Wireless sensor networks (WSNs) are one of the most important ingredients in the Internet of Things. Thus it is vital to design a good power saving protocol, which operates at the medium access control (MAC) layer, for a WSN since sensors are generally battery-powered. On the other hand, organizing a WSN into coronas centered at the sink is a simple effective technique to achieve low-overhead routing where every sensor needs neither to broadcast beacons nor to maintain routing/neighbor tables. Hence in this paper, we propose an optimal and maximized configurable power saving protocol, named Green-MAC, for a corona-based WSN, which has the following attractive features. (i) By using the generalized Chinese remainder theorem, Green-MAC guarantees that any two sensors in the neighboring coronas can simultaneously wake up in bounded time regardless of their schedule offset as well as their respective cycle lengths. (ii) Given the cycle length, the ATF-ratio (i.e. the fraction of awake time frames in a cycle) of each sensor reaches the theoretical minimum. (iii) Under the minimum ATF-ratio constraints, the number of configurable ATF-ratios of each sensor reaches the theoretical maximum. (iv) An ATF-ratio configuration scheme is proposed for Green-MAC such that the power consumption of a WSN can be minimized while the worst event-to-sink delay requirement can be fulfilled with high probability. Both theoretical analysis and simulation results demonstrate that Green-MAC greatly outperforms existing power saving protocols for corona-based WSNs, including Q-MAC and Queen-MAC, in terms of ATF-ratio, configurability, network lifetime, delay violation ratio, and event-to-sink throughput.

In recent years, with the economic development and urbanization, traffic congestion has become a serious problem in urban environments. Traffic signal control plays a key role in Intelligent Transportation System (ITS). Particularly, bus system can carry a higher capacity of passengers, which help to relief traffic jam in cities. However, different from ordinary vehicles, bus system has several unique features, including higher capacity of passengers, fixed routes and specific requirements on arrival time and headway. In this paper, we propose an adaptive traffic signal control approach with bus Priority that determines the phase sequence and time in non-fixed order based on synergic information to improve the performance of bus system with a very small cost to ordinary vehicles. Simulation results show that our approach can significantly reduce the waiting time of buses, keep bus schedules on time, and regular bus headway.

We consider the channel assignment problem in wireless mesh networks. Due to the limited number of radio interfaces that each node is equipped with, channel assignment must ensure that the interface constraint is obeyed, i.e., the number of different channels assigned to the links incident on a node must be no greater than the number of interfaces the node is equipped with. However, interface constraint may be one of the causes that hinder the performance of some of the existing heuristics. In this paper, we use simulated annealing to solve the channel assignment problem in wireless mesh networks. We propose two neighbor generating approaches that handle the interface constraint in different ways. The first approach starts with an infeasible random solution, and by using the penalty function technique the solution finally converges to a feasible one. The second approach, on the contrary, allows only feasible solutions to be generated during the simulated annealing process. Simulations are conducted that compare our proposed simulated annealing algorithms together with a tabu-based algorithm under different network traffic scenarios. The results show that our algorithms exhibit lower network interference than the tabu-based algorithm.

Existing data dissemination protocols adopted flooding to propagate interests and find forwarding paths in wireless sensor networks (WSNs), which cause large energy consumption. To relieve this problem, we propose an efficient cluster-based data dissemination (ECDD) scheme. In the proposed ECDD, besides piggyback control information into interests to perform on-demand passive clustering, we also use control information to set each node a hop count for assisting a node to select next forwarding node with the least hop count to the sink. In this way, a shortest path to forward sensed data back to the sink can be found. Simulation results show that the proposed ECDD is 61.30% better than DD, a classical approach, and 22.33% better than ELPC in terms of average dissipated energy. Furthermore, our approach is 57.45% and 23.49% better than DD and ELPC, respectively, in terms of average delay. The proposed ECDD is feasible for applications of long-term monitoring and real-time response, such as a community health care system and rescue operation in a disaster area.

Abstract User authentication is a critical part of security, along with confidentiality and integrity, for computer systems that allow legitimate users remote access over an open communication network. Recently, user authentication for wireless sensor networks (WSNs) has received considerable attention. We propose a robust user authentication scheme for WSNs. The scheme is based on elliptic‐curve cryptosystems with self‐certificates. The proposed scheme allows users to change their key pairs without interaction with a key distribution center (KDC). Moreover, the proposed scheme still works well even if the adversary captures tnodes out of nnodes in the WSNs. Security of the proposed scheme is modeled and analyzed with Petri nets. Our analysis shows that the proposed scheme can successfully defend some of the most notorious attacks, including replay attacks, forgery attacks, and node‐capture attacks. Copyright © 2010 John Wiley & Sons, Ltd.

IEEE 802.11 is currently the most popular medium access control (MAC) standard for mobile ad hoc networks (MANETs). On the other hand, clustering in MANETs is a promising technique to ensure the scalability of various communication protocols. Thus, we propose an optimal asymmetric and maximized adaptive power management protocol, called OAMA, for 802.11-based clustered MANETs, which has the following attractive features. 1) Given the length of schedule repetition interval (SRI), the duty cycles of both clusterheads and members reach the theoretical minimum. 2) Under the minimum duty cycle constraints, the numbers of tunable SRIs for clusterheads and members reach the theoretical maximum. 3) By means of factor-correlative coterie-plane product, OAMA guarantees bounded-time neighbor discovery between the clusterhead and its member, and between all clusterheads, regardless of stations' individual SRIs and the schedule offset between neighboring stations. 4) The time complexity of OAMA neighbor maintenance is O(1). 5) OAMA adopts a cross-layer SRI adjustment scheme such that stations can adaptively tune the values of SRI to maximize energy conservation according to flow timeliness requirements. Both theoretical analyses and simulation results show that OAMA substantially outperforms existing power management protocols for clustered MANETs, including AQEC [2] and ACQ [14], in terms of duty cycle, adaptiveness, data delay dropped ratio, network lifetime, and end-to-end energy throughput.

In MANETs, mobile devices are usually powered by batteries with limited energy supplies. Topology control is a promising approach, which conserves energy by either reducing transmission power for each node or preserving energy-efficient routes for the entire network. However, there is empirically a trade-off between the energy efficiency of the nodes and routes in a topology. Besides, it may consume considerable energy to maintain the topology due to node mobility. In this paper, we propose an adaptive topology control protocol for mobile nodes. The protocol allows each node to decide whether to support energy-efficient routing or conserve its own energy. Moreover, it can drastically shrink the broadcasting power of beacon messages for mobile nodes. We prove that any reconstruction and change of broadcasting radius converge in four and five beacon intervals, respectively. The experimental results show that our protocol can significantly reduce the total energy consumption for each successfully transmitted packet, and prolong the life times of nodes, especially in high mobility environments.

With the extension of wireless technology, vehicular ad hoc networks (VANETs) provide general data transmission services and emergency warning services. To rescue more drivers from being involved in an emergency event on the road, fast emergency message propagation is an important issue in VANET studies. There are two types of multi-hop broadcasting forwarder selection schemes for emergency broadcasting, known as sender-oriented schemes and receiver-oriented schemes. The sender-oriented schemes periodically maintain neighbor information in order to choose the best forwarder before broadcasting the message, while the receiver-oriented schemes distributed elect the forwarders. In this paper, we propose a vehicle-density-based emergency broadcast (VDEB) scheme to solve the problem of high overhead in sender-oriented schemes, and long delay in receiver-oriented schemes. The simulation results show that our VDEB scheme can achieve better performance with low delay and little overhead.

A key agreement protocol is a protocol whereby two or more communicating parties can agree on a key or exchange information over an open communication network in such a way that both of them agree on the established session keys for use in subsequent communications. Recently, several key agreement protocols based on chaotic maps are proposed. These protocols require a verification table to verify the legitimacy of a user. Since this approach clearly incurs the risk of tampering and the cost of managing the table and suffers from the stolen-verifier attack, we propose a novel key agreement protocol based on chaotic maps to enhance the security. The proposed protocol not only achieves mutual authentication without verification tables, but also allows users to anonymously interact with the server. Moreover, security of the proposed protocol is modelled and analyzed with Petri nets. Our analysis shows that the proposed protocol can successfully defend replay attacks, forgery attacks, and stolen-verifier attacks.

This paper studies the problem of multicast routing and channel assignment in multi-channel and multi-interface wireless mesh networks. The advantage of the wireless broadcast's nature is used to reduce interference and improve network throughput. The employed network model is first described. Next, a heuristic channel assignment algorithm that makes use of the wireless broadcast's advantage is presented. Simulation results reveal that the proposed heuristic algorithm can reduce interference and increase the network throughput in multi-channel multi-interface wireless mesh networks.

In this paper, we designed and implemented a dependable SIP-based clustered architecture for VoIP and multimedia applications, and also proposed an efficient OpenAIS-based SIP load balancing strategy (OSLB) that can balance proxy serverspsila load and achieve fast failover by reducing the number of failed calls when one of the dispatchers or one of the SIP proxy servers crashes. Experimental results show that our OSLB is comparable to an existing work, SIP load balancer, in terms of load balance metric (1.05 vs. 1.04). However, our OSLB reduces the number of failed calls by 86% when a proxy server failed compared to the SIP load balancer. This work, which is part of an EPON project, has been realized in an industry standard ATCA-based platform to provide high availability carrier-grade services, and is currently under a field trial in an ISP.

Since multi-hop mobile ad hoc network (MANET) contains a set of wireless mobile nodes forming a temporary network, the topology is strongly influenced by the node mobility models. Numerous mobility models have been presented, including the Random Waypoint Mobility Model (RWMM), Manhattan Grid Mobility Model (MGMM), Freeway Mobility Model (FMM), and so on. In MGMM, the trajectories of mobile nodes are confined to a grid topology. MGMM is an important mobility model, and numerous objects following MGMM can be enumerated, such as the movement of cars in the city, the movement of people though department stores etc. The expected link life time (ELLT) is an important performance parameter in MANET. When a node wishes to transmit information to the other node directly, these two nodes must be within each other's transmission range for a period of time. This period is called the link life time (LLT). The ELLT is the expected value of LLT. The goal of this work largely focuses on identifying the ELLT of the MANET under MGMM by using mathematical analysis. Based on our observation, two nodes involved in constructing a connection under MGMM can be classified into three independent cases: namely parallel with opposite directions, parallel with same directions, and vertical cases. These three cases can be formulated independently. To verify these formulations numerous simulations are done by ns2, and the theoretical and simulation results are well matched.

This paper proposes an energy-efficient traffic scheduling approach for 802.16e broadband wireless networks. Instead of considering a single Mobile Subscriber Station (MSS) as most of the current researchers do, multiple MSSs are considered in our work. The constant bit rate traffic with QoS delay constraint is considered in this paper. The proposed approach considers both energy efficiency and bandwidth utilization. First, we derive a minimum wakeup time for each MSS to achieve the maximum power saving by waking up the minimum number of time slots. After then, we interleave the traffic of multiple MSSs by taking advantage of feasible slot allocation. In order to support the maximum number of MSSs, our scheduling problem can be transformed into a maximum bipartite matching problem. We use the Ford-Fulkerson maximum flow algorithm to obtain a feasible schedule for multiple MSSs. Simulation results show that our proposed approach has better bandwidth utilization and achieves maximum energy saving.

Abstract Smart card‐based authentication is one of the most widely used and practical solutions to remote user authentication. Compared to other authentication schemes, our proposed scheme aims to provide more functionalities and to resist well‐known attacks. These crucial merits include (1) a user can freely choose and change his passwords; (2) our scheme provides mutual authentication between a server and a user; (3) it achieves user anonymity; (4) a server and a user can generate authenticated sessions keys. Moreover, our scheme can resist replay attacks, forgery attacks, insider attacks, reflection attacks, and parallel session attacks. Copyright © 2008 John Wiley & Sons, Ltd.

Over the last few years, many researchers have paid a lot of attention to the user authentication problem. However, to date, there has been relatively little research suited for wireless sensor networks. Recently, Wong et al. proposed a dynamic user authentication scheme for WSNs that allows legitimate users to query sensor data at every sensor node of the network. We show that Wong et al.'s scheme is vulnerable to the replay and forgery attacks and propose a lightweight dynamic user authentication scheme for WSNs. The proposed scheme not only retains all the advantages in Wong et al.'s scheme but also enhances its security by withstanding the security weaknesses and allows legitimate users to change their passwords freely. In comparison with the previous scheme, our proposed scheme possesses many advantages, including resistance of the replay and forgery attacks, reduction of user's password leakage risk, capability of changeable password, and better efficiency.

This paper proposes three energy efficient scheduling approaches for 802.16e broadband wireless networks. Instead of considering a single Mobile Subscriber Station (MSS) as most of the current researchers do, multiple MSSs are considered in our work. The constant bit rate traffic with QoS delay constraint is considered in this paper. The proposed approaches address both energy efficiency and bandwidth utilization. We reuse the idle fragmentation of the allocated OFDM frames to balance power saving and bandwidth utilization. Simulation results show that our proposed approaches benefit with more sleep time and higher bandwidth utilization. Furthermore, we give a QoS scheduling mechanism to find the maximum sleeping time for single MSS, called Minimum Wakeup Time (MWT) scheduler. Even though we don't know whether exists a feasible scheduling to satisfy all MSSs with MWT, it will serve as an upper bound for the power-saving scheduling in IEEE 802.16e.

This paper proposes a highly-available open shortest path first (HA-OSPF) router which consists of two OSPF router modules-active and standby-to support a high-availability network. Each router module runs a Linux operating system, high-availability management middleware (HAM middleware), and OSPF daemon. The HAM middleware consists of an availability management framework (AMF) service, checkpoint service, interface monitor, OSPF fault manager, and fault handler; it provides a health check, state information exchange, and takeover mechanism. The experimental results are given to show the system availability of the HA-OSPF router on a PC-based prototype system. Furthermore, to build a carrier grade commercial product, we realize a HA-OSPF router on an industry standard compliant advanced telecom computing architecture (ATCA) hardware platform. From actual measurements, we show that our PC-based and ATCA-based HA-OSPF routers take only 166 and 131 ms to switch over to a standby router module when there is a software fault and 360 and 331 ms with a hardware failure respectively.

The SIP proxy server, which is an important building block of a SIP network, can be in a form of a cluster to prevent service unavailability caused by software or hardware failures. The design of a SIP proxy server cluster with a single dispatcher in a SIP network faces the single-point-offailure problem. The use of dual SIP dispatcher architecture was proposed and VRRP (Virtual Router Redundancy Protocol) was used as an IP failover mechanism. In this paper, we have designed and implemented a dependable SIP network that includes n + k SIP dispatchers (n active dispatchers + k backup dispatchers) to control and monitor a cluster ofm SIP proxy servers for VoIP and video conferencing applications. A fast failure detection and failover (FFF) scheme has also been proposed. FFF uses OpenAIS as a high availability middleware to perform health check and failover of dispatchers and proxy servers. Experimental results have shown that the FFF scheme reduces the dispatcher failover time by 80 % compared to the VRRP mechanism and also shorten the proxy failover time by 85 % compared to the mechanism provided by OpenSER itself.

In mobile ad hoc networks, nodes are usually powered by batteries with limited energy. To prolong the network life, the energy consumption of the routing task is crucial. In previous works, enormous topology control methods were given to support the energy-efficient routing, while the most of them are designed for static network. In this paper, we proposed a novel topology control scheme for mobile nodes. It is based on an adjustable structure, named the r-neighborhood graph. Simulation results show the proposed scheme can significantly improve the energy consumption especially in high mobility environment.

In wireless ad hoc networks, constructing and maintaining a topology with lower node degrees is usually intended to mitigate excessive traffic load on wireless nodes. However, keeping lower node degrees often prevents nodes from choosing better routes that consume less energy. Therefore, the trade-off is between the node degree and the energy efficiency. In this paper, an adjustable structure, named the r-neighborhood graph, is proposed to control the topology. This structure has the flexibility to be adjusted between the two objectives through a parameter r, 0lesrles1. More explicitly, for any set of n nodes, the maximum node degree and power stretch factor can be bounded from above by some decreasing and increasing functions of r, respectively. Specifically, the bounds can be constants in some ranges of r. Even more, the r-neighborhood graph is a general structure of both RNG and GG, two well-known structures in topology control. Compared with YGk, another famous adjustable structure, our method always results in a connected planar with symmetric edges. To construct this structure, we investigate a localized algorithm, named PLA, which consumes less transmitting power during construction and executes efficiently in O(n logn) time

The emergence of multi-channel multi-radio wireless mesh networks has given us many new opportunities and challenges. Particularly, the issue on how to appropriately assign channels to interfaces has gathered great importance in the recent publications. To efficiently utilize the channels diversity, the communicating channels should be negotiated between interfaces, which would cause considerable overhead. To conquer this, a hybrid scheme was proposed to rule the way for assigning channels in literatures. In this paper, we formally model the hybrid scheme into an integer linear programming formulation. We provide the necessary as well as sufficient conditions of any feasible assignment. To optimize the link-layer performance, we suggest an objective function which minimizes the total potential interference. We also show that the approximability of the considered problem.

Abstract One of the most important applications for mobile commerce is location‐based application and the core technology of location‐based applications is the location‐determination technology. In this paper, we present a location‐sensing method, calledcell‐based location‐sensing methodand its positioning accuracy for the wireless networks with hexagonal structure and mesh structure. In addition, the accuracy of the method is optimized by tuning the transmitting power of base stations. In the optimal transmitting power, an accuracy of within 9.1667% (7.2182%) cell area for hexagonal structure (mesh structure) can be achieved by the cell‐based location‐sensing method. We believe that the results are useful for deploying wireless networks for location‐based applications. Copyright © 2003 John Wiley & Sons, Ltd.

One of the most important applications for mobile commerce is location-based application and the core technology of location-based applications is the location determination technology. In this paper, we present a positioning method, called cell-based positioning method and its positioning accuracy measure for the wireless networks with hexagon structure and mesh structure. In addition, the positioning accuracy is optimized by tuning the base stations' transmission power. In the optimal transmission power an accuracy of within 9.1% (7.2%) cell area for hexagonal structure (mesh structure) can be achieved by cell-based positioning method. We believe that the results are useful to deploy wireless networks for location-based applications.

A computation task running in distributed systems can be represented as a directed graph H(V, E) whose vertices and edges may fail with known probabilities. In this paper, we introduce a reliability measure, called the distributed task reliability, to model the reliability of such computation tasks. The distributed task reliability is defined as the probability that the task can be successfully executed. Due to the and-fork/and-join constraint, the traditional network reliability problem is a special case of the distributed task reliability problem, where the former is known to be NP-hard in general graphs. For two-terminal and–or series-parallel (AOSP) graphs, the distributed task reliability can be computed in polynomial time. We consider a graph Hk(Vˆ, Eˆ), named a k-replicated and–or series-parallel (RAOSP) graph, which is obtained from an AOSP graph H(V, E) by adding (k - 1) replications to each vertex and adding proper edges between two vertices. It can be shown that the RAOSP graphs are not AOSP graphs; thus, the existing polynomial algorithm does not apply. Previously, only exponential time algorithms as used in general graphs are known for computing the reliability of Hk(Vˆ, Eˆ). In this paper, we present a linear time algorithm with O(K(|V| + |E|)) complexity to evaluate the reliability of the graph Hk(Vˆ, Eˆ), where K = max{k222k, 23k}. © 1997 John Wiley & Sons, Inc.

This paper proposes a simple assembly/disassembly part (ADP) for the Signalling System No.7 (SS7) protocol to reduce the signalling traffic load in intelligent networks (IN) and personal communication service (PCS) networks. The ADP combines two or more messages with the same destinations into a single message and then the signalling traffic is reduced. In addition, the ADP will not affect the SS7 protocol operations. The numerical results show the proposed method can reduce traffic 9%/spl sim/17% among signalling points.

The objective is to find the topological layout of links at a minimal cost under the constraint that the overall reliability of the constructed network is not less than a given level of system reliability. A decomposition method which is based on a branch-and-bound approach is proposed for solving it. A method is presented to determine a lower bound on the minimum number of links in a network which may satisfy the reliability constraint. The solution method is illustrated with a numerical example, and computational experiments are also given.>