Hung-Ying Tyan

J-Sim: a simulation and emulation environment for wireless sensor networks

Wireless sensor networks have gained considerable attention in the past few years. They have found application domains in battlefield communication, homeland security, pollution sensing, and traffic monitoring. As such, there has been an increasing need to define and develop simulation frameworks for carrying out high-fidelity WSN simulation. In this article we present a modeling, simulation, and emulation framework for WSNs in J-Sim - an open source, component-based compositional network simulation environment developed entirely in Java. This framework is built on the autonomous component architecture and extensible internetworking framework of J-Sim, and provides an object-oriented definition of target, sensor, and sink nodes, sensor and wireless communication channels, and physical media such as seismic channels, mobility models, and power models (both energy-producing and energy-consuming components). Application-specific models can be defined by subclassing classes in the simulation framework and customizing their behaviors. We also include in J-Sim a set of classes and mechanisms to realize network emulation. We demonstrate the use of the proposed WSN simulation framework by implementing several well-known localization, geographic routing, and directed diffusion protocols, and perform performance comparisons (in terms of the execution time incurred and memory used) in simulating WSN scenarios in J-Sim and ns-2. The simulation study indicates the WSN framework in J-Sim is much more scalable than ns-2 (especially in memory usage). We also demonstrate the use of the WSN framework in carrying out real-life full-fledged Future Combat System (FCS) simulation and emulation

J-Sim: A Simulation Environment for Wireless Sensor Networks

Wireless sensor networks (WSNs) have gained considerable attention in the past few years. As such, there has been an increasing need for defining and developing simulation frameworks for carrying out high-fidelity WSN simulation. In this paper, the authors presented a modeling and simulation framework for WSNs in J-Sim - an open-source, component-based compositional network simulation environment that is developed entirely in Java. This framework is built upon the autonomous component architecture (ACA) and the extensible internetworking framework (INET) of J-Sim, and provides an object-oriented definition of (i) target, sensor and sink nodes, (ii) sensor and wireless communication channels, and (iii) physical media such as seismic channels, mobility model and power model (both energy-producing and energy-consuming components). Application-specific models can be defined by sub-classing classes in the simulation framework and customizing their behaviors. The use of the proposed WSN simulation framework was demonstrated by implementing several well-known localization, geographic routing, and directed diffusion protocols. In addition, performance comparisons were performed (in terms of execution time incurred, and the memory used) in simulating several typical WSN scenarios in J-Sim and ns-2. The simulation study indicates that the proposed WSN simulation framework in J-Sim is much more scalable than ns-2 (especially in memory usage).

A better polynomial-time schedulability test for real-time fixed-priority scheduling algorithms

The problem of scheduling real-time periodic task has been studied extensively since its first introduction by C.L. Liu and J.W. Layland in their classic paper (1973). Due to several merits of the fixed-priority scheduling scheme, a lot of research work has focused on the analysis of fixed-priority scheduling algorithms. For the case that the deadlines of the executions of all the tasks coincide with the ends of their corresponding periods. Liu and Layland derived a worst-case utilization bound for a task set to be schedulable by the rate-monotonic (RM) algorithm. A. Burchard et al. (1995) presented another schedulability condition for RM, which has a higher utilization bound under a certain task condition. Although their closed-form utilization bounds provide a convenient way for testing the schedulability of a task set under the RM algorithm, the schedulability test using their bounds is too pessimistic since a lot of task sets with total utilizations larger than their bounds (and less than or equal to 1) are still schedulable by RM. In this paper, we propose a polynomial-time schedulability test and prove that it is better than Liu and Laylands and Burchards utilization bounds in the sense that as long as the total utilization of a task set is less than or equal to their bounds, our schedulability test will always answer positively for the schedulability of the task set under RM and even if a feasible task set has a total utilization larger than their bounds, our schedulability test will still answer positively with a high probability. We also show how to generalize our polynomial-time schedulability test to handle general task sets scheduled by arbitrary fixed-priority scheduling algorithms.

On supporting temporal quality of service in WDMA-based star-coupled optical networks

In this paper, we devise a preallocation-based single-hop wavelength division multiple access (WDMA) scheme to support temporal quality of service (QoS) in star-coupled optical networks, We consider a star-coupled broadcast-and-select network architecture in which N stations are connected to a star coupler with W different wavelength channels. Each of the W wavelength channels is slotted and shared by the !V stations by means of time division multiplexing. Depending on the tunability characteristics (tunable or fixed tuned) of the transmitters/receivers, we classify the network architecture as tunable transmitter/fixed tuned receiver (TT-FR), fixed tuned transmitter/tunable receiver (FT-TR), and tunable transmitter/tunable receiver (TT-TR). We first characterize each real-time message stream M/sub i/, with two parameters, the relative message deadline D/sub i/ and the maximum (total) message size C/sub i/ that can arrive within any time interval of length D/sub i/. We then discuss a restricted case in a TT-FR (or FT-TR) system in which the message streams from a source station are assumed to be all destined for the same destination station. Under this assumption, no source destination conflicts may occur. We propose a preallocation-based slot assignment scheme to preallocate slots to a set of isochronous message streams, (M/sub i/=(C/sub i/, D/sub i/)|1/spl les/i/spl les/n) in such a way that, in any time window of size D/sub i/ slots, at least C/sub i/ slots on a wavelength channel are allocated to M/sub i/ for all i. With the solution derived in the restricted case as a basis, we then consider slot assignment in a (general) TT-TR system and propose a binary splitting scheme to assign each message stream sufficient and well-spaced slots to fulfil its temporal requirement, subject to the source/destination conflict constraints. We rigorously prove the invariance properties, and the correctness, of the binary splitting scheme.

On supporting time-constrained communications in WDMA-based star-coupled optical networks

We devise a preallocation based single hop wavelength division multiple access (WDMA) scheme to support time constrained communication in star coupled optical networks. We consider a star coupled broadcast and select network architecture in which N stations are connected to a star coupler with W different wavelength channels. Each of the W wavelength channels is slotted and shared by the N stations by means of time division multiplexing. Networks with different transceiver configurations, i.e., TT-FR, FT-TR, and TT-TR systems, are investigated. We characterize each real time message stream M, with two parameters, relative message deadline D/sub i/ and maximum (total) message size C/sub i/ that can arrive within any time interval of length D/sub i/. We then discuss a restricted case in a TT-FR system in which the message streams from a source station are assumed to be all going to the same destination station. Under this assumption, no source/destination conflicts may occur. We propose a preallocation based slot assignment scheme to allocate slots to a set of isochronous message streams, {M/sub i/=(C/sub i/, D/sub i/))|1/spl les/i/spl les/n}, so that in any time window of size D/sub i/ slots, at least C/sub i/ slots on a wavelength channel are allocated to M/sub i/ for all i. With the solution derived in the restricted case as a basis, we then consider slot assignment in a (general) TT-TR system, and propose a binary splitting scheme to assign each message stream sufficient and well spaced slots to fulfill its timing requirement, subject to source/destination conflict constraints. We rigorously prove the invariant properties and the correctness of the binary splitting scheme.

Towards composable and extensible network simulation

In this paper, we present the design methodology, and the software architecture, of J-Sim, an open-source network simulation/emulation environment that has been developed, in part, under the support of the NSF next generation software program. We first give an overview of the component-based software architecture, called the autonomous component architecture (ACA), that is used as the underlying architecture for J-Sim. Then we describe how we lay a generalized packet-based network simulation framework, called extensible internetworking framework (INET), on top of ACA. Both the ACA and the INET have been implemented in Java. The resulting codes, along with an essential suite of network protocols and components (for the Internet best-effort/integrated services/differentiated services architecture) its extension for wireless and sensor networks, and a scripting framework and GUI interfaces, is called J-Sim. To demonstrate the composability and extensibility of J-Sim, we elaborate on how we model in J-Sim several different network architectures, namely the differentiated services (diffserv) architecture, the multiprotocol label switching (MPLS) architecture, and the wireless sensor network architecture.

A rate-based message scheduling paradigm

We propose a generic rate-based scheduling paradigm that can serve as a vehicle either for implementing existing well-known rate-based message scheduling algorithms, or for designing new rate-based message scheduling algorithms. The proposed scheduling paradigm is general enough to encompass a wide spectrum of rate-based scheduling algorithms and is flexible enough to allow realization of several desirable features, e.g., rate enforcement, capability of handling overbooking, and capability of providing rate parameters for traffic monitoring. Its modular design also facilitates realization of multiple scheduling algorithms in an uniform framework. Different levels of QoS can be provided to applications by invoking appropriate message schedulers implemented in the same framework. We demonstrate the use of the proposed scheduling paradigm by implementing the following two well-known families of message scheduling algorithms: (1) Virtual-Clock and its variations Self-Clocked Pair Queuing and Leap Forward Virtual Clock, and (2) Generalized Processor Sharing (or Weighted Fair Queuing) and its realistic implementations Packet-by-Packet Generalized Processor Sharing and Worst-case Fair Weighted Fair Queuing. We also design a simple message scheduling algorithm, called FIFO-r, using the paradigm, and derive analytically both the actual service rate and the end-to-end delay under FIFO-r.

On providing quality-of-service control for core-based multicast routing

In this paper, we develop efficient admission control tests for member join/leave and its associated state refresh and update procedures for receiver-initiated core-based multicast routing, e.g., core based tree (CBT) protocol, to allow construction of QoS-capable multicast trees, while making the minimum possible impact on the existing infrastructure. Specifically, we (i) derive sufficient conditions for a multicast tree to maintain its QoS; (ii) devise effective admission tests to verify whether or not a group member may join the multicast tree at adequate QoS, while not violating existing QoS guarantees to other on-tree members; and (iii) identify the minimum set of state information required for the admission tests and develop a soft state refresh and update procedure. Finally, we validate the effectiveness of the proposed mechanism by incorporating it into the CBT protocol, and evaluate it via event-driven simulations in terms of the probability of join requests being rejected, message overhead, and scalability.

A framework for provisioning of temporal QoS in core-based multicast routing

We develop and evaluate a set of member join/leave and state update/refresh procedures for QoS provisioning in core-based multicast routing with explicit member join and soft state refresh procedures. Specifically, in our prior work (Hung-Ying Tyan et al., 1999), we devised eligibility tests to verify whether or not a new member can join a multicast tree at adequate QoS while not violating the existing QoS guarantees to other on-tree members. We extend our prior work, identify the tradeoff between the amount of state kept at each on-tree router and the degree of collaboration among on-tree routers to conduct the tests, and develop two member join/leave procedures that range from using the most comprehensive state update procedure (and hence the least degree of collaboration among on-tree routers) to the other extreme. Also, we evaluate the proposed framework, in terms of the probability of locating feasible multicast trees, message overheads, and scalability.

Minimum initiation interval of multi-module recurrent signal processing algorithm realization with fixed communication delay

A novel iterative algorithm is proposed to compute the theoretical minimum initiation interval of a given recurrent algorithm when there is a known, fixed inter-module communication delay. Specifically, for a twin-module implementation problem, a novel representation called necessary initiation interval is introduced to facilitate the development of an iterative algorithm which yields both the minimum initiation interval and the corresponding cut set of the cyclic iterative computational dependence graph (ICDG). The convergence of this iterative algorithm in finite iterations is also proved.