Identity-based key management in mobile ad hoc networks: techniques and applications [dependability in the ubiquitous wireless access]

Security is one of the major issues in MANETs. Their natural characteristics make them vulnerable to numerous severe attacks. It is widely acknowledged that cryptography provides a set of strong techniques against most vulnerabilities. Several cryptographic mechanisms for MANETs can be found in the literature. Among them, identity-based cryptographic mechanisms and key management schemes are proposed to simplify key management and to reduce the memory storage cost. This article presents the most important ID-based key management schemes, discussing their approaches, strengths, and weaknesses, and comparing their main features. It also presents the main IDbased key management application fields on MANETs. In this way it can be useful for users and researchers as a starting point on ID-based key management and its possible uses in MANETs.     

Map: a scalable monitoring system for dependable 802.11 wireless networks [dependability in the ubiquitous wireless access]

Many enterprises deploy 802.11 wireless networks for mission-critical operations; these networks must be protected for dependable access. This article introduces the MAP project, which includes a scalable 802.11 measurement system that can provide continuous monitoring of wireless traffic to quickly identify threats and attacks. We discuss the MAP system architecture, design decisions, and evaluation results from a real testbed.     

Quality of service assessment of opportunistic spectrum access: a medium access control approach [dependability in the ubiquitous wireless access]

Opportunistic spectrum access (OSA) is a promising new spectrum management approach that will allow coexistence of both licensed and opportunistic users in each spectrum band, potentially decreasing the spectrum licensing costs for both classes of users. However, this has significant implications on the QoS experienced by the licensed and opportunistic spectrum users. In this article we investigate how tolerant to secondary user activity a licensed user should be so as to provide dependable communication with sufficient QoS to an opportunistic user. We also look at key multichannel MAC features for such OSA networks proposed in the literature, and discuss how the design of control channel management affects the QoS of opportunistic users as a function of the tolerance of licensed users. We quantify the trade-off between dependability of the OSA network and the dependability of licensed users. The main conclusion is that opportunistic users can indeed achieve good QoS, as long as the licensed users are not highly active. For example, in one of the scenarios we studied, opportunistic users can achieve a delay below 100 ms if licensed user activity stays below 30 percent.     

Call admission control in wireless multimedia networks

Call admission control (CAC) is a mechanism used in networks to administer quality of service (QoS). Whereas the CAC problem in time-division multiple access (TDMA)-based cellular networks is simply related to the number of physical channels available in the network, it is strongly related to the physical layer performance in code-division multiple access (CDMA) networks since the multi-access interference in them is a function of the number of users and is a limiting factor in ensuring QoS. In this article, the CAC issues in multimedia DS-CDMA systems are reviewed by illustrating the basic principles underlying various schemes that have been proposed progressively from the simplest to the complex. The article also introduces SIR as a measure of QoS and describes the relatively simple schemes to administer CAC. The expression for SIR resulting from linear minimum mean-squared error processing is also presented. This article illustrates how CAC for multiple class service can be casted into an optimality framework and then discuss the recent work addressing self-similar multiple access interference.     

Dependability issues with ubiquitous wireless access [guest editorial]

Recent years have witnessed a proliferation of the number of wireless technologies available to access the Internet, ranging from wireless local area networks to cellular and broadcast systems, and ad hoc and mesh networks. While the emergence of these new technologies can enable truly ubiquitous Internet access, it also raises issues with the dependability of the Internet service delivered to users. Dependability in this context refers to the ability of a wireless access system to deliver specified services on which users can rely.     

Distributed call admission control in mobile/wireless networks

The major focus of this paper is distributed call admission control in mobile/wireless networks, the purpose of which is to limit the call handoff dropping probability in loss systems or the cell overload probability in lossless systems. Handoff dropping or cell overload are consequences of congestion in wireless networks. Our call admission control algorithm takes into consideration the number of calls in adjacent cells, in addition to the number of calls in the cell where a new call request is made, in order to make a call admission decision. This is done by every base station in a distributed manner without the involvement of the network call processor. The admission condition is simple enough that the admission decision can be made in real time. Furthermore, we show that our distributed call admission control scheme limits the handoff dropping or the cell overload probability to a predefined level almost independent of load conditions. This is an important requirement of future wireless/mobile networks with quality-of-service (QoS) provisioning     

QoS-aware handover control in current and future wireless/mobile networks

In this article we propose to enhance a handover management in a QoS and 4G based environments by providing a handover decision mechanism that considers QoS and other policies constraints. We introduce a policy based handover by combining the mobility management with the policy based architecture in order to achieve handovers that are triggered not only on the signal strength basis, but also on policy constraints such as cost, resource availability or load balancing. The policy based architecture will provide the handover triggering mechanism and the decision support related to the best next cell where the mobile node will move to. We also introduce mobility parameters in the Service Level Specification (sls) that specifies the handover type, the accepted handover packet loss, and the accepted handover delay. Based on thesesls mobility parameters, the QoS service classes can be mapped to the smooth handover (minimum packet loss), the fast handover (minimum delay), or the seamless handover (fast and smooth).     

无线移动网中呼叫接纳控制模型分析

新一代无线网应该能够同时支持传统的数据业务和实时交互式多媒体业务，并能够为用户提供QoS保证。在无线网中提供QoS保证，呼叫接纳控制扮演着重要的角色。对已有的呼叫接纳控制方面的研究成果进行了归纳、总结和分析，以期得出适合于无线移动多媒体网络的呼叫接纳控制模型。为适应当前的多媒体应用，侧重于对和适应性带宽分配相结合的接纳控制模型的分析。另外，介绍了与价格机制相结合的接纳控制模型，经济学概念的引入，为我们解决问题提供了一种新的视角。     

Realistic cell-oriented adaptive admission control for QoS support in wireless multimedia networks

An important quality-of-service (QoS) issue in wireless multimedia networks is how to control handoff drops. We propose admission-control algorithms that adaptively control the admission threshold in each cell in order to keep the handoff-dropping probability below a predefined level. The admission threshold is dynamically adjusted based on handoff-dropping events. We first present a simple admission-control scheme that brings out an important performance evaluation criterion - intercell fairness - and serves as a reference point. We then investigate the intercell unfairness problem and develop two enhanced schemes to overcome this problem. The performance of these protocols is benchmarked and compared with other competitive schemes. The results indicate that our schemes perform very well while, in addition, achieving significantly reduced complexity and signaling load.     

An overview of MIMO-oriented channel access in wireless networks [medium access control protocols for wireless LANs]

The integration of MIMO technology in WLANs has recently been the locus of extensive research. The main objectives of this technology are to improve channel reuse and or reduce energy consumption. In this article, we give an overview of MIMO systems and their use in WLANs. We highlight the different types of gains that MIMO offers and then discuss some of the work that has been done on MAC design. We conclude by outlining several open issues thai must be addressed for MIMO-based systems.     

Optimal rate allocation and QoS-sensitive admission control in wireless integrated networks

The problem of Call Admission Control and rate allocation in loosely coupled wireless integrated networks is investigated. The related Radio Resource Management schemes were introduced to improve network performance in wireless integrated networks. However, these schemes did not reflect the independence and competitiveness of loosely coupled wireless integrated networks. Furthermore, given that users have different requirements for price and Quality of Service (QoS), they are able to select a network according to their preference. We consider a scenario with two competitive wireless networks, namely Universal Mobile Telecommunications System cellular networks and Wireless Local Area Networks. Users generate two types of traffic with different QoS requirements: real-time and non-real-time. We propose a scheme that exploits a mathematical model for the control of call admission and adopt a noncooperative game theory-based approach to address the rate allocation problem. The purpose is to maximize the revenue of the network providers while guaranteeing a level of QoS according to user needs. Simulation results show that the proposed scheme provides better network performance with respect to packet loss rate, packet delay time, and call-blocking probability than other schemes when the data rates are allocated to each call at the point that maximizes the revenue of network providers. We further demonstrate that a Nash equilibrium always exists for the considered games.     

无线/移动网络中自适应的接纳控制算法及性能分析

无线／移动网络中重要的连接级QoS性能指标包括新连接请求阻塞率(CBP)、切换连接请求丢弃率(HDP)等。其中，更不希望因切换连接请求的丢弃而导致服务的终止。为降低HDP，通常采用资源预留方案。但这种方案导致CBP较高、资源利用率低。本文针对自适应的多媒体应用带宽可以动态调整的特点，研究无线／移动网络中多优先级服务自适应的接纳控制机制，提出一个自适应的接纳控制算法，对其QoS性能进行分析。     

URSA: ubiquitous and robust access control for mobile ad hoc networks

Restricting network access of routing and packet forwarding to well-behaving nodes and denying access from misbehaving nodes are critical for the proper functioning of a mobile ad-hoc network where cooperation among all networking nodes is usually assumed. However, the lack of a network infrastructure, the dynamics of the network topology and node membership, and the potential attacks from inside the network by malicious and/or noncooperative selfish nodes make the conventional network access control mechanisms not applicable. We present URSA, a ubiquitous and robust access control solution for mobile ad hoc networks. URSA implements ticket certification services through multiple-node consensus and fully localized instantiation. It uses tickets to identify and grant network access to well-behaving nodes. In URSA, no single node monopolizes the access decision or is completely trusted. Instead, multiple nodes jointly monitor a local node and certify/revoke its ticket. Furthermore, URSA ticket certification services are fully localized into each node's neighborhood to ensure service ubiquity and resilience. Through analysis, simulations, and experiments, we show that our design effectively enforces access control in the highly dynamic, mobile ad hoc network.     

无线移动多媒体通信网的一种切换策略

该文提出了无线移动多媒体通信网中基于宽带呼叫业务和窄带呼叫业务的双向层间切换业务模型(BLHM)和单向层间切换业务模型(SLHM),分别研究了两种业务在模型中的新呼叫阻塞概率和切换呼叫失败概率,对由于层间切换机制带来的呼叫业务质量(QoS)下降的宽带切换呼叫进行了定量分析。另外,该文还提出了基于呼叫业务代价函数和呼叫业务QoS的信道分配算法。最后进行了计算机仿真,将两种模型的性能进行了比较。     

Optimal network selection in heterogeneous wireless multimedia networks

The complementary characteristics of different wireless networks make it attractive to integrate a wide range of radio access technologies. Most of previous work on integrating heterogeneous wireless networks concentrates on network layer quality of service (QoS), such as blocking probability and utilization, as design criteria. However, from a user’s point of view, application layer QoS, such as multimedia distortion, is an important issue. In this paper, we propose an optimal distributed network selection scheme in heterogeneous wireless networks considering multimedia application layer QoS. Specifically, we formulate the integrated network as a restless bandit system. With this stochastic optimization formulation, the optimal network selection policy is indexable, meaning that the network with the lowest index should be selected. The proposed scheme can be applicable to both tight coupling and loose coupling scenarios in the integration of heterogeneous wireless networks. Simulation results are presented to illustrate the performance of the proposed scheme.     

Optimal admission control in cellular DS-CDMA systems with multimedia traffic

The problem of jointly controlling the data rates and transmit powers of users, so as to maximize throughput in cellular direct-sequence code-division multiple-access (CDMA) networks is addressed. The multicode (MC)-CDMA system, where the processing gain of each code is fixed and high-rate users use multiple codes for transmission, and the variable gain (VG)-CDMA architectures are considered. The throughout maximization problem is formulated as a classical optimization problem, modeling the constraints arising from the data rate requirements and power budgets. Optimal strategies to maximize throughput in both systems are derived. While the MC-CDMA system has a simple optimal rate-power allocation algorithm, the VG-CDMA system has a more complex solution.     

无线移动通信系统中的呼叫接入控制

呼叫接入控制是无线移动通信系统中无线资源管理的重要部分,它直接关系到系统中用户服务质量是否能够得到保证,同时呼叫接入控制算法的有效性决定了系统资源的利用效率。文中综述了各种呼叫接入控制算法及其特点,并指出在无线移动通信系统中它们的重要性。     

A dynamic call admission policy with precision QoS guarantee usingstochastic control for mobile wireless networks

Call admission control is one of the key elements in ensuring the quality of service in mobile wireless networks. The traditional trunk reservation policy and its numerous variants give preferential treatment to the handoff calls over new arrivals by reserving a number of radio channels exclusively for handoffs. Such schemes, however, cannot adapt to changes in traffic pattern due to the static nature. This paper introduces a novel stable dynamic call admission control mechanism (SDCA), which can maximize the radio channel utilization subject to a predetermined bound on the call dropping probability. The novelties of the proposed mechanism are: (1) it is adaptive to wide range of system parameters and traffic conditions due to its dynamic nature; (2) the control is stable under overloading traffic conditions, thus can effectively deal with sudden traffic surges; (3) the admission policy is stochastic, thus spreading new arrivals evenly over a control period, and resulting in more effective and accurate control; and (4) the model takes into account the effects of limited channel capacity and time dependence on the call dropping probability, and the influences from nearest and next-nearest neighboring cells, which greatly improve the control precision. In addition, we introduce local control algorithms based on strictly local estimations of the needed traffic parameters, without requiring the status information exchange among different cells, which makes it very appealing in actual implementation. Most of the computational complexities lie in off-line precalculations, except for the nonlinear equation of the acceptance ratio, in which a coarse-grain numerical integration is shown to be sufficient for stochastic control. Extensive simulation results show that our scheme steadily satisfies the hard constraint on call dropping probability while maintaining a high channel throughput