Real-time image transmission is crucial to an emerging class of distributed embedded systems operating in open network environments. Examples include avionics mission re-planning over Link-16, security systems based on wireless camera networks, and online collaboration using camera phones. Meeting image transmission deadlines is a key challenge in such systems due to unpredictable network conditions. In this paper, we present CAMRIT, a Control-based Adaptive Middleware framework for Real-time Image Transmission in distributed real-time embedded systems. CAMRIT features a distributed feedback control loop that meets image transmission deadlines by dynamically adjusting the quality of image tiles. We derive an analytic model that captures the dynamics of a distributed middleware architecture. A control theoretic methodology is applied to systematically design a control algorithm with analytic assurance of system stability and performance, despite uncertainties in network bandwidth. Experimental results demonstrate that CAMRIT can provide robust real-time guarantees for a representative application scenario.

Distributed real-time and embedded (DRE) systems have stringent constraints on timeliness and other properties whose assurance is crucial to correct system behavior. Formal tools and techniques play a key role in verifying and validating system properties. However, many DRE systems are built using middleware frameworks that have grown increasingly complex to address the diverse requirements of a wide range of applications. How to apply formal tools and techniques effectively to these systems, given the range of middleware configuration options available, is therefore an important research problem.This paper makes three contributions to research on formal verification and validation of middleware-based DRE systems. First, it presents a reusable library of formal models we have developed to capture essential timing and concurrency semantics of foundational middleware building blocks provided by the ACE framework. Second, it describes domain-specific techniques to reduce the cost of checking those models while ensuring they remain valid with respect to the semantics of the middleware itself. Third, it presents a verification and validation case study involving a gateway service, using our models.

Thread allocation is an important problem in distributed real-time and embedded (DRE) systems. A thread allocation policy that is too liberal may cause deadlock, while a policy that is too conservative limits potential parallelism, thus wasting resources. However, achieving (globally) optimal thread utilization, while avoiding deadlock, has been proven impractical in distributed systems: it requires too much communication between components. In previous work we showed that efficient local thread allocation protocols are possible if the protocols are parameterized by global static data, in particular by an annotation of the global call graph of all tasks to be performed by the system. We proved that absence of cyclic dependencies in this annotation guarantees absence of deadlock. In this paper we present an algorithm to compute optimal annotations, that is annotations that maximize parallelism while satisfying the condition of acyclicity. Moreover, we show that the condition of acyclicity is in fact tight and exhibits a rather surprising anomaly: if a cyclic dependency is present in the annotation of the call graph and a certain minimum number of threads is provided, deadlock is reachable. Thus, in the presence of cyclic dependencies, increasing the number of threads may introduce the possibility of deadlock in an originally deadlock free system.

This paper describes a scheduling abstraction, called group scheduling, that emphasizes fine grain configurability of system scheduling semantics. The group scheduling approach described and evaluated in this paper provides an extremely flexible framework within which a wide range of scheduling semantics can be expressed, including familiar priority and deadline based algorithms. The paper describes both OS and middleware based implementations of the framework, and shows through evaluation that they can produce the same behavior for a nontrivial set of application computations. We also show that the framework can support application-specific scheduling constraints such as progress, to improve performance of applications whose scheduling semantics do not match those of traditional scheduling algorithms.

Summary form only given. Previous system scheduling approaches have focused primarily on system-level abstractions for scheduling decision functions and the mechanisms used to implement them. We introduce a new abstraction called group scheduling that focuses primarily on the progress of application-level computations and on organizing system-level scheduling abstractions to ensure that progress. We make three contributions to system scheduling research. First, it defines a model for group scheduling that augments and complements hierarchical scheduling models. Second, it describes how a computation's progress semantics can be mapped to scheduling mechanisms at the operating system and middleware levels. Third, it presents preliminary empirical studies of the performance of group scheduling in a realistic system environment.

General purpose middleware has been shown to be effective off-the-shelf, in meeting diverse functional requirements for a wide range of distributed systems. However, middleware customization is necessary for many networked embedded systems because of the resource constraints in the networked nodes. We demonstrate that reduced middleware footprint can be achieved while maintaining real-time properties of applications running on such systems. We also give evidence that empirical measurement using a representative application is crucial to guide (1) selection of feature subsets from general purpose middleware and (2) trade-offs among different dimensions of design metrics including real-time, footprint, and portability.

Real-time image transmission is crucial to an emerging class of distributed embedded systems operating in open network environments. Examples include avionics mission re-planning over Link-16, security systems based on wireless camera networks, and online collaboration using camera phones. Meeting image transmission deadlines is a key challenge in such systems due to unpredictable network conditions. In this paper, we present CAMRIT, a control-based adaptive middleware framework for real-time image transmission in distributed real-time embedded systems. CAMRIT features a distributed feedback control loop that meets image transmission deadlines by dynamically adjusting the quality of image tiles. We derive an analytic model that captures the dynamics of a distributed middleware architecture. A control theoretic methodology is applied to systematically design a control algorithm with analytic assurance of system stability and performance, despite uncertainties in network bandwidth. Experimental results demonstrate that CAMRIT can provide robust real-time guarantees for a representative application scenario.

QoS-enabled component middleware solutions can help reduce the programming complexity of configuring real-time aspects, such as priorities and rates of invocation. However, few empirical studies have been conducted to guide distributed real-time and embedded (DRE) system developers in choosing among alternative configuration mechanisms and performance optimization techniques in practice. This paper makes three contributions to research on QoS-enabled component middleware for DRE systems in the context of the component-integrated ACE ORB (CIAO). First, it describes the design of CIAO's static component configuration mechanisms, which enhance configurability by avoiding features that are not supported by key real-time platforms, while reducing run-time overhead and footprint. Second, it compares the performance of dynamic and static configuration mechanisms in CIAO to help guide the selection of suitable configuration mechanisms based on specific requirements of each DRE system. Third, it presents an empirical comparison of CIAO's static configuration mechanisms to the static configuration mechanisms in Boeing's PRISM avionics component middleware solution.