Neighbor discovery and stateless autoconfiguration in IPv6

The next-generation Internet Protocol, IPv6, includes autoconfiguration facilities that allow IPv6 hosts to plug into the network and start communicating with no special configuration required. These facilities address the requirements of hosts connecting to isolated standalone networks (such as home networks). The paper considers how the neighbor discovery protocols provide address-resolution services and allow hosts to find and keep track of routers, determine when a neighbor becomes unreachable, and switch dynamically to backup routers should the ones they are using fail     

On the nominal capacity of multi-radio multi-channel wireless mesh networks

Wireless mesh networking is an emerging technology with a wide range of applications, from community to metropolitan area networking. Mesh networks consist of wireless routers and access points that make up the network backbone which is connected to the wired infrastructure. Client devices are located at the edge. The capacity of a wireless mesh network is an important performance indicator as well as design parameter. It depends on various factors such as network size and topology, expected traffic patterns, number of interfaces per node, number of channels, routing and channel assignment etc. In this paper, we present an analytical framework for estimating the capacity of wireless mesh networks, based on the concept of collision domains. The capacity of grid-oriented mesh networks is investigated for various scenarios to study the impact of different network parameters.     

Design and implementation of MobiSEC: A complete security architecture for wireless mesh networks

Wireless mesh networks (WMNs) have emerged recently as a technology for next-generation wireless networking. They consist of mesh routers and clients, where mesh routers are almost static and form the backbone of WMNs. WMNs provide network access for both mesh and conventional clients.In this paper we propose MobiSEC, a complete security architecture that provides both access control for mesh users and routers as well as a key distribution scheme that supports layer-2 encryption to ensure security and data confidentiality of all communications that occur in the WMN.MobiSEC extends the IEEE 802.11i standard exploiting the routing capabilities of mesh routers; after connecting to the access network as generic wireless clients, new mesh routers authenticate to a central server and obtain a temporary key that is used both to prove their credentials to neighbor nodes and to encrypt all the traffic transmitted on the wireless backbone links.A key feature in the design of MobiSEC is its independence from the underlying wireless technology used by network nodes to form the backbone. Furthermore, MobiSEC allows seamless mobility of both mesh clients and routers.MobiSEC has been implemented and integrated in MobiMESH, a WMN implementation that provides a complete framework for testing and analyzing the behavior of a mesh network in real-life environments. Moreover, extensive simulations have been performed in large-scale network scenarios using Network Simulator.Numerical results show that our proposed architecture considerably increases the WMN security, with a negligible impact on the network performance, thus representing an effective solution for wireless mesh networking.     

A hierarchical architecture for detecting selfish behaviour in community wireless mesh networks

Wireless mesh networks (WMNs) consist of dedicated nodes called mesh routers which relay the traffic generated by mesh clients over multi-hop paths. In a community WMN, all mesh routers may not be managed by an Internet Service Provider (ISP). Limited capacity of wireless channels and lack of a single trusted authority in such networks can motivate mesh routers to behave selfishly by dropping relay traffic in order to provide a higher throughput to their own users. Existing solutions for stimulating cooperation in multi-hop networks use promiscuous monitoring or exchange probe packets to detect selfish nodes and apply virtual currency mechanism to compensate the cooperating nodes. These schemes fail to operate well when applied to WMNs which have a multi-radio environment with a relatively static topology. In this paper we, propose architecture for a community WMN which can detect selfish behaviour in the network and enforce cooperation among mesh routers. The architecture adopts a decentralized detection scheme by dividing the mesh routers into manageable clusters. Monitoring agents hosted on managed mesh routers monitor the behaviour of mesh routers in their cluster by collecting periodic reports and sending them to the sink agents hosted at the mesh gateways. To make the detection more accurate we consider the quality of wireless links. We present experimental results that evaluate the performance of our scheme.     

An experimental evaluation of cross-layer routing in a wireless mesh backbone

Over the latest few years, cross-layer design in wireless networks has drawn great attention from the research community. One of the main arguments in favor of such techniques is that the hop-count metric alone is not enough to capture the specificities of wireless links (e.g., interferences, collisions, fading). In this paper, we address a simple yet fundamental question: What are the real improvements that cross-layering can bring to routing performance when compared to the simple hop-count metric? In our experiments, we consider the backbone of a real wireless mesh network composed of 12 routers deployed in an office building. We focus on the stability of routes and their persistence. In spite of the nature of cross-layer metrics that take into account information from different layers, lets them be very reactive to changes, we observe that using these metrics, pairs of nodes tend to mainly use the same set of two or three routes between them.     

Design and evaluation of a fast MAC layer handoff management scheme for WiFi-based multichannel Vehicular Mesh Networks

Vehicular Mesh Networks (VMNs) are important components of the wireless metropolitan networks. Compared with traditional wireless networks, they are more efficient in terms of deployment, configuration, and maintenance. However, connecting all mesh routers through wireless connection in VMNs results in the network backbone's remarkably lower bandwidth. Multichannel technology, where non-interfering channels are used to enable mesh routers to send and receive packets simultaneously, can be adopted to improve the throughput of VMNs. Due to the limited radio range of mesh routers, mobile clients have to switch among different mesh routers to maintain wireless connections. Therefore, providing smooth roaming in multichannel VMNs has become an important topic in VMN research. In this paper, a novel MAC layer handoff scheme is proposed as a means of minimizing handoff latency for WiFi-based multichannel VMNs to provide smooth communication for real-time applications. By designing a dynamic grouping algorithm for channel selection and allowing mesh routers to switch their channels for probe response messages, our scheme can shorten the waiting time for the detection of available access routers, decrease the loss ratio of data packets during the handoff, and consequently achieve smooth handoff in the MAC layer.     

Routing Internet traffic in heterogeneous mesh networks: Analysis and algorithms

In practical wireless mesh networks (WMNs), gateways are subject to hard capacity limits on the aggregate number of flows (in terms of bit rate) that they can support. Thus, if traffic is routed in the mesh network without considering those constraints, as well as the traffic distribution, some gateways or intermediate mesh routers may rapidly get overloaded, and the network resources can be unevenly utilized. To address this problem, in this paper we firstly develop a multi-class queuing network model to analyze feasible throughput allocations, as well as average end-to-end delay, in heterogeneous WMNs. Guided by our analysis, we design a Capacity-Aware Route Selection algorithm (CARS), which allocates network paths to downstream and upstream Internet flows so as to ensure a more balanced utilization of wireless network resources and gateways’ fixed connections. Through simulations in a number of different network scenarios we show that the CARS scheme significantly outperforms conventional shortest path routing, as well as an alternative routing method that distributes the traffic load on the gateway nodes to minimize its variance.     

SAAMAN: Scalable Address Autoconfiguration in Mobile Ad Hoc Networks

Address autoconfiguration is one of the fundamental issues in mobile ad hoc networks (MANET). A node must need some form of identity before participating in any sort of communication. So each host in a MANET needs to be uniquely addressed so that the packets can be relayed hop-by-hop and delivered ultimately to the desired destination. Moreover, nodes in the MANET are free to move and organize themselves in an arbitrary fashion. Therefore any fixed infrastructure based solution for assigning identity (i.e. IP address) is not directly applicable to MANET. Under this infrastructureless and sporadic nature of the mobile nodes, several protocols of address autoconfiguration in the mobile ad hoc networks (MANET) have been proposed. Although some of these protocols perform decently in sparse and small networks, but exhibit poor performance (e.g., single point of failure, storage limitation, large protocol overhead and so on) when the network is either dense or very large. In this paper, we propose an efficient and scalable address autoconfiguration protocol that automatically configures a network by assigning unique IP addresses to all nodes with a very low overhead and minimal cost. Evenly distributed Duplicate-IP address Detection Servers are used to ensure the uniqueness of an IP address during IP address assignment session. In contrast to some other solutions, the proposed protocol does not exhibit any problems pertaining to leader election or centralized server-based solutions. Furthermore, grid based hierarchy is used for efficient geographic forwarding as well as for selecting Duplicate-IP address Detection Servers. Through simulation results we demonstrate scalability, robustness, low latency, fault tolerance and some other important aspects of our protocol.     

Survivable and delay-guaranteed backbone wireless mesh network design

Backbone wireless mesh networks (BWMNs) consisting of wireless mesh routers are emerging alternatives to implementations of metropolitan area networks (MANs). In a BWMN, gateways connect to the Internet via wireline links and provide Internet access services for users. Due to the limited wireless channel bit rate, multiple gateways are usually required in a BWMN, which costs budget and takes time to set up. In this paper, we study the network topology design and the gateway arrangement so that the construction cost of a BWMN is minimal. Two algorithms, namely, the Predefined Gateway Set Algorithm (PGSA) and the Self-Constituted Gateway Algorithm (SCGA), are proposed for the BWMN design. A genetic algorithm and a proposed enhanced Djikstra's algorithm are employed to search for the low-cost network configuration with constraints such as survivability, link capacity, degree limitation and maximum tolerable delay. Computational results show that the PGSA can give an acceptable network configuration rapidly. In case the gateway cost is high, using the SCGA can lower the network construction cost at the expense of more computational time.     

Dynamic address autoconfiguration in hybrid ad hoc networks

The use of ad hoc networking technologies is emerging as a viable and cost-effective solution to extend the range of traditional wireless local area networks (WLANs). In these networks, mobile client traffic reaches the access points through multi-hop wireless paths that are established by using an ad hoc routing protocol. However, several technical challenges have to be faced in order to construct such an extended WLAN. For instance, traditional autoconfiguration protocols commonly used in infrastructure-based WLANs, such as DHCP or Zeroconf, are not directly applicable in multi-hop wireless networks. To address this problem, in this paper we propose extensions to DHCP to enable the dynamic allocation of globally routable IPv4 addresses to mobile stations in hybrid ad hoc networks, which transparently integrate conventional wired technologies with wireless ad hoc networking technologies. Some of the attractive features of our solution are its ability to cope with node mobility, the introduction of negligible protocol overheads, and the use of legacy DHCP servers. We have implemented a prototype of our scheme, and tested its functionalities considering various topology layouts, network loads and mobility conditions. The experimental results show that our solution ensures short address configuration delays and low protocol overheads.     

Zero-Degree algorithm for Internet GateWay placement in backbone wireless mesh networks

Internet GateWays (IGWs) are responsible for connecting the backbone wireless mesh networks (BWMNs) to the Internet/wired backbone. An IGW has more capabilities than a simple wireless mesh router (WMR) but is more expensive. Strategically placing the IGWs in a BWMN is critical to the Wireless Mesh Network (WMN) architecture. In order to solve the problem of IGWs placement in BWMNs, a novel algorithm is proposed in this paper. The new algorithm is involved in placing a minimum number of IGWs so that the Quality of Service (QoS) requirements are satisfied. Different from existing algorithms, this new algorithm incrementally identifies IGWs and prioritively assigns wireless mesh routers (WMRs) based on the computed degree of WMRs to identified IGWs. Performance evaluation results show that proposed algorithm outperforms other alternative algorithms by comparing the number of gateways placed in different scenarios. Furthermore, having control of the distribution of IGWs in order to locate them closest to available Internet/wired network connection points is an added advantage of this algorithm.     

Portable wireless-networking protocol evaluation

Multi-hop wireless networks, such as sensor-, ad hoc- and mesh-nets, can be differentiated in terms of participating devices and usage scenarios. However they share strong characteristics and requirements, such as node cooperation to enable multi-hop forwarding and dynamic routing protocols to deliver packets. As a result of these similarities, protocols designed for all these wireless networks revolve around a common core of functionality, for example coping with link and node dynamics. They differ only in additional network-specific functionality, such as tree routing structures in sensornets, and parameterization, for example buffer sizes.This convergence of functionality and design goals, as well as the sheer number of proposed protocols in each network class, motivates the idea of applying protocols to more than just their one original class. However, network-layer protocols are usually developed for and tested in only one class of wireless network due to the lack of a platform that allows testing of protocols across different classes of networks. As a result, we unnecessarily constrain the range of settings and scenarios in which we test network protocols.In this article, we propose a platform for protocol testing and evaluation in multiple, heterogeneous networks and discuss the requirements and challenges of such a solution. As a first step and case study, we present the detailed architecture of TinyWifi, a platform for executing native sensornet protocols on Linux-driven wireless devices as found in wireless mesh and mobile ad-hoc networks (MANETs). TinyWifi builds on nesC code base that abstracts from TinyOS and enables the execution of nesC-based protocols in Linux. Using this abstraction, we expand the applicability and means of protocol execution from one class of wireless network to another without re-implementation. We demonstrate the generality of TinyWifi by evaluating four well-established protocols on IEEE 802.11 and 802.15.4 based testbeds using a single implementation. Based on the experience of building TinyWifi and the presented evaluation, we deduce the feasibility of a cross-network evaluation platform and sketch the requirements for inclusion of further network classes.     

一种基于历史信任数据的DDOS防御模型

分布式拒绝服务攻击给网络安全和网络服务质量带来了巨大的威胁。通过对分布式拒绝服务攻击原理及现有防御措施的分析,为了更有效防御这类攻击的发生,可以考虑在边界路由器上建立一种基于历史信任数据的源地址库的防御模型。该模型以历史信任数据库为依托,通过对异常IP包使用核心无状态公平排队算法进行源地址检测并对其处理结果做出相应的处理,可以有效、快速过滤掉异常的IP包数据,提前防止网络受到分布式拒绝服务攻击的侵害。     

Application-aware scheduling for VoIP in Wireless Mesh Networks

Wireless Mesh Networks (WMNs) are seen as a means to provide last mile connections in Next Generation Networks (NGNs). Because of their auto-configuration capabilities and the low deployment cost WMNs are considered to be an efficient solution for the support of multiple voice, video and data services in NGNs. This paper looks at the optimal provision of resources in WMNs for Voice over IP (VoIP) traffic, which has strict performance requirements in terms of delay, jitter and packet loss. In WMNs, because of the challenges introduced by wireless multi-hop transmissions and limited resources, providing performance quality for VoIP comparable to the voice quality in the traditional circuit-switched networks is a major challenge.This paper analyses different scheduling mechanisms for TDMA-based access control in mesh networks as specified in the IEEE 802.16-2004 WiMAX standard. The performance of the VoIP applications when different scheduling mechanisms are deployed is analysed on a variety of topologies using ns-2 simulation and mathematical analysis. The paper concludes that on-demand scheduling of VoIP traffic – typically deployed in 802.11-based WMNs – is not able to provide the required VoIP quality in realistic mesh WiMAX network scenarios and is therefore not optimal from a network operator’s point of view. Instead, it is shown, that continuous scheduling is much better suited to serve VoIP traffic. The paper then proposes a new VoIP-aware resource coordination scheme and shows, through simulation, that the new scheme is scalable and provides good quality for VoIP service in a wide range of network scenarios. The results shown in the paper prove that the new scheme is resilient to increasing hop count, increasing number of simultaneous VoIP sessions and the background traffic load in the network. Compared to other resource coordination schemes the VoIP-aware scheduler significantly increases the number of supported calls.     

A quality based routing protocol for wireless mesh networks

Wireless mesh networks can provide low-cost solutions for extending the reach of wireless access points by using multi-hop routing over a set of stationary wireless routers. The routing protocol for these networks may need to address quality considerations to meet the requirements of the user. In this paper, we present a quality based routing protocol for wireless mesh networks that tries to maximize the probability of successful transmissions while minimizing the end-to-end delay. The proposed routing protocol uses reactive route discoveries to collect key parameters from candidate routes to estimate the probability of success and delay of data packets transmitted over them. To achieve accurate route quality assessments, a new route quality metric is proposed that uses performance models of data packet transmissions as opposed to estimating route quality from the transmission of control packets, which have different transmission characteristics. These models are developed after careful evaluations of multi-hop wireless transmissions and validated by computer simulations. Relevant parameters that can be used to assess the route quality metric using these models are explained. Extensive performance evaluations of the proposed quality based routing protocol are presented and its benefits in comparison to some other known routing protocols are discussed.     

一种基于历史信任数据的DDOS防御模型

分布式拒绝服务攻击给网络安全和网络服务质量带来了巨大的威胁。通过对分布式拒绝服务攻击原理及现有防御措施的分析，为了更有效防御这类攻击的发生，可以考虑在边界路由器上建立一种基于历史信任数据的源地址库的防御模型。该模型以历史信任数据库为依托，通过对异常咿包使用核心无状态公平排队算法进行源地址检测并对其处理结果做出相应的处理，可以有效、快速过滤掉异常的IP包数据，提前防止网络受到分布式拒绝服务攻击的侵害。     

VASE: Filtering IP spoofing traffic with agility

Filtering out traffic with forged source address on routers can significantly improve the security of Internet. However, despite intermittent IP spoofing attacks, existing filtering mechanisms inspect each packet all the time, consuming considerable resource on routers even there is no spoofing at all. This article considers the requirement for a solution performing IP spoofing filtering with agility, which consumes resource in proportional to the size of attack. A novel IP spoofing filtering mechanism named Virtual Anti-Spoofing Edge (VASE) is proposed in this article. VASE uses sampling and on-demand filter configuration to reduce unnecessary overhead in peace time. The evaluation based on simulation shows VASE has obvious advantages over commonly used mechanisms in various scenarios. VASE is fully compatible with current IP spoofing filtering practices and can be implemented with commodity routers. In the campus network of Tsinghua University, VASE is providing real benefits.     

Intra domain route optimization for ubiquitous network

The main advantage of a wireless network is user mobility, which calls for efficient routing support at the network layer. An architecture combines hierarchical mobile IPv6 and network mobility for a network mobile and mobile nodes move in tandem and make a hierarchy in the wireless network to management of micro-mobility and seamless handoff. But the capability of the architecture for intra domain route optimization is impaired. So we propose functionality in domain nodes to enable intra domain path optimization for ubiquitous network. It is shown that intra domain cost effect is beneficial in every hierarchical domain that spans mesh network topology. We address the key function for our proposed scheme and analyze the usefulness of our proposed method using mathematically. We show that our proposed scheme performs much better than Network Mobility protocol, especially when the number of mobile nodes or mobile routers or correspondent nodes increases in hierarchically nested in ubiquitous networks.     

无线传感mesh网络的分段地址分配策略及其路由

无线传感器网络中的设备具有能量、缓存空间、通信和计算能力受限的特点。因此,无线传感器网络路由算法需要具备低存储开销、低计算复杂度、无路由发现等特征。HiLow是一种分层路由协议,它完全符合上述特点,且比IEEE 802.15.5具有更好的路由特性。但HiLow存在一些不足,如地址利用率低、仅适用于小规模网络等,无法应用于如环境监测、动物保护等具有较多节点数量和较大网络规模的应用场景。提出了一种两段地址分配策略TFA,它将16位地址分成两段,前段地址用于全功能设备的地址分配,后段地址用于精简功能设备的地址分配。理论分析和数值仿真显示, 相比于HiLow,TFA具有更大的地址利用率和路由树最大深度,能够适用于更大规模的无线传感网络。分析了TFA的mesh路由优化特性,提出了基于TFA的mesh路由算法。仿真结果表明,基于TFA的mesh路由在存储空间使用和能耗等方面都优于IEEE 802.15.5。