Securing Wi-Fi networks

Wi-Fi networks, based on the IEEE 802.11 b/g standards, have become very popular in recent years. Many users have installed Wi-Fi networks at home, and numerous corporations have added Wi-Fi access points to their wired networks, giving employees easier access to corporate data and services. Hackers can decrypt and read data on a wireless link protected by built-in WEP encryption, and may even be able to access the data on a wired network through a Wi-Fi access point. We assess Wi-Fi network security in one city, analyze alternative security techniques, and suggest ways to secure such networks.     

Survivable millimeter-wave mesh networks

Millimeter-wave mesh networks have the potential to provide cost-effective high-bandwidth solutions to many current bandwidth-constrained networks including cellular backhaul. However, the availability of such networks is severely limited due to their susceptibility to weather, such as precipitation and humidity. In this paper, we present a rigorous approach to survivable millimeter-wave mesh networks based on experimentation, modeling, and simulation. Individual link performance is characterised using frame error-rate measurements from millimeter-wave transmissions on test links over a period of one year. A geometric model based on radar-reflectivity data is used to characterise rain storms and determine their impact on spatially correlated links of a mesh network. To mitigate the impact of link impairments on network services, we present two cross-layered routing protocols to route around the failures: P-WARP (predictive weather-assisted routing protocol) and XL-OSPF (cross-layered open shortest-path first). We conduct a performance analysis of the proposed mesh network under the presence of actual weather events as recorded by the US National Weather Service. Results show that the proposed approach yields the highest dependability when compared against existing routing methods.     

Load-balanced mesh router migration for wireless mesh networks

Load-balancing among domains in a wireless mesh network (WMN) is normally achieved by changing the Internet attachment of mesh routers (MRs) that carry the traffic from mobile stations (MSs). The greediness of load-balancing algorithms may force MRs to frequently change their Internet attachments, and thus degrade network performance due to inter-domain mobility of the associated MSs. In this paper, we discuss the negative impact on the performance of MSs’ mobility, due to inter-domain reassignment of MR. A MR migration scheme is proposed to achieve a tradeoff between load-balancing and inter-domain reassignment of MR. The proposed load-balancing scheme for WMNs includes: an initialization procedure to divide a WMN into domains, and a load adjustment procedure to rebalance the traffic load among the neighboring domains when required. We also provide a framework for handling inter-domain mobility in support of multi-hop communication using the Multi-hop cellular IP. Our simulation results show that the proposed protocol effectively controls MR’s change in connectivity as well as MS’s mobility.     

Link quality prediction in mesh networks

Wireless self-organizing networks such as mesh networks strive hard to get rid of mobility and radio propagation effects. Links – the basic elements ensuring connectivity in wireless networks – are impacted first from them. But what happens if one could mitigate these effects by forecasting the links’ future states?

In this paper, we propose XCoPred (using Cross-Correlation to Predict), a pattern matching based scheme to predict link quality variations. XCoPred does not require the use of any external hardware, it relies simply on Signal to Noise Ratio (SNR) measurements (that can be obtained from any wireless interface) as a quality measure. The nodes monitor and store the links’ SNR values to their neighbors in order to obtain a time series of SNR measurements. When a prediction on the future state of a link is required, the node looks for similar SNR patterns to the current situation in the past (time series) using a cross-correlation function. The matches found are then used as a base for the prediction. Clearly, XCoPred takes advantage of the occurrence and recurrence of patterns observed in SNR measures reflecting the joint effect of human motion and radio propagation. XCoPred focuses only on the scale of links and as such is complementary to mobility prediction schemes, which target prediction at a broader scale. We first prove the occurrence of SNR patterns resulted by the joint effect of human motion and radio propagation. Then we evaluate XCoPred in an indoor mesh network showing, that XCoPred is able to recognize mobility patterns in up to 85% of the cases correctly and the average prediction error on mid-term predictions (i.e., assessing the future link quality more than 1 min ahead) is less than half the error we get using linear prediction.

Eventually, we propose and evaluate an enhanced handoff management scheme for 802.11 mesh networks showing the usefulness of XCoPred as a cross-layer input.     

Wireless mesh networks based on CDMA

In this paper, we study hybrid contention-free/contention-based traffic management schemes in presence of delay-sensitive and delay-insensitive data in multihop CDMA wireless mesh networks. We suggest a greedy incremental contention-based ordering algorithm for contention-free schedules and also propose a time-scale-based framework for integration of contention and contention-free traffic management schemes. Further, for the contention-free phase, we propose a power control algorithm that gives an end-to-end throughput guarantee. With the aid of simulation, we observe the additional end-to-end throughput that can be achieved when scheduling and tight power control are applied.     

Circuit-switched broadcasting in torus and mesh networks

We consider the problem of broadcasting on torus and mesh networks using circuit-switched, half-duplex, and link-bound communication. In this paper, we obtain an optimal broadcasting algorithm that uses pd time steps for a d-dimensional torus with (2d+1)^p nodes in each side of the torus. Using this algorithm, we show that a broadcasting on a d-dimensional mesh with the same size can be done in pd+p+d-1 time steps     

Efficient path-based multicast in wormhole-routed mesh networks

The capability of multidestination wormhole allows a message to be propagated along any valid path in a wormhole-routed network conforming to the underlying base routing scheme. The multicast on the path-based routing model is highly dependent on the spatial locality of destinations participating in multicasting. In this paper, we propose two proximity grouping schemes for efficient multicast in wormhole-routed mesh networks with multidestination capability by exploiting the spatial locality of the destination set. The first grouping scheme, graph-based proximity grouping, is proposed to group the destinations together with locality to construct several disjoint sub-meshes. This is achieved by modeling the proximity grouping problem to graph partitioning problem. The second one, pattern-based proximity grouping, is proposed by the pattern classification schemes to achieve the goal of the proximity grouping. By simulation results, we show the routing performance gains over the traditional Hamiltonian-path routing scheme.     

多信道无线Mesh网络的路由协议

针对单径路由协议不能充分利用多信道无线Mesh网络的信道资源的问题,提出了一种基于拥塞控制的并行多径路由协议PMRP。该协议将一个数据流分配到多条路径同时传输,当所有路径都发生中断时,才重新寻找路由;并采取相应的拥塞感知技术,避免拥塞节点再转发新的数据流。仿真结果证明：与无线自组网按需平面距离矢量路由协议（AODV）协议相比,PMRP在网络负载较大时,能有效地减小端到端延迟,提高数据包的成功投递率,增加网络的整体吞吐量。     

一种改进的ZigBee mesh网络路由算法

针对ZigBee mesh网络中传统AODVjr路由算法耗能较高的问题,提出了一种改进算法。该算法基于节点角色差异性和节点当前能量状态进行路由发现,从而避免了一些关键节点或能量偏低的节点在信息传送时由于继续大量耗能而成为失效节点,造成某条路径的失效甚至整个网络的瘫痪。结果证明,改进算法提高了网络传输的可靠性,节约了网络的总体能耗,延长了网络的生命周期。     

Realistic propagation simulation of urban mesh networks

Simulation plays an important role in the verification of mobile wireless networking protocols. Recently, several cities have either begun deploying or are completing plans to deploy large-scale urban mesh networks (LUMNets). On the other hand, the networking research community has little expertise in simulating such networks. While the protocols are simulated reasonably realistically, the propagation of wireless transmissions and the mobility of nodes are not. Today, simulations typically model propagation with either the free-space model or a “two-ray” model that includes a ground reflection. Such models are only valid in open space where there are no hills and no buildings. Since wireless signals at the frequencies used for mobile wireless networking are partly reflected off of buildings and partly is transmitted into the building, the presence of buildings greatly influences propagation. Consequently, the open-space propagation models are inaccurate in outdoor urban areas. Indoors, the open-space models are not even applicable. This paper presents guidelines for simulating propagation in such urban settings. Extensive background discussion on propagation is also included. The techniques for propagation are validated against propagation measurements. The techniques discussed are implemented in a suite of tools that are compatible with protocol simulators and are freely available for use.     

Using genetic algorithms to design mesh networks

Designs for mesh communication networks must meet conflicting, interdependent requirements. This sets the stage for a complex problem with a solution that targets optimal topological connections, routing, and link capacity assignments. These assignments must minimize cost while satisfying traffic requirements and keeping network delays within permissible values. Since such a problem is NP-complete, developers must use heuristic techniques to handle the complexity and solve practical problems with a modest number of nodes. One heuristic technique, genetic algorithms, appears to be ideal to handle the design of mesh networks with capability of handling discrete values, multiobjective functions, and multiconstraint problems. Existing applications of genetic algorithms to this problem, however, have only optimized the network topology. They ignore the difficult subproblems of routing and capacity assignment, a crucial determiner of network quality and cost. This article presents a total solution to mesh network design using a genetic algorithm approach. The application is a 10-city network that links Hong Kong and nine other cities in China. The development demonstrates that this method can be used for networks of reasonable size with realistic topology and traffic requirements     

Efficient load-balancing routing for wireless mesh networks

Wireless mesh networks (WMNs) consist of static wireless routers, some of which, called gateways, are directly connected to the wired infrastructure. User stations are connected to the wired infrastructure via wireless routers. This paper presents a simple and effective management architecture for WMNs, termed configurable access network (CAN). Under this architecture, the control function is separated from the switching function, so that the former is performed by an network operation center (NOC) which is located in the wired infrastructure. The NOC monitors the network topology and user performance requirements, from which it computes a path between each wireless router and a gateway, and allocates fair bandwidth for carrying the associated traffic along the selected route. By performing such functions in the NOC, we offload the network management overhead from wireless routers, and enable the deployment of simple/low-cost wireless routers. Our goal is to maximize the network utilization by balancing the traffic load, while providing fair service and quality of service (QoS) guarantees to the users. Since, this problem is NP-hard, we devise approximation algorithms that provide guarantees on the quality of the approximated solutions against the optimal solutions. The simulations show that the results of our algorithms are very close to the optimal solutions.     

Coordination problem in cognitive wireless mesh networks

Due to their potential to create and extend pervasive communication applications to cognitive environments with distributed control, the emerging technology of cognitive wireless mesh networks is gaining significant attention from a growing research community. However, the major challenge in cognitive networks is the adaptation to time and space variability of the available resources, namely chunks of the frequency spectrum called channels. In particular, this problem is exacerbated in cognitive mesh networks because there exists no direct communication among devices which thereby cannot establish a global (common) control channel to coordinate the entire network. Instead, only local control channels that vary depending on the time instant and location, can be established to coordinate cognitive devices among themselves. This paper first analyzes the underlying challenges and existing approaches to address the absence of a static and global control channel, and then propose a novel Control channel formation protocol, called Connor. Our protocol Connor is a fully distributed coordination scheme where cognitive mesh devices self-organize into clusters based on the similarity of available channels and on topological constraints. Compared with the existing clustering algorithms, which requires synchronization, the proposed Connor performs better in most cases without imposing synchronization.     

无线mesh网中网关部署的优化设计

无线mesh网中的流量经路由器聚集后主要是通过少量网关至因特网的,容易在网关处形成导致网络性能的瓶颈。针对此问题,首先对网关和路由器作等效节点化处理,利用无线通信阴影效应的对数-正态分布模型,设计加权目标函数保证节点的连通性和覆盖率,得到候选网关节点的位置部署;在此基础上根据网关部署的约束条件和网络生成连通图,设计启发性基于度/权值的树集分割（TSP）算法,选择出满足吞吐需求、有较好连通性的候选节点担任网关设置。NS2仿真结果验证了该设计方法对改善网关节点的吞吐容量和信号覆盖连通率的有效性。     

骨干无线网状网的排队延迟性能研究

对一种基于网状分布的骨干无线网状网的延迟性能进行研究.提出了一种基于均衡负载的最短路径路由协议.在此协议基础上,研究了无线网状网数据包的排队延迟,推导出无线网状网排队延迟与网络的规模、网关和网状路由器的服务能力、数据包到达率的相互关系.此外,还分析排队延迟和网络容量的相互制约关系,并给出了在延迟限制条件下的网络容量.     

Channel allocation in multi-channel wireless mesh networks

In this article, we survey the latest progress in multi-channel wireless mesh networks, focusing on wireless interference models and channel allocation algorithms with the goal of maximizing the network performance. We present the studies of different interference models and illustrate how they could affect the design of channel assignment. We also summarize channel allocation algorithms with different strategies in both omni-directional and directional antenna networks. We conclude that both static and dynamic channel allocation strategies have advantages and disadvantages, and the design of channel allocation algorithms strongly depends on the interference model and the assumption of network traffic.     

无线保真度

Wi-Fi是无线保真度(Wireless　Fidelity)的缩略 语,它是基于电气和电子工程师协会IEEE　802.11协议 的一组无线局域网(WLAN)规格标准。 Wi-Fi 原打算用于无线设备与局域网的连接,但现 在经常用于接入因特网。当距离一个被称为“热点”的接 入点较近时,每个人都可以将具有无线联网能力的计算 机或个人数字助理(PDA)连接到因特网。 被认证的产品可以使用正式的Wi-Fi 徽标,表明该 产品能够与任何带有此徽标的其他…     

A dynamic channel reservation method for multimedia streaming in Wi-Fi Mesh networks

To improve data transmission robustness in the Wi-Fi Mesh standard, a deterministic channel access method was added to the basic random access method, which enabled the stations to get a contention-free access in the previously reserved time intervals. This mechanism can be conveniently used for transmission of the real-time multimedia streams which require quality-of-service support. However, the packet transmission in the reserved time intervals is affected by random noise and interference, and the time-consuming reservation procedure does not allow one to change on-the-fly the amount of reserved channel resources. A method for dynamic channel reservation which takes into account these aspects of the deterministic channel access mechanism and meets the quality-of-service requirements was proposed.     

无线Mesh网络路由协议的研究进展

在简要介绍无线Mesh网络特性的基础之上,对路由协议中若干关键技术的研究状况进行了总结和综述,重点讨论面向无线Mesh网络的路由度量的设计思路、多信道多无线接口环境下节点的自适应信道分配策略以及结合无线介质的广播特性的寻路算法的分析.详细讨论了上述因素对于路由协议性能的具体影响,深入分析了当前研究的优缺点.同时,鉴于无线链路上传输的不可靠和高误码率,详细介绍了跨层协议设计的相关内容.