Spurred by technological advancements and consumer demands, the automotive industry is moving towards software-defined vehicles. To accommodate the complexities of software that execute on a system of networked ECUs (Electronic Control Units) and sensors, service-oriented architecture (SOA) becomes a viable architecture. SOME/IP (Scalable Service-Oriented MiddlewarE over IP) is a middleware standardized by AUTOSAR that implements SOA for automotive systems. By leveraging the unique features of the QUIC (Quick UDP Internet Connections) transport protocol, we design "Quick" SOME/IP by substituting the TCP used in SOME/IP with QUIC. In addition to supporting the four communications patterns offered by SOME/IP, Quick SOME/IP introduces fault tolerance streaming as the fifth communication pattern, which facilitates simultaneous data transmissions from one sender to one receiver over two physically disjoint paths to tolerate the failure of one path. Using the Nexus open-source C++ library implementation of QUIC, we modified vsomeip, an open-source C++ implementation of SOME/IP using TCP, to implement qsomeip. Our experiments demonstrated that qsomeip outperforms vsomeip in terms of reduced connection latency and enhanced security with the new capability of fault tolerant streaming.

Autonomous vehicles (AVs) present significant potential and challenges within transportation systems, necessitating sophisticated computational processes for perceiving environments, decision-making, and control. These processes, organized into AV pipelines, must operate under strict, dynamically varying deadlines to ensure safety and efficiency. Traditional software systems, such as those based on the Robot Operating System (ROS), struggle to manage these dynamic deadlines, often leading to either compromised performance or under-utilization of resources. The Dynamic Deadline-Driven (D3) Execution Model was developed to address these issues by centralizing deadline management and enabling AV systems to adapt computation in real-time based on environmental feedback. However, the D3 model lacks mechanisms for accurately predicting deadlines across diverse scenarios and handling extremely short response times required in emergencies. To address these issues, this paper integrates deep learning models within the D3 framework, enhancing its ability to set precise deadlines and respond effectively in critical situations. By deploying two deep neural network (DNN) models across different modules of the AV pipeline, the augmented system significantly improves safety, predictive accuracy, and latency minimization. Experimental analysis in the CARLA simulation environment demonstrates that the deep learning-enhanced D3 model outperforms traditional approaches, reducing collision rates and improving system responsiveness in long-distance driving and complex urban scenarios.

Managing urban traffic dynamics is critical in Intelligent Transportation Systems (ITS), where short-term traffic prediction is vital for effective congestion management and vehicle routing. While existing centralized deep learning (DL) models have achieved high prediction accuracy, their applicability is limited in decentralized ITS environments. The increasing use of connected vehicles and mobile sensors has led to decentralized data generation in ITS, presenting an opportunity to improve traffic prediction through collaborative machine learning. Recently, blockchain technology has shown promise in improving ITS efficiency, security, and reliability. In conjunction with blockchain, Federated Learning (FL) is a suitable approach to leverage online data streams in ITS; however, most research on FL for traffic prediction focuses on offline learning scenarios. This paper researches a blockchain-enhanced architecture for training online traffic prediction models using FL. The proposed approach enables decentralized model training at the edge of the ITS network, and extensive experiments used dynamically collected arterial traffic data shards as a case study to evaluate online learning performance. The results demonstrate that our online FL approach outperforms the per-device, non-federated baseline models for most sensors while maintaining a suitable execution time and latency for real-world deployment.

This paper presents a hybrid blockchain-edge architecture for managing Electronic Health Records (EHRs) with attribute-based cryptographic mechanisms. The architecture introduces a novel attribute-based signature aggregation (ABSA) scheme and multi-authority attribute-based encryption (MA-ABE) integrated with Paillier homomorphic encryption (HE) to protect patients’ anonymity and safeguard their EHRs. All the EHR activities and access control events are recorded permanently as blockchain transactions. We develop the ABSA module on Hyperledger Ursa cryptography library, MA-ABE module on OpenABE toolset, and blockchain network on Hyperledger Fabric. We measure the execution time of ABSA’s signing and verification functions, MA-ABE with different access policies and homomorphic encryption schemes, and compare the results with other existing blockchain-based EHR systems. We validate the access activities and authentication events recorded in blockchain transactions and evaluate the transaction throughput and latency using Hyperledger Caliper. The results show that the performance meets real-world scenarios’ requirements while safeguarding EHR and is robust against unauthorized retrievals.

Federated Learning (FL) is a privacy-preserving machine learning (ML) technology that enables collaborative training and learning of a global ML model based on aggregating distributed local model updates. However, security and privacy guarantees could be compromised due to malicious participants and the centralized FL server. This article proposed a bi-level blockchained architecture for secure federated learning-based traffic prediction. The bottom and top layer blockchain store the local model and global aggregated parameters accordingly, and the distributed homomorphic-encrypted federated averaging (DHFA) scheme addresses the secure computation problems. We propose the partial private key distribution protocol and a partially homomorphic encryption/decryption scheme to achieve the distributed privacy-preserving federated averaging model. We conduct extensive experiments to measure the running time of DHFA operations, quantify the read and write performance of the blockchain network, and elucidate the impacts of varying regional group sizes and model complexities on the resulting prediction accuracy for the online traffic flow prediction task. The results indicate that the proposed system can facilitate secure and decentralized federated learning for real-world traffic prediction tasks.

Accurate real-time traffic flow prediction can be leveraged to relieve traffic congestion and associated negative impacts. The existing centralized deep learning methodologies have demonstrated high prediction accuracy, but suffer from privacy concerns due to the sensitive nature of transportation data. Moreover, the emerging literature on traffic prediction by distributed learning approaches, including federated learning, primarily focuses on offline learning. This paper proposes BFRT, a blockchained federated learning architecture for online traffic flow prediction using real-time data and edge computing. The proposed approach provides privacy for the underlying data, while enabling decentralized model training in real-time at the Internet of Vehicles edge. We federate GRU and LSTM models and conduct extensive experiments with dynamically collected arterial traffic data shards. We prototype the proposed permissioned blockchain network on Hyperledger Fabric and perform extensive tests using virtual machines to simulate the edge nodes. Experimental results outperform the centralized models, highlighting the feasibility of our approach for facili-tating privacy-preserving and decentralized real-time traffic flow prediction.

Reliability and determinism are crucial to meet the requirements of real-time applications. The IEEE Time-Sensitive Networking (TSN) Task Group has introduced standards to facilitate the stringent timing requirements of TSN applications, which include IEEE 802.1Qbv (scheduling and traffic shaping) that helps enforce the computed transmission schedule. However, designing appropriate scheduling algorithms for TSN is left open. Owing to its high flexibility, many efforts have taken advantage of the centralized controller of TSN to build incremental end-to-end scheduling algorithms. Although these algorithms increase flexibility, they pose certain scheduling threats that could cause performance degradation or severe damage in certain real-time scenarios. In this paper, we discuss the threats of Denial of Scheduling and Blindness of Scheduler and evaluate their impacts based on the factors of attack intensity, attack start time, and attack strategy. Then, we propose a reactive solution to mitigate the effects of these threats.

With the increasing demand for advanced autonomous driving, the available communication resources may become constrained over different geographic areas. In addition, due to dynamic channel variations and imperfect cell deployments, guaranteeing the required communication resources for data hungry and delay-sensitive applications in autonomous vehicles (AVs), along their entire trips, becomes challenging. To address these issues, the paper investigates the feasibility of a hybrid system-optimum and user-equilibrium AV traffic framework subject to communication constraints, as well as its performance gain. Within such a framework, the paper introduces the problems of communication-constrained routing (CCR) and traffic control (CCTC) in the context of infrastructure-assisted autonomous driving and presents respective solutions. For CCR, an efficient two-layered routing scheme is proposed which can provide optimal trip duration. Simulation results show that the routing scheme achieves a good balance between longer duration of communication coverage and acceptable source-to-destination travel time. For CCTC, it is shown that there exists an optimal AV speed on each road segment, as well as an optimal inter-AV distance and an optimal number of AVs in each cell, to maximize the road-network AV throughput within a single cell. Moreover, spectrum allocation is used to achieve Pareto-optimal road-network throughput across cells, and a new key performance index (KPI) is defined to evaluate the traffic control capability of cellular systems. Simulation results validate the improvement of AV throughput via the proposed CCTC solution.

With children spending more time online, personal data are stored on their devices making them susceptible to online risks. Exposing students to cybersecurity education at an early age is critical for raising awareness and knowledge. Yet access to cybersecurity education curricular materials that are engaging for young students is limited. In this work, we present interactive cybersecurity stories for students in grades 3-5 delivered through a commercial social robot. Through focus groups and interviews we subsequently investigated teachers’ views on using a social robot for cybersecurity education, interest in incorporating social robots in the classroom, and perceptions of the ways in which social robots can impact teaching practice and student learning. Findings indicated that teachers found the social robot engaging and expressed interest in using it in their classroom despite some concerns. Findings have implications for the design and implementation of cybersecurity curricula delivered through emerging technologies.

With the shortage of cybersecurity professionals, there is a critical need to train more young-generation cybersecurity professionals to fill the gap. In this work, we designed interactive activities that make abstract cybersecurity concepts more tangible by using exciting new mixed reality (MR) technology to teach cybersecurity skills and raise the potential interest in cybersecurity careers for middle school students. We plan to analyze the immersive experience, situational interest, and workload after the experiment to study the participants' learning performance and user experience.

Industrial real-time applications demand their communication networks be robust and deterministic so that packets are delivered with bounded delay and jitter. The IEEE Time-Sensitive Networking (TSN) Task Group has amended the standards of IEEE 802.3 Ethernet to support time-triggered flows of real-time applications. However, the issues of routing and scheduling are left as open problems. Specifically, majority of the state-of-the-art scheduling efforts make certain assumptions, such as assuming that the routing information is known \textit{a priori} to focus on the scheduling problem or assuming that the information of flows is known in advance. Other studies that avoided these assumptions ignore certain valuable information that could be taken advantage of to make better routing decisions, such as the residual bandwidth. In this paper, we first propose an incremental QoS-aware path selection algorithm that uses QoS measurement to route TSN flows. Then, we introduce multiple incremental scheduling algorithms that address above mentioned issues, and demonstrate their performance.

Licensed-Assisted Access (LAA) is a promising technology to address the issues of ever-increasing traffic demands in cellular systems. However, the efficient coexistence of Wi-Fi and LAA in the same unlicensed spectrum raises many challenges. Most of the studies addressing this coexistence issue focus on a coexistent LAA and Wi-Fi network sharing a single carrier. In this paper, we investigate a coexistent network with multiple available carriers, which is the case for practical deployments. Specifically, we develop an efficient adaptive energy detection algorithm to avoid frequent collisions in coexistent Wi-Fi and LAA networks. moreover, a carrier selection algorithm, based on the LAA energy detection threshold, is proposed to further improve the coexistence performance. Simulation results validate the effectiveness of the proposed adaptive energy detection and carrier selection schemes.

In today's WLANs, scheduling of packet transmissions solely relies on the collision and success a station may experience. To better support traffic differentiation in dense WLANs, in this paper, we propose a distributed reservation mechanism for the Carrier Sense Multiple Access Extended Collision Avoidance (CSMA/ECA) MAC protocol, termed CSMA/ECA-DR, based on which stations can collaboratively achieve higher network performance. In addition, proper Contention Window (CW) will be chosen based on the instantaneously estimated number of active contenders in the network. Simulation results from dense scenarios with traffic differentiation demonstrate that CSMA/ECA-DR can greatly improve the efficiency of WLANs for traffic differentiation even with large numbers of contenders.

In wireless networks such as those based on IEEE 802.11, packet losses due to fading and interference are often misinterpreted as indications of congestion by the congestion control protocol at higher layers, causing an unnecessary decrease in the data sending rate. For delay-constrained applications such as video telephony, packet losses may result in excessive artifacts or freeze in the decoded video. We propose a simple and yet effective mechanism to detect and reduce channel-caused packet losses by adjusting the retry limit parameter of the IEEE 802.11 protocol while taking into account the delay requirement of the traffic. Since the retry limit is left configurable in the IEEE 802.11 standard and does not require cross-layer coordination, our scheme can be easily implemented and incrementally deployed. Experimental results of applying the proposed scheme to a WebRTC-based real-time video communication prototype show significant performance gain compared to the case where the retry limit is configured statically.

Two-tiered wireless sensor and actor networks (WSANs) have been proposed to enhance network capabilities, where a set of resource-rich mobile nodes (termed actors ) form a connected backbone to relay sensing data from static sensors to the sink and sometimes are requested by sensors to perform a particular action. Such a two-tiered WSAN facilitates scalability and can efficiently reduce the energy consumption incurred by conventional hop-by-hop relaying via only sensors. However, relocating actors to achieve both connectivity and load balance is a challenge, especially when there is no location information of the nodes. Connectivity ensures that the actors are connected, whereas load balance ensures that actors collect and originate a similar amount of sensory data from the sensors. In this article, we formulate the Connected and Balanced Mobile Actor Relocation (CBMAR) optimization problem to address both connectivity and load balance and prove that the problem is NP-hard. We thus propose a dual-mode distributed actor relocation protocol that does not rely on any location information of nodes to relocate actors. The idea is to locally form virtual Voronoi cells of actors (termed covering cells ) based on the lower-tiered topology, where each actor locally recruits its own sensor members to form its own covering cell. By maintaining the covering cell, each actor locally relocates itself toward a sensor along the lower-tiered topology. Extensive simulation results show that the protocol can achieve both objectives of connectivity and load balance with low moving and communication overheads.

In wireless networks such as those based on IEEE 802.11, packet losses due to fading and interference are often misinterpreted as indications of congestion, causing unnecessary decrease in the data sending rate due to congestion control at higher layer protocols. For delay-constrained applications such as video teleconferencing, packet losses may result in excessive artifacts or freeze in the decoded video. We propose a simple and yet effective mechanism to detect and reduce channel-caused packet losses by adjusting the retry limit parameter of the IEEE 802.11 protocol. Since retry limit is left configurable in the IEEE 802.11 standard, and does not require cross-layer coordination, our scheme can be easily implemented and incrementally deployed. Experimental results of applying the proposed scheme to a WebRTC-based realtime video communication prototype show significant performance gain compared to the case where retry limit is configured statically.

The increasing popularity of Internet-capable mobile devices leads to the explosion of mobile data traffic. Although the emerging mobile broadband systems such as 4G LTE promise higher bandwidth and lower latency for video traffic, it is not power efficient to deliver video traffic over cellular networks. This paper studies how peer-to-peer communications via wireless local networks could complement the cellular networks so as to minimize the power consumption of mobile devices. Specifically, we consider the scenario in which a group of nearby mobile devices share the streaming contents, originated from the cellular networks, over the wireless local area networks in a peer-to-peer manner. We focus on investigating how the mobile devices should cooperate to minimize their own power consumption. The problem has been formulated into a linear programming (LP) model, and numerical results show that at least 31% of the power consumption can be saved on mobile devices through the cooperation among them.

Small-cell networks have been proposed to meet the demand of ever growing mobile data traffic. One of the prominent challenges faced by small-cell networks is the lack of sufficient backhaul capacity to connect small-cell base stations (small-BSs) to the core network. We exploit the effective application layer semantics of both spatial and temporal locality to reduce the backhaul traffic. Specifically, we envision that small-BSs are equipped with storage facility to cache contents requested by users. As the cache hit ratio increases, most of the users' requests can be satisfied locally without incurring traffic over the backhaul. To make informed caching decisions, the mobility patterns of users must be carefully considered as users might frequently migrate from one small cell to another. We study the issue of mobility-aware content caching, which is formulated into an optimization problem with the objective to maximize the caching utility. As the problem is NP-complete, we develop a polynomial-time heuristic solution termed MobiCacher with bounded approximation ratio. We conduct trace-based simulations to evaluate the performance of MobiCacher, which show that MobiCacher yields better caching utility than existing solutions.

The existing dynamic spectrum access network architecture fails to offer incentives to primary users (PUs). Therefore, PUs are unwilling to cooperate with secondary users (SUs) and intend to set up stringent requirements on SUs' spectrum access. This diminishes the benefit of dynamic spectrum access and hinders its commercialization success. In this paper, we propose a novel architecture for dynamic spectrum access networks, termed incentivized cooperative dynamic spectrum access network (IC-DSAN), to motivate PUs to cooperate with SUs, such that both PUs and SUs achieve significantly higher performance. In an IC-DSAN, SU nodes serve as relays between PU nodes and while relaying PU packets, utilize network coding to encode SU packets onto PU packets, i.e., SU packets get a `free ride' via network coding. To further improve the performance, we propose a new network coding scheme termed coding over coded packets. At last, an optimization model is developed to analyze the throughput gain of IC-DSAN. The performance evaluation indicates that the throughputs of both PUs and SUs significantly increase.

ABSTRACT Constrained by the physical environments, thelong‐thintopology has recently been promoted for many practical deployments of wireless sensor networks (WSNs). In general, a long‐thin topology is composed of a number of long branches of sensor nodes, where along a branch each sensor node has only one potential parent node toward the sink node. Although data aggregation may alleviate excessive packet contention, the maximum payload size of a packet and the dynamically changing traffic loads may severely affect the amount of sensor readings that may be collected along a long branch of sensor nodes. In addition, many practical applications of long‐thin WSNs demand the exact sensor readings at each location along the deployment areas for monitoring and analysis purposes, so sensor readings may not be aggregated when they are collected. This paper proposes a lightweight, self‐adaptive scheme that designates multiple collection nodes, termedlock gates, along a long‐thin network to collect sensor readings sent from their respective upstream sensor nodes. The self‐adaptive lock gate designation scheme balances between the responsiveness and the congestion of data collection while mitigating the funneling effect. The scheme also dynamically adapts the designation of lock gates to accommodate the time‐varying sensor reading generation rates of different sensor nodes. A testbed of 100 Jennic sensor nodes is developed to demonstrate the effectiveness of the proposed lock gate designation scheme. Copyright © 2011 John Wiley & Sons, Ltd.

Using the technology of wireless energy transfer, the paper proposes Qi-ferry which physically carries energy, roves a wireless sensor network, and wirelessly charges sensor nodes to extend their lifetime. To optimize the usage of the entire energy reserve on a Qi-ferry, both the movement of the Qi-ferry itself and its wireless charging of sensor nodes share the same pool of battery energy reserve, resulting in a tradeoff between how many sensors the Qi-ferry could charge and how far it could travel. The paper formulates an energy-constrained Qi-ferry wireless charging problem in wireless sensor networks, which maximizes the number of sensors wirelessly charged by a Qi-ferry subject to an energy constraint limiting the total energy consumed by the Qi-ferry for both moving and charging. Due to the NP-hardness of the problem, the paper proposes heuristic solutions based on the meta-heuristics of Particle Swarm Optimization. Evaluation results validate the effectiveness of the solutions.

The overlay approach to dynamic spectrum access recently proposed in information theory allows both primary users (PUs) and secondary users (SUs) to simultaneously access the same spectrum with comparable power levels. However, the information theory approach is based on idealized assumptions that are difficult to be satisfied in practice. We propose a practical scheme with the overlay flavor for multi-hop wireless networks subject to two challenging design constraints: (1) PUs can not be modified, and (2) the performance of PUs can not degrade. Using the notion of credit in our scheme, SUs first help with the traffic delivery for PUs, and in return SUs later are allowed to access the spectrum in a manner disruptive to PUs. Specifically, SUs earn credit for helping PUs and consume credit for disrupting PUs. Moreover, we propose a distributed credit diffusion algorithm for SUs to share credit, and we modify a widely used reactive routing protocol to satisfy the design constraints. This overlay scheme is then integrated with the widely used interweave scheme to form the Credit-based Overlay and Interweave (CONI) protocol. Simulation results show that CONI can significantly benefit both PUs and SUs.

In this paper, we present a rendezvous scheme for dynamic spectrum access (DSA) networks that can achieve approximately optimal throughput while not relying on a common control channel. Compared with existing rendezvous schemes for DSA networks that use a common control channel, the proposed scheme avoids congestion and jamming of the control channel, and also reduces control complexity and overhead in DSA. We prove that the proposed rendezvous scheme achieves approximately optimal throughput, and analyze the convergence time of this scheme to obtain the approximately optimal throughput.

Underwater acoustic networks (UWANs) have emerged as the primary tool to monitor and act upon the well-being of marine environment. However, the significantly slower propagation speed of acoustic signals, in contrast to RF signals, introduces the spatio-temporal uncertainty, which makes existing medium access control (MAC) solutions for terrestrial RF wireless networks unsuitable for UWANs. In this paper, we investigate transmission scheduling for time-based MAC protocols and design scheduling algorithms that take advantage of the long propagation delay of acoustic signals to facilitate concurrent transmissions and receptions of acoustic communications. Specifically, we specify the constraints that MAC protocols need to satisfy to avoid conflicts and model these constrains into a Mixed Integer Linear Programming model. We also design heuristics that compute conflict-free transmission schedules, and demonstrate via simulation that the heuristics significantly improve network throughput.

Cooperative transmissions combat various fading effects in wireless communications by employing multiple antennas from different nodes to achieve spatial diversity. Virtual Multiple-Input Single-Output (MISO) is one instance of cooperative transmissions capable of achieving higher receiving SNR, which can either extend the transmission range or increase the transmission rate. While the physical layer performance of Virtual MISO has been well studied, this paper describes the Cooperative Source Routing (CSR) protocol to convert physical layer gain into network level performance improvement. With both route request and route reply control packets being transmitted cooperatively, CSR can explore routes with high cooperative diversity. We demonstrate CSR's performance through simulation and compare CSR with other protocols.

Geographic routing is a scalable routing scheme for wireless networks, where nodes make local routing decisions using position information. Cooperative transmissions utilize spatial diversity to combat fading in wireless channels. In this paper, we incorporate cooperative transmissions into geographic routing, and propose the Location-Aware Cooperative Routing (LACR). In LACR, a node that receives Route Request (RREQ) makes an individual decision on whether and how to rebroadcast RREQ based on its position and capability to cooperate. A theoretical analysis of the impact of cooperative transmissions on the transmission range extension is presented to guide the measurement of the potential performance of each node. Through simulation, we show that LACR performs better in terms of higher probability to find a route and higher throughput in comparison to Single-Input-Single-Output (SISO) based routing protocol.

In dynamic spectrum access (DSA), secondary users (SUs) dynamically search and access spectrum bands unused by primary users to communicate. We propose a DSA scheme where it does not require a control channel for coordination and SU nodes do not need to exchange control messages to rendezvous. Every SU node selects its operational channel independently. When a node wants to rendezvous with another node, the former estimates the operational channel of the latter. The scheme ensures that such rendezvous has a high probability of success, while operational channels are diversified to reduce co-channel interference and hence increase throughput. We develop a mathematical model to analyze the performance of the scheme. Both analytical and simulation results show that the scheme achieves very good performance.

The dynamic spectrum access (DSA) capability of cognitive radio networks (CRN) promises to resolve both the spectrum scarcity and the low spectrum utilization problems caused by today's static spectrum access (SSA) policy. With DSA, CRN nodes search the dynamically accessible spectrum bands for communication. In this paper, we study a random DSA scheme, where each node randomly selects its operating band based on the locally detected accessible spectrum bands. This scheme does not need the coordination or exchange of control messages to select a communication band between a sender and a receiver, and is desirable in certain scenarios. We analyze the performance of this random DSA scheme. Numerical results show that the random DSA scheme can achieve 60% of the theoretical maximum performance.

Dynamic spectrum access (DSA) promises to resolve spectrum scarcity and low spectrum utilization caused by today's static spectrum access (SSA) policy. In DSA, secondary users dynamically search and access spectrum bands that are temporarily unused by primary users. In this paper, we propose a control-free DSA algorithm for cognitive radio networks (CRN). Our algorithm enables each CRN node to select its operation band without coordination and exchange of control messages with neighbors. The contribution of our algorithm is that such an independently selected band can reach neighbors with high probability, while streamlining control complexity and overhead in DSA. We develop an analytical model to evaluate performance. Numerical results show that our control-free DSA algorithm can achieve very good performance.

For underwater wireless sensor networks (UWSNs), data muling is an effective approach to extending network coverage and lifetime. Sensor data are collected when a mobile data mule travels within the wireless communication range of the sensor. Given the constrained energy available on a data mule and the energy consumption of its communications and movement operations, a data mule may be prevented from visiting every deployed sensor in a tour. We formulate the tour planning of a data mule collecting sensor data in UWSNs as an energy-constrained bi-objective optimization problem termed the Underwater Data Muling Problem (UDMP). UDMP has the two conflicting objectives of minimizing the length of a tour and maximizing the number of sensors contacted, while satisfying the energy constraint of the data mule at all times. We design an approximation algorithm to solve one special case of this NP-hard problem, which computes a set of Pareto-efficient solutions addressing the tradeoff between the two optimization objectives so as to make proper tour planning. Simulation results validate the effectiveness of this algorithm..

Existing work on placing additional relay nodes in wireless sensor networks to improve network connectivity typically assumes homogeneous wireless sensor nodes with an identical transmission radius. In contrast, this paper addresses the problem of deploying relay nodes to provide fault tolerance with higher network connectivity in heterogeneous wireless sensor networks, where sensor nodes possess different transmission radii. Depending on the level of desired fault tolerance, such problems can be categorized as: 1) full fault-tolerant relay node placement, which aims to deploy a minimum number of relay nodes to establish k(k ? 1) vertexdisjoint paths between every pair of sensor and/or relay nodes and 2) partial fault-tolerant relay node placement, which aims to deploy a minimum number of relay nodes to establish k(k ? 1) vertex-disjoint paths only between every pair of sensor nodes. Due to the different transmission radii of sensor nodes, these problems are further complicated by the existence of two different kinds of communication paths in heterogeneous wireless sensor networks, namely, two-way paths, along which wireless communications exist in both directions; and one-way paths, along which wireless communications exist in only one direction. Assuming that sensor nodes have different transmission radii, while relay nodes use the same transmission radius, this paper comprehensively analyzes the range of problems introduced by the different levels of fault tolerance (full or partial) coupled with the different types of path (one-way or two-way). Since each of these problems is NP-hard, we develop O(?k2)-approximation algorithms for both one-way and two-way partial fault-tolerant relay node placement, as well as O(?k3)-approximation algorithms for both one-way and two-way full fault-tolerant relay node placement (? is the best performance ratio of existing approximation algorithms for finding a minimum k-vertex connected spanning graph). To facilitate the applications in higher dimensions, we also extend these algorithms and derive their performance ratios in d-dimensional heterogeneous wireless sensor networks (d ? 3). Finally, heuristic implementations of these algorithms are evaluated via QualNet simulations.

A transport layer protocol supporting multihoming allows an application to transmit data via multiple paths simultaneously (termed concurrent multipath transfer, or CMT for short). SCTP is an IETF-supported transport layer protocol with built-in multihoming capability. Earlier work by Iyengar et. al.proposed a CMT protocol using SCTP multihoming for improving application throughput, which studied the performance of CMT over wired networks using ns-2 simulations. Given recent advances in multiple radio nodes, multichannel radios, and multipath routing we believe that we will see more multihomednodes in the wireless networks context. This motivates us to study theSCTP-based CMT over wireless networks. In this paper, we investigate the throughput of the applications using the SCTP-based CMT over IEEE 802.11 static multihop wireless networks with QualNet simulations.

In contrast to existing work on the connected coverage problem in wireless sensor networks which assumes omnidirectional sensors with disk-like sensing range, this paper investigates a suite of novel problems related to connected coverage in directional sensor networks where sensors only sense directionally and have a sector-like sensing range. We first consider the problems of deploying a minimum number of directional sensors to form a connected network to cover either a set of point- locations (connected point-coverage deployment (CPD)) or the entire target sensing area (connected region-coverage deployment (CRD)). CPD is NP-hard as its subproblem of geometric sector cover (GSC) is NP-hard. We present two approximation algorithms for GSC as subroutines, and develop a general solution framework for CPD with approximation ratio sigma + O(1), where sigma is the approximation ratio of the selected GSC subroutine. We also describe two efficient deployment patterns with guaranteed covering density for CRD, and analyze their performance bounds with respect to arbitrary non-crossing deployment patterns. Extensive simulation results validate the correctness and merits of the presented algorithms and analysis.

This paper describes CEDAR, a unicast routing protocol that balances transmission power and hop count in ad hoc networks. The protocol adopts the mechanism of swarm intelligence to dynamically assign transmission power to nodes along the discovered route (to reduce the sum of transmission power) subject to an end-to-end hop count constraint in data delivery. Simulation results validated the effectiveness of the protocol, and demonstrated the tradeoff relationship between end-to-end total transmission power and hop count.

The minimum-energy multicast tree problem aims to construct a multicast tree rooted at the source node and spanning all the destination nodes such that the sum of transmission power at non-leaf nodes is minimized. However, aggressive power assignment at non-leaf nodes, although conserving more energy, results in multicast trees that suffer from higher hop count and jeopardizes delay-sensitive applications, signifying a clear tradeoff between energy efficiency and delay. This article formulates these issues as a constrained Steiner tree problem, and describes a distributed constrained Steiner tree algorithm, which jointly conserves energy and bounds delay for multicast routing in ad hoc networks. In particular, the proposed algorithm concurrently constructs a constrained Steiner tree, performs transmission power assignment at non-leaf nodes, and strives to minimize the sum of transmission power of non-leaf nodes, subject to the given maximum hop count constraint. Simulation results validate the effectiveness and reveal the characteristics of the proposed algorithm.

A publish/subscribe system consists of publishers, subscribers, and a delivery infrastructure, where publishers produce events, subscribers declare their interests in receiving events via subscriptions, and the delivery infrastructure forwards subscribed events from publishers to corresponding subscribers. The paper describes a distributed, subscription-aware publish/subscribe tree (PST) construction protocol, termed DSAPST, for MANET. DSAPST specifically takes subscribers' subscriptions into account so that subscribers sharing common subscriptions that are closer in terms of hop count would be connected together in the constructed PSTs, resulting in lower event delivery overhead in terms of the number of wireless transmissions. In addition, DSAPST adapts to mobility of nodes, allows existing nodes to join and leave as subscribers, and accommodates brand new nodes joining a MANET as subscribers. Simulation results show that DSAPST outperforms a MAODV-based PST construction protocol which is not subscription-aware.

Existing work on placing additional relay nodes in wireless sensor networks to improve network connectivity typically assumes homogeneous wireless sensor nodes with an identical transmission radius. In contrast, this paper addresses the problem of deploying relay nodes to provide fault-tolerance with higher network connectivity in heterogeneous wireless sensor networks, where sensor nodes possess different transmission radii. Depending on the level of desired fault-tolerance, such problems can be categorized as: (1) full fault-tolerance relay node placement, which aims to deploy a minimum number of relay nodes to establish k (k ges 1) vertex-disjoint paths between every pair of sensor and/or relay nodes; (2) partial fault-tolerance relay node placement, which aims to deploy a minimum number of relay nodes to establish k (k ges 1) vertex-disjoint paths only between every pair of sensor nodes. Due to the different transmission radii of sensor nodes, these problems are further complicated by the existence of two different kinds of communication paths in heterogeneous wireless sensor networks, namely two-way paths, along which wireless communications exist in both directions; and one-way paths, along which wireless communications exist in only one direction. Assuming that sensor nodes have different transmission radii, while relay nodes use the same transmission radius, this paper comprehensively analyzes the range of problems introduced by the different levels of fault-tolerance (full or partial) coupled with the different types of path (one-way or two-way). Since each of these problems is NP-hard, we develop O(sigmak2)-approximation algorithms for both one-way and two-way partial fault-tolerance relay node placement, as well as O(sigmak3)-approximation algorithms for both one-way and two-way full fault-tolerance relay node placement (sigma is the best performance ratio of existing approximation algorithms for finding a minimum k-vertex connected spanning graph). To facilitate the applications in higher dimensions, we also extend these algorithms and derive their performance ratios in d-dimensional heterogeneous wireless sensor networks (d ges 3). Finally, heuristic implementations of these algorithms are evaluated via simulations.

Past research studying the operations of TCP over wireless/mobile ad hoc networks has shown that TCP cannot be adopted as-is for use in mobile ad hoc networks (MANET) to achieve reasonable performance. This is because the assumptions made during designing TCP were made to make TCP work for wired networks, not MANETs. Consequently, most past research evaluating the performance of MANET routing protocols has concentrated on using CBR traffic over UDP for evaluation. In this paper, we distinguish practical use of TCP from use of TCP for evaluation purposes, and examine whether using TCP as an evaluation tool to evaluate MANET routing protocols will yield any new insights, even though we readily agree with past research that using TCP as-is (that is, as packaged for wired networks) for practical use over MANET is not a good approach. We motivated this idea because even though TCP does not function well over MANET, the fundamental expectations TCP has over the network are "universal" metrics which MANET researchers should strive for as well.Using simulations, we show that by studying the performance of MANET routing protocols using TCP traffic, we obtain a different understanding of the protocols studied, and this understanding cannot be obtained via applying CBR/UDP traffic. In this spirit, we urge MANET routing protocol designers to use TCP as an evaluation tool during the protocol design process.

In recent years, a number of P2P systems, for instance, Gnutella, KaZaA, Napster, and BitTorrent, have been proposed for the wired Internet. However, these protocols are not immediately applicable to the mobile ad hoc networks (MANETs) owing to the extreme conditions MANETs operate under. Of the above protocols, although BitTorrent has several features which make it an ideal candidate for adapting to MANETs, the current specification of BitTorrent has several drawbacks which make a straightforward implementation of BitTorrent for MANETs an undesirable solution. In this paper, we investigate a straightforward implementation of BitTorrent in MANETs, termed BTI, and compare its performance with a cross-layer adaptation of BitTorrent for MANETs, termed BTM. We resolve the issues of centralized control and single point of failure in BTI by proposing mechanisms to decentralize the BitTorrent model for MANETs and provide resource/data redundancy to improve the protocol performance. In addition, the cross-layer model of BTM is more suited for use in a MANET. Our performance comparison studies show that BTM is able to outperform BTI in terms of goodput, and the number of pieces delivered, in the context of amortizing the client download expenses over more connections (that is, BTM has a higher average peer degree)

Most existing topology control algorithms for heterogeneous mobile ad hoc networks (H-MANETs) only consider non-uniform transmission power (range) and use the Euclidean distance as their metrics for topology creation. However, in practice, communication capability could be diverse not only in the maximum transmission power (range), but also in the threshold receiving power. We present a localized topology control algorithms for H-MANETs termed Topology Control with Power Estimation (TCPE). By using the technique of power estimation, TCPE directly collects the minimum transmission power among nodes for topology control without requiring any location, angle-of-arrival, or global topology information. TCPE preserves the network connectivity and greatly improves the spatial reuse and power efficiency. TCPE also includes a topology maintenance mechanism to address mobility. Simulation results demonstrate the merits of TCPE.

In traditional MANET MAC and routing protocols, if any link in a route fails, multiple fruitless attempts are made to use the failed link before reporting failure to the routing layer or attempting local recovery. The high frequency of link errors between mobile nodes requires rapid recovery in order to provide acceptable performance, especially for real-time applications. In this paper, we propose CIFLER, a cross-layer approach which uses enhanced channel reservation messages to allow alternate nodes to immediately elect themselves using only inferred neighbor information. This self-election avoids reliance on individual links and minimizes the impact frequent link errors have on delay, energy usage, and the function of upper layer protocols. We show via simulation that CIFLER provides better results in typical MANET scenarios. Unlike other local recovery schemes, CIFLER does not suffer from duplicated messages, allows new nodes to almost immediately learn the information needed to assist in the recovery of existing routes, and does not require additional hardware, delays, or control messages

This paper proposes a new approach that applies multibeam directional antennas to controlling topology by reducing the power intensity directionally instead of omnidirectionally. In contrast to omnidirectional topology control, which reduces transmission power (and, thus, the resulting transmission range) in all directions, the proposed approach maintains the original power range in certain directions while clearing the power intensity in other directions. This paper shows that the proposed approach and the. omnidirectional topology control approach are equivalent in terms of the probability distribution of the number of symmetric neighbors in their resulting topologies. Major benefits of this approach include reduced and steady hop count, power saving independent of the number of neighbors within the original power range, and symmetric link in terms of SNR quality, as compared to omnidirectional topology control approaches. Simulation studies have demonstrated these benefits and highlighted its trade-offs.

For mobile ad hoc networks, network-wide broadcast is a critical network layer function supporting route discovery and maintenance in many unicast and multicast protocols. A number of broadcast schemes have been proposed; however, almost all of them assume the usage of omnidirectional antennas and focus on broadcast overhead in terms of the number of forwarding nodes. Directional antennas have narrow beams and can potentially reduce broadcast overhead in terms of the ratio of the number of received duplicate packets to the number of nodes that receive broadcast packets. In this paper, we propose to map probability-based directional and omnidirectional broadcast to bond and site percolation, respectively, and describe a collection of directional antenna-based broadcast schemes for mobile ad hoc networks. A thorough and comparative simulation study is conducted to demonstrate the efficiency of the proposed schemes.

Mobile access points with long range communication capability may be deployed in mobile ad hoc networks to bridge (e.g. via airborne units) network partitions. In this paper, we address the problem of continuously navigating mobile access points to proper locations within their respective partitions such that certain network performance metrics are optimized, and refer to this problem as trajectory control. We present several trajectory control algorithms with different assumptions on locationing capabilities to achieve the objectives of reducing hop count and reducing overhead. Our proposed algorithms are more practical than existing centralized algorithms and make fewer assumptions on locationing capabilities. Simulation results demonstrate the effectiveness of the proposed algorithms.

The paper describes a distributed energy-conserving multicast routing protocol, termed ECMANSI, which makes use of the biological metaphor of swarm intelligence to create the multicast structure. ECMANSI adopts a core-based approach by establishing connectivity among the group members through a designated core node. Each node explores a better path with lesser transmission power to the core, which results in an energy efficient multicast structure. Results from extensive simulations have validated the efficiency of the protocol.

Delay tolerant mobile networks are characterized by the possible non-existence of end-to-end paths. For instance, environmental factors and energy constraints in mobile ad hoc and wireless sensor networks make the preservation of end-to-end connectivity challenging. To overcome the problem, the "store-carry-and-forward" (SCF) paradigm has been proposed, where mobile nodes may physically carry and transport messages between nodes to facilitate eventual message delivery. We propose a suite of autonomous and dynamic SCF algorithms, together called pickup and delivery (PAD) Routing, which adapt the traditional algorithmic vehicle routing problem (VRP) and covering tour problem (CTP) to the context of delay tolerant mobile networks. The objectives of PAD routing are to reduce the message transport delay and to increase the delivery ratio in the presence of network partitions. Simulation results demonstrate the efficiency of these algorithms.

We propose a quorum-based approach to facilitating match-making (content-based routing) service for wireless mesh networks. Given a wireless mesh network, mesh nodes first autonomously select a set of backbone nodes via a backbone selection protocol. These backbone nodes then participate in a symmetric coterie construction process to create a quorum system. A quorum system has the property that the interaction of every two quorums is not empty and the union of all quorums results in the set of all backbone nodes. By using these two properties, the approach facilitates a match-making service that matches producer nodes' advertisements and consumer nodes' subscriptions at intersecting nodes between quorums.

This paper addresses the issue of improving packet delivery for multicast in mobile, ad hoc networks and proposes a reliability improvement mechanism called protocol-independent packet delivery improvement service (PIDIS) to recover lost packets. PIDIS is a non-persistent, best-effort reliability improvement service that exploits the mechanism of swarm intelligence to make intelligent decisions about whence to fetch the lost packets. PIDIS employs the beneficial aspects of probabilistic routing and adapts well to mobility. PIDIS achieves probabilistic reliability and, unlike other gossip-based schemes, does not need to maintain information about group members from which lost packets are retrieved. Further PIDIS does not rely on any underlying routing protocol or primitive, and can be incorporated into any (unreliable) ad hoc multicast routing protocol. Lastly, because PIDIS is non-persistent, it does not incur any overhead when there is no lost message to be recovered. We incorporated PIDIS into ODMRP, and compared it against anonymous gossip (AG) implemented over ODMRP, and ODMRP. Our simulation results show that PIDIS+ODMRP in most cases, is more efficient and performs better than AG+ODMRP and ODMRP in terms of packet delivery, end-to-end delay and MAC layer overheads. We attribute the better performance and lower MAC overheads of PIDIS+ODMRP to the efficient gossiping made possible by using swarm intelligence techniques.

Wc propose two efficient search schemes that use query messages filtering/gossiping and adaptive hop-limited search, respectively, for peer-to-peer (P2P) file sharing over mobile ad hoc networks. While the former does network-wide flooding of query messages and is suitable for the applications requiring file update, the latter uses local broadcast transmission and exploits the degree of replication. We compare the first scheme with a Gnutella-like P2P file sharing system [T. Klingberg and R. Manfredi, 2002] in a MANET environment via simulation, and show that the proposed schemes offers less transmission overhead and better scalability. We also qualitatively compare both proposed schemes with ORION [A. Klemm et al., Mar. 2003].

This paper presents a new approach using directional antenna to controlling topology by reducing the power intensity directionally instead of omnidirectionally. In particular, the approach maintains the original power range in certain directions while making it (totally) cleared in others. Its major benefits include lower hop count, power saving independent of the number of neighbors within the original power range, and symmetric link in terms of SNR quality, as compared to other approaches. We have shown the similar capability of this approach to existing omnidirectional approaches in terms of maintaining network connectivity. We have also explained the approach's phase transitional behavior in terms of network connectivity using the percolation theory. Simulations are conducted to demonstrate its benefits and tradeoffs.

The topology of an ad hoc network has a significant impact on its performance in that a dense topology may induce high interference and low capacity, while a sparse topology is vulnerable to link failure and network partitioning. Topology control aims to maintain a topology that optimizes network performance while minimizing energy consumption. Existing topology control algorithms utilize either a purely centralized or a purely distributed approach. A centralized approach, although able to achieve strong connectivity (k-connectivity for k /spl ges/ 2), suffers from scalability problems. In contrast, a distributed approach, although scalable, lacks strong connectivity guarantees. We propose a hybrid topology control framework, cluster-based topology control (CLTC) that achieves both scalability and strong connectivity. By varying the algorithms utilized in each of the three phases of the framework, a variety of optimization objectives and topological properties can be achieved. In this paper, we present the CLTC framework; describe topology control algorithms based on CLTC and prove that k-connectivity is achieved using those algorithms; analyze the message complexity of an implementation of CLTC, namely, CLTC-A, and present simulation studies that evaluate the effectiveness of CLTC-A for a range of networks.

In this paper, we describe a transport layer mobility scheme termed Cellular SCTP, or cSCTP for short, based on the stream control transmission protocol (SCTP), for seamless soft handoff. We compare mobile IPv6 and two of its variants (mobile IPv6 with fast-handover and hierarchical mobile IPv6) with cSCTP on various aspects (especially the handoff process of micro-mobility). We also analyze the mobile IPv6 handover mechanism in detail to reveal the operations that constitutes extra delays or packet losses caused by handoffs. Furthermore, we describe the interworking of cSCTP with SIP for mobility management.

This paper investigates the benefits and impacts of using directional antennas for multicast communications in ad hoc networks. In terms of signal reception, directional antennas have shown considerable improvement in the performance of all aspects over omni-directional antennas, especially over dense networks with heavy traffic load. In addition, we have found that transmitting multicast packets directionally to known neighboring group members or forwarders can help reduce the average end-to-end packet delay and increase the overall throughput. However, directional transmission of unacknowledged data transfers may result in lower performance in terms of packet delivery ratio than omni-directional transmission in any carrier sensing MAC protocols under moderate load due to the effect from the hidden terminal problem. Both analytical results and simulation results, as well as an acknowledgment mechanism to improve the successful delivery rate of multicast data packets, are presented.

Nodes in ad hoc networks typically rely on battery energy. The wireless interface is one of the major drain on energy reserves of the nodes. Turning off network interfaces of idle nodes while maintaining effective network forwarding capacity is an effective energy conservation technique. In this paper, we describe the ant-based energy conservation (ABEC) mechanism to prolong network lifetime. By imitating the pheromom trail laying and following behavior of biological ants, ABEC allows nodes to alter the forwarding behavior of ant packets to control pheromone trail concentration when energy consumption needs to be reduced. These nodes safely turn off network interfaces while other nodes maintain pheromone trails to preserve network coverage and forwarding performance. We present the details of ABEC and evaluate its performance when it collaborates with AODV and an ant-based routing protocol. The results show that in comparison to AODV, ABEC successfully extends network lifetime by a factor of 2 to 3, while only slightly reducing network forwarding performance.

Energy drainage from a node is mainly caused by the power consumption of the nodes communication device. A MAC protocol is the main mechanism to provide efficient access to the shared wireless channel. Directional antennas provide several benefits over several omnidirectional ones including the reduced energy consumption in frame transmissions. In this paper, we study and compare different generic directional virtual carrier sensing schemes (i.e., directional-RTS/CTS) in terms of their energy efficiency and performance. Both analytical and simulation results show that the schemes using directional-RTS and/or directional-CTS are more energy efficient than other schemes.

Traditional MAC protocols used in ad hoc networks employ omnidirectional antennas. Directional antennas have emerged as an alternative due to their capability of spatial reuse, low probability of detection, robustness to jamming, and other beneficial features. We conducted a comparison study of existing directional and omnidirectional MAC protocols by contrasting their features and evaluating their performance under various network load and topology. Specifically we presented rationale for the better performance of some directional antenna based MAC protocols by using the metric of effective spatial reuse, which is also evidenced by the simulation study.

Future Earth and space science missions are envisioned to be implemented using a flexible, distributed architecture consisting of a constellation of dynamically deployed or configured satellites that are networked together into an integrated information system. These satellites form an ad hoc network characterised by a frequently changing topology and potentially sparse and intermittent connectivity, which pose unique challenges to routing. We propose interrogation-based relay routing for ad hoc satellite networks, where the satellites interrogate each other to learn more about network topology and nodal capacity to make intelligent routing decisions. Simulations have been conducted to study the effects of satellite density and orbital patterns on throughput and delivery ratio.

This paper describes an adaptive multicast mechanism for ad hoc networks. The multicast mechanism adopts a two-tier architecture with an adaptive backbone infrastructure to integrate the effectiveness of the flooding scheme and the efficiency of the tree-based scheme for different network conditions. Coverage of a backbone node is not limited to a single hop, but is automatically adjusted according to the mobility status of each local area. Multicast capability is then provided via the construction of rendezvous-based multicast trees in the local group level and a mesh structure over the backbone level, providing both efficiency in static areas and robustness in dynamic areas. Performance evaluations are also presented.

Existing ad hoc routing protocols assume all nodes within the network to participate in the routing process. By conditionally selecting a subset of nodes is an appropriate approach to limiting the number of nodes participating in routing such that nodes not selected may be turned off to conserve power and extend network lifetime. However, not all non-routing-related nodes will be able to be turned off (suspended) at the same time. Sufficient bandwidth and forwarding capacity are still necessary in case of changing network topology and environment. We describe the coordinated power conservation (CPC) algorithm to facilitate power conservation for ad hoc networks. The algorithm constructs a backbone infrastructure to have CPC servers running on backbone nodes to coordinate suspending schedules among their local non-backbone nodes running CPC clients. Simulation results demonstrate that CPC-enabled ad hoc networks exhibit performance closely equivalent to ad hoc networks without CPC, while consuming less power.

In a match-making system, sources (producers) advertise generated data without any particular destination in mind. Destinations (consumers) are determined based on their interests (via subscriptions) in receiving the produced data. Advertisements and subscriptions are matched by the underlying network service, so that routing is based on the content of messages. We propose to facilitate a match-making capability in ad hoc and sensor networks by adapting the idea of a quorum system. A quorum system is formed by organizing nodes into subsets called quorums, where every two quorums intersect and no quorum includes another quorum. To accommodate node mobility and network scale, we propose that producers and consumers systematically forward their advertisement and subscription messages to form 'pseudo' quorums, where they are matched at intersecting nodes. Simulation results show that the pseudo quorum based matchmaking system achieves a very high matching rate with much less messaging overhead as compared to that of event and query flooding.

Topology control for ad hoc networks aims to increase effective network capacity and conserve energy. Most proposed algorithms assume the use of isotropic antennas and thus only adjust the transmission power of each node. We propose a distributed topology control mechanism for ad hoc networks with directional antennas that adjusts antenna pattern (direction) in addition to transmission power. Simulation studies have been conducted to demonstrate the effectiveness of the approach, as well as to investigate its benefits and impacts on application layer performance.

Ad hoc networks are fundamentally different from wireline networks due to the following peculiarities. Ad hoc networks are autonomously formed with a large number of heterogeneous nodes (ranging in complexity from sensors to palmtops and fully functional laptops and routers) without the aid of any pre-existing communication infrastructure. Therefore, tasks are distributed over and carried out by groups of collaborating nodes. In addition, the nodes run on battery. They will have to be power-conscious to conserve energy, and the functions offered by a node will depend on its available power level and capability. Furthermore, their topology can be highly dynamic due to autonomous mobility of nodes and physical characteristics of wireless links. Energy constraints, varying wireless communication bandwidth and quality, and node mobility result in networks becoming partitioned more frequently. These make managing ad hoc networks significantly more challenging than managing wireline networks. We propose the Guerrilla Management Architecture to satisfy the survivability, adaptability, autonomy, economy, heterogeneity, and scalability requirements in managing ad hoc networks. Success in addressing these research issues will lead to robust deployment of ad hoc networks and their effective network operations and efficient resource utilization. The Guerrilla management architecture builds on the following model and mechanisms to address these specific management requirements.

As sensor nodes are embedded into physical environments and becoming integral parts of our daily lives, sensor networks will become the important nerve systems that monitor and actuate our physical environments. We define the process of monitoring the status of a sensor network and figuring out the problematic sensor nodes sensor network diagnosis. However, the high sensor node-to-manager ratio makes it extremely difficult to pay special attention to any individual node. In addition, the response implosion problem, which occurs when a high volume of incoming replies triggered by diagnosis queries cause the central diagnosing node to become a bottleneck, is one major obstacle to be overcome. We describe approaches to addressing the response implosion problem in sensor network diagnosis. We also present simulation experiments on the performance of these approaches, and discuss presentation schemes for diagnostic results.

Data-driven label switching routers (LSR) classify flows into short-lived flows and long-lived flows. Short-lived flows are suitable for layer-3 software forwarding, while long-lived flows benefit from layer-2 hardware switching. Constrained by the capacity of an LSR, proper balance of short- and long-lived flows would maximize the overall forwarding performance, and an effective flow classification scheme is crucial. This paper proposes an approach to adaptive flow classification based on the max objective for the cache table utilization for the active long-lived flows and min objective for the average number of delayed long-lived flows, constrained by the capacity of the control processor. Based on the theoretical development, we design a controller to implement this algorithm. Simulation results show the optimality of the algorithm against the optimal solution of the static algorithm, and also demonstrate the robustness of the proposed adaptive algorithm in response to abrupt changes in the input traffic.

To sustain the ever growing demand for bandwidth in cost-effective, efficient and robust ways, it is anticipated that the next-generation transport network architecture will consist of several different technology layers. However, managing such multi-layered transport networks will be complicated and difficult, due to the scale of the networks and the correlation between different technology layers. Unfortunately, existing network management systems mainly manage a single technology, and management systems for different technologies may not interoperate. Therefore, to effectively manage the emerging multi-layered transport networks, an integrated network management system is urgently needed. In this paper, we describe work on integrated management of ATM/SONET/WDM networks from both information modeling's and software architecture's perspectives. We describe how the standard work on network-level information models may be used to model different transport technology layers and their inter-relationships. We will also describe how the CORBA technology may be used to realize the integrated information model so that the resulting integrated network management system is distributed and complies with TMN Logical Layered Architecture.

In this paper, we describes a CORBA-based framework that helps to realize the notion of the network as database. This framework shall build abstraction layers that present a distributed object database abstraction for the networks to their managers. At the bottom layer, work of the X/Open and NMF Joint Inter-Domain Management is utilized and extended to encapsulate heterogeneous network resources with CORBA objects. On top of that, standardized network-level information models define entity-relationship data models which represent logical structures of the databases containing network resources. These distributed network resources, as represented by CORBA objects, collectively constitute the distributed object database which is organized according to the data model. Facilities, such as query, trigger, and view, are then provided to facilitate network management operations. We will illustrate how the framework may be realized via CORBA Object Services, and describe its application for modeling a WDM network. With the distributed CORBA object database representation of network resources, network management activities may be carried out as conveniently as database operations, The results not only facilitate effective and consistent network management operations, but also ease the integration with Service and Business Management Layers of the TMN architecture.

To meet the demand for huge bandwidth created by the multimedia communications revolution, there is an urgent need to dramatically upgrade the existing telecommunications infrastructure. In today's infrastructure, fiber-optics is used in point-to-point transmission links, with all networking and services functions done electronically. To upgrade such an infrastructure in a cost-effective way, Wavelength Division Multiplexing (WDM) technology may be used to transmit multiple optical channels per fiber. This way, network capacity may grow in response to increased demand. In addition, with the reconfigurability of WDM networks, network configuration may adapt in response to changing traffic patterns. To ensure successful deployment and operations of WDM networks, it becomes essential to have a comprehensive network control and management system which is versatile, robust, and scaleable. In this paper, we describe a network control and management system prototype developed under the Multiwavelength Optical Networking (MONET) project funded by the US government's Defense Advanced Research Project Agency. The prototype system provides configuration, connection, fault, and performance management functionalities for reconfigurable WDM all-optical networks. The design of the prototype system follows the TMN logical layered architecture, and it is implemented on a fault-tolerant, CORBA-compliant distributed object computing platform which facilitates robust and scaleable operations.

The multiwavelength optical networking (MONET) consortium has demonstrated national-scale optical networking in a multilocation testbed in New Jersey. The demonstration involves transparent optical connections over path lengths as long as 2290 km, through several network elements (NEs) controlled by two interoperating network control and management (NC&M) systems. This paper describes in detail the three constituent testbeds and the experiments.

This paper describes the connection management research done by the Network Control and Management (NC&M) task force under the multiwavelength optical networking (MONET) program. MONET is sponsored by the Defense Advanced Research Project Agency (DARPA) the US Government Department of Defense, with participation from Bellcore, AT&T, Lucent Technologies, several government agencies, and regional Bell operating companies. MONET's vision is to develop a flexible reliable high-capacity high-performance cost-effective national optical network based on multiwavelength fiber optic technology. As an important component in realizing this vision, the MONET program includes the architecture and design of a prototype network control and management system for MONET's reconfigurable wavelength-division multiplexing (WDM) all-optical network. The primary objectives of the prototype research work are to develop the architecture and framework for managing national-scale transparent reconfigurable WDM optical networks and to demonstrate the feasibility of the NC&M prototype system in a field experiment network in Washington, DC. This prototype system allows the program participants to conduct experiments and gain experience in the management and operations of reconfigurable optical networks. This paper describes the connection management aspects of the prototype system, addressing issues such as the management architecture, information model, and provisioning algorithms of the prototype management system.

The manager/agent model has been the de facto paradigm used for designing network management systems. However, as the network size grows and new network and computing technology emerges, consistency, flexibility, reliability, and scalability issues of distributed network management systems might not be fully addressed within the model. This paper proposes an extension to the manager/agent model, called the manager/agency paradigm, to address these issues. In the manager/agency paradigm, a manager performs management functions through an agency of cooperating management entities, (lower-level) managers and/of agents, which are collaboratively working together to achieve consistent management goals. Agencies may recursively constitute other agencies, based on the layering and partitioning principles, to scale with ever growing network size. They may be organized flexibly according to different management functionalities, goals and policies, and may present a single management view to their (upper-level) managers by hiding management complexity. Inside an agency, various fault tolerant schemes, such as active replication or primary-backup approach, may be used to implement reliable management functionality transparently to its manager. The paper begins by describing the anatomy and semantics of an agency and comparing the manager/agency model against the manager/agent model. It then demonstrates its applications to address the consistency and reliability issues of network management problems. Finally, applications of the manager/agency model to the broader, distributed enterprise management is discussed.

The goal of this research is to develop a design methodology that allows performance characteristics of a system to be monitored through all stages of its development, from initial design to system deployment. The use of partially implemented performance specifications (PIPS) as the design paradigm for real-time systems is proposed. A PIPS model is a partially implemented system where some system components exist as simulation models and others as operational subsystems. The model may be executed in an appropriate operating environment to determine stochastic performance of a proposed design. Proof axioms have also been defined for the modeling primitives to allow absolute timing constraints to be verified for the model.>

An approach called MIDAS is described that supports the design of distributed systems via iterative refinement of hybrid models. A hybrid model is a partially implemented design where some components exist as simulation models and others as operational subsystems. It is an executable model and may be used to determine the stochastic performance characteristics of a partially elaborated design. MIDAS enhances the applicability of hybrid models in system design with its support for interrupts and its inclusion of distributed components in the partially implemented design. The authors describe how an existing simulation language may be extended to program hybrid models, and show how simulation algorithms may be adapted to execute hybrid models. A prototype MIDAS implementation is operational and was used to develop a set of applications. The experimental results of the exercise are also described.>

A graph matching approach is proposed in this paper for solving the task assignment problem encountered in distributed computing systems. A cost function defined in terms of a single unit, time, is proposed for evaluating the effectiveness of task assignment. This cost function represents the maximum time for a task to complete module execution and communication in all the processors. A new optimization criterion, called the minimax criterion, is also proposed, based on which both minimization of interprocessor communication and balance of processor loading can be achieved. The proposed approach allows various system constraints to be included for consideration. With the proposed cost function and the minimax criterion, optimal task assignment is defined. Graphs are then used to represent the module relationship of a given task and the processor structure of a distributed computing system. Module assignment to system processors is transformed into a type of graph matching, called weak homomorphism. The search of optimal weak homomorphism corresponding to optimal task assignment is next formulated as a state-space search problem. It is then solved by the well-known A* algorithm in artificial intelligence after proper heuristic information for speeding up the search is suggested. An illustrative example and some experimental results are also included to show the effectiveness of the heuristic search.