Large-scale wireless sensor networks represent a new generation of real-time embedded systems with significantly different communication constraints from traditional networked systems. This paper presents RAP, a new real-time communication architecture for large-scale sensor networks. RAP provides convenient, high-level query and event services for distributed micro -sensing applications. Novel location-addressed communication models are supported by a scalable and light-weight network stack. We present and evaluate a new packet scheduling policy called velocity monotonic scheduling that inherently accounts for both time and distance constraints. We show that this policy is particularly suitable for communication scheduling in sensor networks in which a large number of wireless devices are seamlessly integrated into a physical space to perform real-time monitoring and control. Detailed simulations of representative sensor network environments demonstrate that RAP significantly reduces the end-to-end deadline miss ratio in the sensor network.

In this paper, we propose and analyze a methodology for providing absolute differentiated services for real-time applications in networks that use static-priority schedulers. We extend previous work on worst-case delay analysis and develop a method that can be used to derive delay bounds without specific information on flow population. With this new method, we are able to successfully employ a utilization-based admission control approach for flow admission. This approach does not require explicit delay computation at admission time and hence is scalable to large systems. We assume the underlying network to use static-priority schedulers. We design and analyze several priority assignment algorithms, and investigate their ability to achieve higher utilization bounds. Traditionally, schedulers in differentiated services networks assign priorities on a classby -class basis, with the same priority for each class on each router. In this paper, we show that relaxing this requirement, that is, allowing different routers to assign different priorities to classes, achieves significantly higher utilization bounds.

In this paper we present the design, implementation and evaluation of a simple, practical and cost effective localization solution, called Walking GPS, that can be used in real, manual deployments of WSN. We evaluate our localization solution exclusively in real deployments of MICA2 and XSM motes. Our experiments show that 100 % of the deployed motes localize (i.e,. have a location position) and that the average localization errors are within 1 to 2 meters, due mainly to the limitations of the existing commercial GPS devices. 1.

In this paper, we present a methodology to apply utilization-based admission control

In this paper, we propose an approach to flow-unaware admission control, which is combination with an aggregate packet forwarding scheme, improves scalability of networks while guaranteeing end-to-end deadlines for realtime applications. We achieve this by using an off-line delay computation and verification step, which allows to reduce the overhead at admission control while keeping admission probability and resources utilization high. Our evaluation data show our system’s admission probabilities are very close to those of significantly more expensive flow-aware approaches. At the same time, admission control overhead during flow establishment is very low. Our results therefore support the claim from the DS architecture literature that scalability can be achieved through flow aggregation without sacrificing resource utilization and with significant reduction in run time overhead. 1.

We propose a network-based endpoint admission control system for scalable QoS guaranteed real-time communication services. This system is based on a sink tree-based resource management strategy, and is particularly well suited for differentiated-services based architectures. By performing the admission decision at the endpoints, the flow setup latency and the signaling overhead are kept to a minimum. In addition, the proposed system integrates routing and resource reservation along the routes, and therefore displays higher admission probability and better link resource utilization. This approach achieves low overall admission control overhead because much of the delay computation is done during system configuration, and so resources can effectively be preallocated before run time. We investigate a number of resource sharing approaches that allow resources to be efficiently re-allocated at run time with minimized additional overhead. We provide simulation experiments that illustrate the benefits of using sink tree-based resource management for resource pre-allocation and for routing, both with and without resource sharing.

This paper presents a new schedulability analysis methodology for distributed hard real-time systems with bursty job arrivals. The schedulability is analyzed by comparing worst-case response times of jobs with their timing constraints. We compute response times with a new method, which uses the amount of received service time to determine the response time of instances of a job. We illustrate how this method can be applied to exactly determine worstcase response times for processors with preemptive staticpriority schedulers, and how it gives a good approximation on the response times for processors with non-preemptive static-priority scheduling or first-come-first-served scheduling. Our schedulability analysis method is the first to support systems with arbitrary job arrival patterns. Nevertheless, it performs better than other known approaches used for systems with periodic job arrivals. 1. Introduction In a distributed real-time system, jobs have stringent timing constraints and of...

While the quality of service (QoS) profiles for a number of general packet radio service (GPRS) classes has been specified [1] by ETSI, how QoS management is provided by means of traffic scheduling, traffic shaping, and connection admission control, in a GPRS network is an implementation issue that is attracting significant current research interest. This paper presents an evaluation of several traffic scheduling methods, including of FIFO, Static Priority Scheduling (SPS) and Earliest Deadline First (EDF) by simulations, with the objective of meeting the delay profiles defined for a number of GPRS classes. Traffic sources representative of GPRS applications, including email, fleet management and world wide web applications are employed. We focus on the forward link which represents the bottleneck of a typical GPRS data connection. Results show that EDF is able to meet the delay requirements at a much higher channel utilization compared to the other alternatives. I.

Distributed mission critical systems require support for ultra-secure communication, in which intrusions must be detected and suppressed in real time, possibly before the affected messages reach the receiver. When the distributed application has real-time requirements, the effects of intrusion are particularly severe. In addition to covered channels and potentially tampered data at the receiver, such systems may experience violations of timing requirements and timing instabilities in components not directly related to the intrusion. Systems with real-time requirements have admission and access control mechanisms in place to ensure that timing requirements can be met during normal operation. Such admission control mechanisms require load profiles of traffic (for example in form of leaky bucket descriptors) so that resources can be appropriately allocated to meet application requirements during system operation. In this paper, we report on our project aiming at real-time detection of int...

: For admitting a hard real-time connection to an ATM network, it is required that the end-to-end delays of cells belonging to the connection meet their deadlines without violating the guarantees already provided to the currently active connections. There are two kinds of methods to analyze the endto -end delay in an ATM network. A decomposed method analyzes the worst case delay for each switch and then computes the total delay as the sum of the delays at individual switches. On the other hand, an integrated method analyzes all the switches involved in an integrated manner and derives the total delay directly. In this paper, we present an efficient and effective integrated method to compute the end-to-end delay. We evaluate the network performance under different system parameters and we compare the performance of the proposed method with the conventional decomposed and other integrated methods [1], [3], [5-9]. Index Terms: Real-Time Communication, ATM Networks, Endto -End Delay Analy...