generic non-necessary utilization bound such as the well known Liu and Layland’s bound for Rate-Monotonic scheduling.Publication Security Protocols With Isotropic Channels(2006-01-01) Anand, Madhukar; Cronin, Eric; Sherr, Micah; Blaze, Matthew A; Kannan, SampathWe investigate the security properties of isotropic channels, broadcast media in which a receiver cannot reliably determine whether a message originated from any particular sender and a sender cannot reliably direct a message away from any particular receiver. We show that perfect isotropism implies perfect (information-theoretic) secrecy, and that asymptotically close to perfect secrecy can be achieved on any channel that provides some (bounded) uncertainty as to sender identity. We give isotropic security protocols under both passive and active adversary models, and discuss the practicality of realizing isotropic channels over various media.Publication Compositional Analysis Framework using EDP Resource Models(2007-12-03) Easwaran, Arvind; Anand, Madhukar; Lee, InsupCompositional schedulability analysis of hierarchical scheduling frameworks is a well studied problem, as it has wide-ranging applications in the embedded systems domain. Several techniques, such as periodic resource model based abstraction and composition, have been proposed for this problem. However these frameworks are sub-optimal because they incur bandwidth overhead. In this work, we introduce the Explicit Deadline Periodic (EDP) resource model, and present compositional analysis techniques under EDF and DM. We show that these techniques are bandwidth optimal, in that they do not incur any bandwidth overhead in abstraction or composition. Hence, this framework is more efficient when compared to existing approaches.Publication Quantifying Eavesdropping Vulnerability in Sensor Networks(2005-08-29) Anand, Madhukar; Ives, Zachary G; Lee, InsupWith respect to security, sensor networks have a number of considerations that separate them from traditional distributed systems. First, sensor devices are typically vulnerable to physical compromise. Second, they have significant power and processing constraints. Third, the most critical security issue is protecting the (statistically derived) aggregate output of the system, even if individual nodes may be compromised. We suggest that these considerations merit a rethinking of traditional security techniques: rather than depending on the resilience of cryptographic techniques, in this paper we develop new techniques to tolerate compromised nodes and to even mislead an adversary. We present our initial work on probabilistically quantifying the security of sensor network protocols, with respect to sensor data distributions and network topologies. Beginning with a taxonomy of attacks based on an adversary’s goals, we focus on how to evaluate the vulnerability of sensor network protocols to eavesdropping. Different topologies and aggregation functions provide different probabilistic guarantees about system security, and make different trade-offs in power and accuracy.Publication Generating Sound and Resource-Aware Code from Hybrid System Models(2006-03-15) Anand, Madhukar; Kim, Jesung; Fischmeister, Sebastian; Lee, InsupModern real-time embedded systems are complex, distributed, feature-rich applications. Model-based development of real-time embedded systems promises to simplify and accelerate the implementation process. Although there are appropriate models to design such systems and some tools that support automatic code generation from such models, several issues related to ensuring correctness of the implementation with respect to the model remain to be addressed. In this work, we investigate how we can derive sampling rates for distributed real-time systems generated from a hybrid systems model such that there are no switching discrepancies and the resources spent in achieving this are a minimum. Of particular interest are the resulting mode switching semantics and we propose an approach to handle faulty transitions and compute execution rates for minimizing missed transitions. As a guiding example for our approach, we describe a hybrid systems model for vehicle coordination in which one vehicle acts as a leader and a second follows the leader guaranteeing to maintain a safe distance between the two vehicles.Publication Robust Test Generation and Coverage for Hybrid Systems(2007-04-01) Julius, Agung; Fainekos, Georgios E; Anand, Madhukar; Lee, Insup; Pappas, GeorgeTesting is an important tool for validation of the system design and its implementation. Model-based test generation allows to systematically ascertain whether the system meets its design requirements, particularly the safety and correctness requirements of the system. In this paper, we develop a framework for generating tests from hybrid systems’ models. The core idea of the framework is to develop a notion of robust test, where one nominal test can be guaranteed to yield the same qualitative behavior with any other test that is close to it. Our approach offers three distinct advantages: 1) It allows for computing and formally quantifying the robustness of some properties; 2) it establishes a method to quantify the test coverage for every test case; and 3) the procedure is parallelizable and therefore, very scalable. We demonstrate our framework by generating tests for a navigation benchmark application.Publication Code Generation from Hybrid Systems Models for Distributed Embedded Systems(2005-05-18) Anand, Madhukar; Kim, Jesung; Lee, InsupCode generation from hybrid system models is a promising approach to producing reliable embedded systems. This approach presents new challenges as the precise semantics of the model are hard to capture in the code. A framework for generating code was introduced for single threaded/processor environments. Here, we extend it by considering code generation for distributed environments. We also define criteria for faithful implementation of the model. To this end, we define faulty and missed transitions. For preventing faulty transitions, we build on the idea of instrumentation we have developed for sound simulation of hybrid systems. Finally, we present sufficient conditions to avoid missed transitions and provide examples.