ESTRUCTURA NARRATIVA EN EL DISCURSO ORAL DE

WMNs have emerged as a promising technology for next-generation net- working. In WMNs, no cabling is required to connect the mesh routers. All mesh routers self-configure wirelessly to form a rich radio mesh back- bone network. The wireless connectivity between routers significantly re- duces the deployment and maintenance cost when compared with wired networks. Due to these attractive features of WMNs, they are considered for a wide variety of applications such as community networking, emer- gency operations, home networking, and hybrid wireless architectures. In this chapter, the major issues and applications of WMNs were described.

The design issues and deployment scenarios were also discussed. Provid- ing high throughput is the major design goal of WMNs, which has been addressed in multiple layers. To improve the performance of WMNs, the multi-channel, multi-radio architecture has been suggested. The related pro- tocols for this architecture in MAC and routing layer were discussed. Some routing metrics were described to find high-throughput paths by taking into account the channel quality and inter flow and intra flow interference. Security and standardization are the main concerns for the wide deploy- ment of WMNs. Some of the security issues and standards such as IEEE 802.11s and IEEE 802.16 mesh were also discussed. Finally, to provide in- sight on real implementations of WMNs, some WMN testbeds and mesh networking products were also discussed.

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Chapter 2

Mesh Networking in

Wireless PANs, LANs,

MANs, and WANs

Neila Krichene and Noureddine Boudriga

Contents

2.1 Introduction . . . .47

2.2 Wireless Mesh Networking Fundamentals . . . .48

2.2.1 Network Architecture . . . .48 2.2.2 Characteristics . . . .49 2.2.3 Supported Applications . . . .50 2.2.4 Routing Protocols . . . .51 2.2.5 Network Management . . . .52 2.2.6 QoS Provision . . . .53 2.2.7 Security Considerations . . . .55 2.2.8 Scheduling and Multimedia Support . . . .55

2.3 Wireless Mesh PANs . . . .56

2.3.1 Background and Objectives . . . .56 2.3.2 Challenges . . . .56 2.3.3 Architecture . . . .57 2.3.4 The IEEE 802.15.5 Standard . . . .57 2.3.4.1 Meshing and the Ultra Wide Band . . . .58 2.3.4.2 Overview of the ZigBee IEEE 802.15.4 Standard . . .59 2.3.4.3 IEEE 802.15.4 Physical Layer . . . .59

2.3.4.4 IEEE 802.15.4 MAC Layer . . . .59 2.3.4.5 Overview of the IEEE 802.15.5 Standard . . . .60 2.3.4.6 Routing and QoS Support . . . .62

2.4 Wireless Mesh LAN . . . .65

2.4.1 Introduction and Advantages . . . .65 2.4.2 Architecture Technologies . . . .67 2.4.3 Challenges . . . .68 2.4.4 The IEEE 802.11s Standard . . . .68 2.4.4.1 IEEE 802.11s Device Classes . . . .69 2.4.4.2 Medium Access Control: The Medium

Access Coordination Function . . . .70 2.4.5 Routing and QoS Support . . . .73 2.4.5.1 WMR Protocol Overview . . . .73 2.4.6 Overview of Available Commercial Systems . . . .77

2.5 Wireless Mesh MAN . . . .78

2.5.1 Purpose . . . .78 2.5.2 Targeted Services . . . .78 2.5.3 Architecture . . . .79 2.5.4 Standards . . . .80 2.5.4.1 MAC Layer Overview in WiMAX Mesh Mode . . . .81 2.5.4.2 Hand-Over . . . .85 2.5.4.3 Physical Layer Overview in WiMAX

Mesh Mode . . . .86 2.5.4.4 QoS Support . . . .86 2.5.5 Deployed Solutions . . . .90

2.5.5.1 Tropos® Networks . . . .90

2.5.5.2 Strix Systems . . . .93

2.6 Wireless Mesh WAN . . . .94

2.6.1 IEEE 802.16 Mobility Management . . . .95 2.6.2 IEEE 802.20 . . . .96 2.6.2.1 802.20 PHY Layer . . . .96 2.6.2.2 802.20 MAC Layer . . . .97 2.7 Advanced Issues . . . .99 2.7.1 Physical Layer . . . .99 2.7.2 MAC Layer . . . .99 2.7.3 Network Layer . . . 100 2.7.4 Transport Layer . . . 100 2.7.5 Application Layer . . . 101 2.7.6 Network Management . . . 102 2.7.7 Security . . . 102 2.8 Conclusion . . . 103 References . . . 104

Wireless mobile mesh networks are made up by several mobile nodes, fully wirelessly interconnected, which adopt multi-hop communication for data transmission. This chapter intends to argue why mesh networking technology represents a new issue to address for wireless networks by pre- senting the mesh networking fundamentals in wireless PANs, LANs, MANs, and WANs. For this purpose, we will first study the mesh networking charac- teristics while stressing the targeted applications, the network architecture, and the particularities of the routing, quality of service (QoS) provision, and management protocols. Then, details of the IEEE standardization efforts tar- geting the network coverage ranging from PANs to WANs are presented. We conclude by presenting some of the deployed solutions and discussing advanced design issues aiming at providing scalable, low-cost, and easily deployable Wireless Mobile Mesh Networks.

2.1 Introduction

The mobile ad hoc networks (or MANET) have gained researchers’ atten- tion for 30 years [1]. MANET nodes share wireless links and can play the role of client and router at the same time without relying on any infras- tructure; thus accomplishing large deployment ease and investments cost decrease. Besides, the ephemeral nature of MANETs particularly copes with critical applications such as disaster recovery and battlefield communica- tions. Many research works have addressed the multi-hop communication issue in wireless networks, but the practical impact was not very impor- tant because users rarely operate in ad hoc mode. For instance, the targeted applications were limited to specialized missions inducing an unreasonable cost, while users searched mostly for cheap information sharing and Inter- net access. Client satisfaction has created a new research topic that aims at revising the MANET concept by considering the MANET network as a flex- ible and low-cost extension of wired infrastructure networks that integrates them. As a result, the wireless mesh networking paradigm, which inherits some MANET characteristics and targets civilian applications, was born. It is worth noticing that both the wired Internet and the public switched telephone network may be classed as mesh networks [2]; however, future wireless mesh networks should rely on a wireless infrastructure to inter- connect mobile devices in a multi-hop fashion. Wireless mesh networks (WMNs) support home and enterprise networking applications; they also provide ubiquitous Internet access and enable the implementation of intelli- gent transportation systems and public safety applications. Besides, their deployment does not require important investments comparable to the deployment of wired solutions. In fact, wireless mesh routers can rapidly

and easily integrate the wireless infrastructure as soon as the coverage needs to be extended. As a result, a growing number of cities have adopted this paradigm to attract visitors and citizens and start a long-lasting devel- opment process. Users can temporarily join the mesh network and act as clients and routers for other nodes, thus enhancing the network capacity, throughput, and reliability. Currently, one can find off-the-shelf and propri- etary mesh networks solutions while IEEE standardization efforts are target- ing network coverage ranging from PANs to WANs. The goal of this chapter is to present the mesh networking fundamentals in wireless PANs, LANs, MANs, and WANs. To this end, a general overview of the mesh networks architecture and characteristics is given while addressing general concepts such as the supported applications, the routing and management protocols, the QoS provision, and the security considerations. Then, the detail of the IEEE standardization efforts targeting the network coverage ranging from PANs to WANs is presented. We particularly address the physical layer and the MAC layer design issues for the mesh communication mode support while presenting the challenges that are particular to each network (PAN, LAN, MAN or WAN). An overview of the available commercial systems and deployed solutions is also given. We conclude by discussing some of the re- search issues aiming at designing scalable, low-cost, and easily deployable wireless mobile mesh networks.

2.2 Wireless Mesh Networking Fundamentals

2.2.1 Network Architecture

A wireless mesh network is a hierarchical network formed by fully wire- lessly interconnected nodes, as illustrated in Figure 2.1. A fully meshed network is a network where every node directly connects to every other node; a partial mesh network is a network where each node is connected to a set of other nodes [47]. We distinguish routers nodes that act as layer 3 gateways and support meshing functions. Such nodes are usually equipped with multiple network interfaces for different access technologies; they can guarantee wider coverage with less power consumption thanks to the sup- port of multi-hop communications. The network resulting from the mesh routers interconnection is called a wireless backbone; it guarantees the con- nectivity between nomadic users and wired gateways. The wireless mesh network includes also Access Points (APs), which can be viewed as special mesh routers provided with a high-bandwidth wired connection to the Internet. The wireless network formed by the interconnection of the AP and the mesh routers is called a backhaul. The latter enables the access to external networks while providing high-bandwidth and seamless multi-hop communication at a low cost.

Wired Internet backbone Access points Wireless routers Nomadic users

Wired/Wireless connection Wireless connection Figure 2.1 The wireless mesh network architecture.

Finally, mesh clients are generally equipped with a radio interface sup- porting mesh networking functions; that is why they can act as routers for other mesh nodes. However, they do not provide the bridge/gateway functionalities needed for Internet access and interoperability with other networking technologies. Mesh clients can be laptops, pocket PCs, PDAs, IP phones, etc.

2.2.2 Characteristics

Mesh networks are gaining a growing interest thanks to their special char- acteristics that enable the deployment of new applications at lower cost. The most important characteristics are as follows:

Multi-Hop Communication: The multi-hop communication scheme

guarantees larger coverage zones and an enhancement of the net- work capacity. In fact, line-of-sight constraint no longer matters because the intermediate nodes relay the information to their neigh- bors on short wireless links using a reduced power transmission. As a result, the interferences are decreased and the throughput is

augmented [3]. Besides, the multi-hop connectivity allows several devices to access the network at once by relying on other mesh nodes without affecting the overall network performance. Finally, mesh networks gain more capacity as the number of internal nodes increases and the data traffic can reach larger areas by crossing mul- tiple hops until the final destination.

Wide Coverage and Cost Reduction: The wireless infrastructure sup-

ported by the mesh networks eliminates the deployment costs of a new wired backhaul through cities and rural areas. Moreover, the flexible infrastructure can easily be enforced by adding new wireless mesh routers anywhere, anytime the coverage needs to be enhanced. Only some APs need to be connected with the wired infrastructure to allow Internet access.

Self-Configuration and Self-Management: New mesh nodes that

enter the network are transparently supported because meshing functions such as neighbors discovery and automatic topology learn- ing are implemented. Wireless routers rapidly detect the presence of new paths, thus enhancing the overall performance and coverage.

Network Access and Interoperability: Backhaul devices are equipped

with multiple network interfaces that support both Internet and peer- to-peer communications while guaranteeing access to existing wire- less networks technologies such as traditional IEEE 802.11, WiMAX,

ZigBeeTM_{, and cellular networks.}

Mobility and Power Consumption: The mobility and power consum-

ption vary with the nature of the mesh node. For example, mesh routers and APs have minimal mobility and reduced power con- straints. However, mesh clients are mostly small mobile devices with reduced battery autonomy. Therefore, MAC and routing proto- cols supported by the backbone/backhaul do not need to be power efficient, but they cannot be implemented on simple mesh clients.

Reliability: Mesh networks rely on multi-hop communication and

can use every internal node to route traffic to the destination. There- fore, multiple paths exist between two communicating endpoints and temporary path failures can be easily tolerated. Besides, mesh clients that need to communicate with external destinations (e.g., Internet) can choose between multiple egress points toward the wired network, thus tolerating router failures and reducing potential congestions.

2.2.3 Supported Applications

The mesh networks support a large number of applications dedicated to personal, local, metropolitan, and wide areas networks.

Home Networking: Mesh networks can be deployed at home because they support bandwidth-greedy applications such as multi- media traffic transmission [5]. Mesh nodes can be desktop PCs, lap- tops, high-definition TV, and DVD players. Wireless APs or mesh routers can easily be added to cover dead zones without requiring