Efficient distributed simulation of hierarchical DEVS models: transforming model structure into a non-hierarchical one
The Discrete Event Systems Specification (DEVS) formulism specifies a discrete event system in a hierarchical, modular form. This paper presents a distributed simulation methodology for models specified by the DEVS formalism. The methodology transforms a hierarchical DEVS model into a nonhierarchical one. This transformation can eliminate the overheads incurred during conventional hierarchical simulation, and make ease the synchronization of distributed simulation, thereby increasing the stability of the simulation engine. To show the effectiveness of the proposed methodology, we realize the simulation scheme in Visual C++, and conduct a benchmark simulation for a large-scale logistics system. The performance result shows that the proposed methodology works correctly and performs better than the previous approaches.

title: A Resilient Multipath Routing Protocol for Wireless Sensor Networks
abstract: Wireless sensor networks should be self-configuring, highly scalable, redundant, and robust in dealing with shifting topologies due to node failure and environment changes. The energy of a sensor node is the most important system resource, and one of the best ways of conserving energy is to distribute the routing load across all sensor nodes as much equally as possible. Considering the load balance for conserving energy, multipath routing protocols have been employed in sensor networks. In this paper we present a resilient multipath routing protocol based on AODV, named as RMRP, for wireless sensor networks. RMRP is an AODV-based multipath routing protocol in which sensor nodes setup double routing paths toward sink nodes in an AODV fashion and select one of them randomly for forwarding a packet. RMRP proposes a resilient route maintenance scheme which repairs broken links by utilizing localized information around neighbor nodes of the broken link, thereby reducing the flooding range of control messages. To show the effectiveness of the proposed route maintenance scheme, we evaluate the performance enhancement of the proposed scheme by ns2-based simulation.

title: A Web Services-Based Distributed Simulation Architecture for Hierarchical DEVS Models
abstract: The Discrete Event Systems Specification (DEVS) formalism specifies a discrete event system in a hierarchical, modular form. This paper presents a web-services-based distributed simulation architecture for DEVS models, named as DEVSCluster-WS. DEVSCluster-WS is actually an enhanced version of DEVSCluster by employing the web services technology, thereby retaining the advantages of the non-hierarchical distributed simulation compared to the previous hierarchical distributed simulations. By employing the web services technologies, it describes models by WSDL and utilizes SOAP and XML for inter-node communication. Due to the standardized nature of the web service technology, DEVSCluster-WS can effectively be embedded in the Internet without adhering to specific vendors and languages. To show the effectiveness of DEVSCluster-WS, we realize it in Visual C++ and SOAPToolkit, and conduct a benchmark simulation for a large-scale logistics system. We compare the performance of DEVSCluster-WS with DEVSCluster-MPI, the MPI-based implementation of DEVSCluster. The performance result shows that the proposed architecture works correctly and could achieve tolerable performance.

title: Design of a Service Discovery Architecture for Mobility-Supported Wired and Wireless Networks
abstract: Automatic service discovery will play an essential role in future network scenario and is an important component for MANET and collaboration in ubiquitous computing environment. This paper proposes a service discovery architecture, named as SLPA (Service Location Protocol based on AMAAM) in the mobility-supported wired and wireless environment of which the underlying protocol is AMAAM which is an aggregation-based Mobile IP implementation in MANET. In SLPA, the role of the directory agent is assigned to the mobility agent in AMAAM. The mobility agent periodically beacons an advertisement message which contains both the advertisement of the directory agent in SLP and the advertisement of the mobility agent in Mobile IP. For evaluating the functional correctness of SLPA and the overhead of maintaining a service directory in MANET, we simulate SLPA and analyze the overhead of control overheads for the aggregation. Through the simulation experiments, we investigate the functional correctness of the proposed architecture and analyze the control overheads of the aggregation.

title: CORBA-Based, Multi-threaded Distributed Simulation of Hierarchical DEVS Models: Transforming Model Structure into a Non-hierarchical One
abstract: The Discrete Event Systems Specification (DEVS) formalism specifies a discrete event system in a hierarchical, modular form. This paper presents DEVSCluster, a CORBA-Based, multi-threaded distributed simulation scheme for models specified by the DEVS formalism. The simulator transforms a hierarchical DEVS model into a non-hierarchical one. This transformation can ease the synchronization of the distributed simulation of DEVS models by enabling the transfer of events by direct remote method invocations, not explicit message transfers. By virtue of this feature, we can utilize CORBA for the event handling in DEVSCluster. To show the effectiveness of the proposed simulation scheme, we realize DEVSCluster in Visual C++, and conduct a benchmark simulation for a large-scale logistics system. We compare the performance of MPI and CORBA-based implementations. The performance result shows that the proposed methodology works correctly and performs better than the previous approaches.

title: Performance of Service Location Protocols in MANET Based on Reactive Routing Protocols
abstract: Automatic service discovery, the problem of discovering service providers by specifying desired properties of services, is an important and necessary component for collaboration in the ubiquitous computing environment such as MANET. This paper investigates the effects of the on-demand route discovery on the performance of service location protocols in MANET based on on-demand routing protocols. We first design a service discovery architecture in MANET based on AODV and evaluate both the distributed and centralized versions of the architecture by simulation. For evaluating the performance, we examine such performance metrics as service hit ratio, service discovery time, and control message overheads. The results show that the distributed scheme outperforms the centralized scheme in most simulation scenarios because of the on-demand routing overheads.

title: Background Updating for Visual Surveillance
abstract: Scene changes such as moved objects, parked vehicles, or opened/closed doors need to be carefully handled so that interesting foreground targets can be detected along with the short-term background layers created by those changes. A simple layered modeling technique is embedded into a codebook-based background subtraction algorithm to update a background model. In addition, important issues related to background updating for visual surveillance are discussed. Experimental results on surveillance examples, such as unloaded packages and unattended objects, are presented by showing those objects as short-term background layers.

title: Analysis of the competition between wired, DSL and wireless users in an access network
abstract: This paper analyzes the performance of a large population composed of several classes of long lived TCP flows experiencing packet losses due to random transmission errors and to congestion created by the sharing of a common tail-drop or RED bottleneck router. Each class has a different transmission error rate. This setting is used to analyze the competition between wired and wireless users in an access network, where one class (the wired class) has no or small (like BER in DSL) transmission error losses whereas the other class has higher transmission error losses, or the competition between DSL flows using different coding schemes. We propose a natural and simple model for the joint throughput evolution of several classes of TCP flows under such a mix of losses. Two types of random transmission error losses are considered: one where losses are Poisson and independent of the rate of the flow, and one where the losses are still Poisson but with an intensity that is proportional to the rate of the source. We show that the large population model where the population tends to infinity has a threshold (given in closed form) below which there are no congestion losses at all in steady state, and above which there is a stationary limiting regime in which we can compute both the mean value and the distribution of the rate obtained by each class of flow. We also show that the maximum mean value for the aggregated rate is achieved at the threshold.

title: Multicriteria Fuzzy Control Using Evolutionary Programming
abstract: In this paper, we propose a multicriteria fuzzy control (MFC) using evolutionary programming (EP) by which its λ-fuzzy measure is optimized. Basically the MFC is an extended version of the existing fuzzy logic controller to obtain the proper weights of the fuzzy rules for the fine tuning control. The MFC is designed by three steps: first, the attributes of the system output response are selected, second, the partial evaluations from the viewpoints of the attributes are assigned to the fuzzy rules, and third, the fuzzy integral is employed to aggregate the partial evaluation and the user's fuzzy measure about the consideration degree of each attribute for the proper weight value. EP is used to optimize the λ-fuzzy measure for the linear tuning property of the MFC. Computer simulations indicate that the proposed scheme has excellent performance.

title: TCP throughput analysis under transmission error and congestion losses
abstract: This paper analyzes the performance of a large population of long lived TCP flows experiencing random packet losses due to both random transmission errors and congestion created by the sharing of a common tail drop bottleneck router. We propose a natural and simple model for the joint throughput evolution of the set of TCP sessions under such a mix of losses. For the case of Poisson transmission errors, we show that the asymptotic model where the population tends to infinity leads to a well defined and tractable dynamical system. In particular, we get the mean value of the throughput of each session as a function of the transmission error rate and the synchronization rate in the bottleneck router. The large population asymptotic model has two interesting and non-intuitive properties: 1) there exists a positive threshold (given in closed form) on the transmission error rate above which there are no congestion losses at all in steady state; 2) below this threshold, the mean throughput of each flow is an increasing function of the transmission error rate, so that the maximum mean value is in fact achieved when the transmission error rate is equal to this threshold. The finite population model and models based on other classes of point processes are also studied. In particular, a sufficient condition is obtained for the existence of congestion times in the case of arbitrary transmission error point processes.

title: IP lookup by binary search on prefix length
abstract: Waldvogel et al.  have proposed a collection of hash tables (CHT) organization for an IP router table. IP lookup can be done with O(log l/sub dist/) hash-table searches, where l/sub dist/ is the number of distinct prefix-lengths (also equal to the number of hash tables in the CHT). Srinivasan and Varghese [ACM transactions on Computer Systems, Feb:1-40, 1999] have proposed the use of controlled prefix-expansion to reduce the value of l/sub dist/. The algorithm of [V. Srinivasan, 1999] does not minimize the storage required by the prefixes and markers for the resulting set of prefixes. We develop an algorithm that minimizes storage requirement but takes O(nW/sup 3/ + kW/sup 4/) time, where k is the desired number of distinct lengths, n is the number of prefixes, and W is the length of the longest prefix. Also, we propose improvements to the heuristic of [V. Srinivasan, 1999].