CHAPTER 2 WIRELESS MESH NETWORKS

Transcription

1 CHAPTER 2 WIRELESS MESH NETWORKS 2.1 Architecture of Wireless mesh networks Wireless mesh networking is a recent networking paradigm to fit to the growing trend of broadband ubiquitous networking with its capability to support a wide range of application scenarios. End users can experience high speed service delivery as wireless mesh networks rely on multi-hop wireless backbone for data delivery without the need to deploy any fixed infrastructure. Wireless mesh network is an extension of wireless networks. Wireless mesh network is the new network infrastructure for both urban and rural areas for broadband connectivity. Mesh networks reduce the use of cabling to connect the neighboring nodes. In mesh networks there exists a point to point connection between the nodes but it is different from Ad Hoc by the fact that, in Ad hoc network there exist single path between any two nodes but in mesh networks there exists multiple paths between the nodes. [12]. The IEEE standard for wireless mesh networks is s. The main advantage of wireless mesh networks is that, it connects two nodes using multiple paths which provide reliable infrastructure to transfer huge denser data like multimedia content. But we need to invest huge money for creating wired mesh infrastructure for the application environment like covering cities, metro stations etc. The mesh networks are the best methodology for achieving broad band services. They have the ability to self-configure and self-organize. Wireless mesh networks consists of three types of nodes namely mesh routers, mesh clients and gateways. Each node can operate both as host and router. Mesh routers generally show minimum mobility and form the backbone of wireless mesh networks. The clients in wireless mesh networks are either stationary or mobile. A mesh router is usually equipped with multiple wireless interfaces built on either the same or different wireless access technologies. Due to this feature the flexibility is increased. Wireless 9

2 mesh router achieves the same coverage that could be achieved with a conventional wireless router with less transmission power. Some of the mesh routers serve as points for Internet connectivity and are called as Gateways. The nodes receive Internet connection through multi-hop communication. Mesh clients can also work as router. But the functionality of bridge or gateways does not exist in mesh client nodes. Additionally mesh clients have only one wireless interface in contrast to the mesh routers which are equipped with multiple wireless interfaces. Due to their unique characteristics wireless mesh networks have a wide range of applications. The wireless mesh networks provide support for applications that are not possible with other existing wireless networks such as cellular networks, wireless sensor networks, ad hoc networks etc. Wireless mesh networks find applications in wireless broadband services, community networking, instant surveillance systems, high speed MANs, intelligent transportation systems, transient networks in convention centers, disaster recovery and backhaul service for large scale wireless sensor networks. On the basis of node functionality the WMNs may be categorized under three groups: Infrastructure/Backbone WMN: In this type of wireless mesh networks (Figure 2.1) the mesh routers form an infrastructure for the clients that connect to them. Various radio technologies may be used to form the infrastructure in addition to the widely used IEEE technology. As the mesh routers have gateway functionality the routers may be connected to the Internet. This infrastructure network enables integration of WMNs with existing wireless networks. If the same radio technology is used in both the clients and the mesh routers direct communication among them is possible. In situations where the radio technology of the client is different from that of the router, clients communicate with the base stations that have Ethernet connections to mesh routers. Typical application of infrastructure meshing is the community networking. 10

3 Internet Figure 2.1 Infrastructure/Backbone Wireless mesh network 11

4 Client WMN: In client WMNs as depicted in figure 2.2 the client nodes organize themselves into architecture to provide Internet access through store and forward operations. This type of architecture is suitable for indoor environments. Due to scalability problems this is not suitable for metropolitan level networks. Mesh Client Mesh Client Mesh Client Figure 2.2 Client Wireless mesh network Hybrid WMN: This type of architecture (Figure 2.3) combines the features of both Infrastructure and client WMNs. Mesh clients can access the network through mesh routers as well as directly meshing with other mesh clients. While the infrastructure provides connectivity to other networks such as the Internet, Wi-Fi, WiMAX,cellular, 12

5 and sensor networks, the routing capabilities of clients provide improved connectivity and coverage inside the WMN. Internet Figure 2.3 Hybrid Wireless mesh network 13

6 On the basis of number of the available number of channels and number of radios the wireless mesh networks are classified into Single Radio Single-Channel Wireless mesh networks and Multi-Radio Multi-Channel Wireless mesh networks. Single Radio Single Channel Wireless Mesh networks: This is the most basic type of wireless mesh network. Only one radio is present in every node of the network and all the nodes radio interfaces are tuned to the same frequency channel. Due to the existence of only a single channel there will be more interference among mesh routers which is a major performance degradation phenomenon. Multi Radio Multi Channel Wireless Mesh networks: In this type of wireless mesh networks each node in the network is equipped with multiple radios. This feature enables to maintain a large number of concurrent connections. As there is more than one radio the radio interfaces are tuned to nonoverlapping channels and hence interference is minimized. The channel assignments may be static in which the radio interfaces are permanently tuned to a fixed channel or dynamic in which the interfaces can be switched to different channels as the load in the network varies or a combination of the two wherein some of the interfaces are permanently assigned a fixed channel while others dynamically switch channels. The nodes that are assigned a fixed channel permanently in the hybrid assignment strategy are known as the control channels. 2.2 Communication Technologies for Wireless mesh networks Wi-Fi (IEEE x) and WiMax(IEEE x) are the two significant technologies to provide backhaul wireless internet to enable broadband wireless access to cover large areas technologies that operate in the license-free zone is the widely used communication technology for wireless mesh networks. Multiple Access points are interconnected wirelessly to construct a backhaul wireless network and hence wireless coverage to large areas can be achieved. Each Access Point acting as a router 14

7 accepts user connections in its coverage region and routes the data wirelessly to other nodes in a multi hop fashion. Due to the availability of cheap off-the-shelf standard products is a cheap technology for small deployments. Besides the above mentioned advantages technologies also have the following disadvantages. Firstly, a large number of users share the bandwidth. Secondly, significant delay and jitter is apparent as the data rate is limited. Thirdly, QoS provisioning is difficult as operates on probabilistic access mechanism. IEEE standard, the commercial name of which is known as WiMax(Worldwide Interoperability for Microwave access) is used to provide wireless broadband connectivity to metros as IEEE standard is predominantly used to offer data services within a small geographic region. The original design comprised of a central base station that serves fixed subscribers. With the introduction of an additional feature by name mesh mode in the current ( ) standard the subscribers are controlled by the mesh base station that acts as the mesh back bone. Although mesh is advantageous over it is not possible to achieve end to end QoS as the mesh mode only defines per-link and per-hop QoS. In figure 2.4 the architecture of a WiMax communication technology is depicted. 15

8 Figure 2.4 A Wi-Max Network 16

9 2.3 Features of Wireless mesh networks Self organizing and self configuring: The self configuring feature of wireless mesh networks enables the addition and removal of nodes from the network when needed without any administrative intervention. The network topology change is handled by the mesh routing protocol. Self healing: The self healing property of WMNs enables non disruption of service even in situations of node or route failure as there exists a number of alternate routes to transport the data. The degree of meshing influences the capability of self-healing characteristic of WMNs. With the increase in node density the extent of contention is also increased. Hence meshing has to be done optimally. Rapid Deployment: Mesh nodes can be deployed quickly as they do not have strict architectural constraints as against the WLANs that require wired connections of APs to the wired access network. Coverage Extension and Scalability: The multi-hop routing capability of the wireless mesh network enables significant increase in the range to cover large areas whereas scalability is an issue in traditional wireless LANs as they require wired connection for every Access Point. 2.4 Traditional Wireless Multi-hop Networks Vs Wireless Mesh Networks Wireless sensor networks and mobile Ad hoc networks are the most popular wireless multihop networks. Nodes in wireless sensor networks and Ad hoc networks are battery operated. Energy conservation is an issue which of primary concern in wireless sensor networks. This energy constrained characteristic of wireless sensor networks necessitates the need for reduced transmissions and collaborative sleeping mechanisms. Similarly the nodes in Ad hoc networks are predominantly mobile due to which routing and QoS issues are the greatest challenges. Mesh networks on the other hand consists of nodes in the backhaul which are minimally mobile and not energy constrained. Hence the 17

10 existing solutions that address the QoS and routing issues of the wireless multihop networks can be reevaluated and applied in WMNs to achieve optimum performance. Mesh networks in which the nodes are sometimes equipped with more than one radios have larger capacity than the conventional Ad hoc or wireless sensor networks wherein the nodes are usually equipped with a single radio. The nodes in wireless mesh networks are usually relays against the wireless sensor networks and mobile ad hoc networks in which the nodes are used as user terminals in majority of scenarios. Hence the nodes in wireless mesh networks act as Access points to users and user networks. Hence the nodes in wireless mesh networks have more powerful functionalities in comparison with the conventional user terminals. More memory and special routing functions are some of the powerful features present in wireless Mesh nodes. 2.5 Wireless mesh networks: Application Scenarios Due to their rapid commercial deployments, many research activities are underway in wireless mesh networks. As on date many companies are active in wireless mesh networks deployments. Many universities and research centers are showing interest in experimental testbed deployments. Let us take a quick look at some of the application scenarios of wireless mesh networks which cannot be supported by other wireless networks. Community networking using Wireless mesh networks: By Community networking, here we mean a system that is developed to support geographical communities using computers. In the context of community networking, clusters of linked and city wide networks are built by exploiting the wireless technologies. Figure 2.5 provides an illustration of community networking using wireless mesh networks. 18

11 Figure: 2.5 WMNs for community networking 19

12 Wireless mesh networks in Broadband home networking The location of the access point is a major problem in the context of broadband home networking if done using technologies. Conducting site survey to fix the access point or installing many access points to avoid dead zones of service coverage is expensive. Hence by replacing access points with wireless mesh routers, communications among the nodes are flexible and robust. The problem of dead zone can be eliminated with the addition of mesh routers or locating the mesh routers at different places at different times and by adjusting the power level of the mesh routers. Hence with these abilities WMNs can be used to build efficient home networks. Figure 2.6:WMNs for broadband home networking 20

13 Enterprise Networking by using Wireless Mesh Networks An enterprise network may be defined as a network among a few devices in an office or a fairly large network in which a reasonable number of devices in all the offices of a single building are connected or a large network that connects the devices of an office in situated in different locations. Without the use of mesh network technology connectivity among devices in which the networks stand as isolated islands is achieved using technologies wherein wired connections connect the wireless networks at different locations. The need for wired connections makes the use of enterprise networks costly. In such a set up even if the number of backhaul modems is increased with an objective to increase capacity, the problems of link failures and network congestion cannot be nullified. Instead, mesh backhaul enables all nodes to share all the modems in the backhaul which in turn increases the enterprise networks robustness and resource utilization. Also the performance of the enterprise network is not affected by the increase in size of an enterprise network due to the self-organizing and self-configuring property of WMNs. In figure 2.7 an illustration of enterprise network using wireless mesh technology is shown. 21

14 Figure 2.7:WMNs for enterprise networking 22

15 Wireless Mesh Networks as Metropolitan Area Networks: As the physical layer transmission rate of a node in WMNs is very high when compared with any other cellular networks, establishing Metropolitan Area Networks using wireless mesh networking architecture is a good alternative. Figure 2.8:WMNs for Metropolitan Area Networks 23

16 Wireless Mesh Networks in Transportation systems: With the establishment of a mobile mesh network within a vehicle and a high speed mobile backhaul from a vehicle, mesh networks can be used to provide connectivity in buses, ferries and trains whereas and access is limited to stations and stops. Remote monitoring of in-vehicle security video, more efficient passenger information services and driver communications are some of the benefits that could be realized with this application of mesh networks in transportation systems that is not possible with or based wireless networks. Figure 2.9:Wireless mesh networks for transportation systems 24

17 Wireless Mesh Networks in Health and medical systems: In a health care environment, transmission of collected or monitored data for processing or other purpose from one room to another is achieved through the use of broadband facility as most of data is high resolution images. Wireless mesh networks fit well in such a scenario as the Wi-Fi solution relies on the existence of Ethernet connections which turns out to be expensive. Even if traditional wired networks are chosen for such a scenario certain fixed medical devices can be provided only with limited network access. Wireless Mesh Network in Building Automation A building usually consists of several electrical devices that includes power, light, air conditioner, elevator etc.at several situations there may be a need to control and monitor these devices. Presently this controlling is done by using wired networks. Deploying and maintaining a wired network is complex and expensive. Reduction in cost may be achieved to some extent by using Wi-Fi networks. As Wi-Fi networks needs wiring of APs this remains a sub optimal solution to achieve building automation. Deployment cost could be considerably reduced by replacing the APs with mesh routers as shown in figure

18 Figure 2.10: WMNs for building automation Wireless mesh networks in Security Surveillance Systems: Wireless mesh networks are a good choice to support security surveillance as wireless mesh networks can be deployed easily in which ever location of shopping malls or enterprise malls or any other needed location. 2.6 Research Areas in Wireless Mesh Networks The capacity of WMN is dependent on a variety of factors including number of nodes in the network(node density),type of the traffic that traverse the network, the topology of the network, number of channels employed in a node, mobility of the nodes, node s transmission power level etc. A thorough understanding of the influence of the above said factors on the network capacity is essential for protocol development, network deployment, network operation and architecture design. Several researches have been carried out in analyzing the capacity of ad hoc networks which can be adopted to estimate the capacity of WMNs. One such effort is by authors in [39].The authors in [39] have proved that, it is possible to reach the optimum transmission power level of a node when the node has six neighbors. With this value, an optimum tradeoff is achieved between the number of hops 26

19 from source to destination and the channel spatial-reuse efficiency. This suit well for infrastructure wireless mesh networks where nodes are minimally mobile. The authors in [91] have presented an analytical lower and upper bounds of capacity. From this analytical view it is understood that the network throughput decreases if the density of nodes is increased. An important implication by the authors in [91] is that improvement in capacity can be achieved when nodes communicate only with its neighbors. This solution to achieve capacity improvement suggests the deployment of relay nodes and grouping the nodes and forming clusters. Hence communication with a node that is far apart is achieved via relay nodes or clusters. Installation of relay nodes in turn tends to increase the cost of the network. Also management of clusters in a distributed environment is comparatively difficult. Hence the authors in [91] proposed the use of hybrid architecture to achieve capacity improvement. In this structure, if a node wants to communicate to a node that is so many hops away the data packets are sent to the base station or an AP. The AP relays the data to the destination via wired networks. The authors in [34] suggested employing node mobility as a means to improve capacity. In this approach as per the authors the nodes communicate only with its nearby nodes. Hence by moving destination/source near the source/destination communication between source and destination is achieved. Although capacity improvement is evident, this approach suffers from the drawbacks of high transmission delay and the need for a larger buffer at the nodes. Network capacity analysis is a major research challenge in wireless mesh networks. The dependence of ad hoc networks capacity on node density may not be directly applicable in wireless mesh networks. This is an issue to be researched in greater depth. The number of channels is not considered for analysis of network capacity. New research as to prove the optimum number of channels to be present in a node to achieve higher network capacity gains importance. In recent years capacity improvement in wireless networks is achieved with the inclusion of physical layer techniques such as OFDM and UWB techniques. OFDM and UWB techniques enabled high transmission rates. However UWB could be applied only to short distance applications like WPANs.In order to get a transmission speed as that in 27

20 UWB in wide area networks like WLANs or WMANs more efficient physical layer techniques are needed. MIMO techniques offered some capacity improvements along with immunity to fading, delay spread and co channel interference. The usage of antenna diversity and smart antennas in WMNs need to be researched further. The use of directional antennas challenges the performance of MAC protocol. This area needs much research attention. Also the need to estimate channel state information (CSI) for use in smart antennas complicates the process. The spectrum allocated by FCC for wireless networking solutions is not utilized effectively and nearly 70% of the allocated spectrum remains unutilized [37]. As per the survey by FCC in [37] abundant spectrum is still available for communications. Although programmability is a key feature that enables better utilization of available spectrum, it has to go a long way to reap the fullest usage of spectrum. Hence the open research issues in physical layer include the need to propose a new wideband transmission schemes other than OFDM and UWB. Frequency agile techniques which are in the primitive stage needs further improvement. To make the best use of the proposed physical layer techniques newer MAC protocols have to be proposed. Although there are some MAC Protocols using directional and smart antennas [89,69, 100,32] efficient MAC protocol for multi-antenna systems needs to be researched. Also communication protocols for cognitive radios needs to be researched. Data transmission in WMNs not just affects the nodes that are involved in communication but affects other nodes in the vicinity of the communicating nodes. This happens as WMNs adopt multi hop communication as compared to single hop communication in other wireless networks. This issue necessitates the need for efficient MAC protocol design for wireless mesh networks. Due to the absence of a centralized controller in WMNs the MAC function has to be accomplished in a distributed manner. Due to the self-organizing nature of the WMNs the MAC protocol should have a complete knowledge of the topology changes that occur in the network. The promising 28

21 research issue in MAC layer is to improve the scalability of CSMA/CA protocol. A MAC protocol that considers the heterogeneity of different network nodes is another research issue in MAC layer.mac protocols to support broadband multimedia communication needs further research. Some mesh routers does the function of integrating different wireless technologies. This necessitates the need to develop efficient bridging functions. This is an area that needs to be researched to a greater depth. As WMNs are integrated with the Internet, IP is the network layer protocol for WMNs. Also many of the routing protocols proposed for ad hoc networks are applied to WMNs as these two networks share several common features. Besides the availability of several routing protocols for ad hoc networks, to realize the fullest benefit of WMNs new routing protocols with efficient routing metrics that capture the link quality accurately needs to be proposed. Proposing new cross layer routing protocols for WMNs is an active research area. Also the existing routing protocols must be researched further to address scalability. Routing solutions to accomplish multicast communication is another research area in wireless mesh networks. With regard to the transport layer WMNs do not have a specific transport layer protocol. The transport layer protocols used in other networks applies to WMNs also. The inability of TCP to differentiate between losses that are due to congestion and noncongestion motivated the proposal of new transport protocols for Ad hoc networks. Hence many variants of TCP protocol was proposed to account for the peculiar features of Ad hoc Networks. These variants are applied to WMNs as WMNs and Ad hoc Networks share several common characteristics. Some of these TCP variants include TCP-F,TCP-ELFN,TCP-BuS. Although in TCP-F differentiation between losses due to congestion and that due to channel was made, designing a loss differentiation approach is to be researched. As the ACK plays a crucial role in TCP, the issue gains importance in dealing with link asymmetry. Several solutions, Viz ACK filtering [20] that was proposed to address link asymmetry needs to be investigated further. Certain new transport protocols have been proposed for Ad Hoc networks. ATP-Ad hoc Transport Protocol is one such effort. But for the fact that WMNs are integrated with Internet the idea of an entirely new transport protocol for WMNs is discouraged. This is because the ATP 29

22 mechanism considers the network to be standalone which is not the case in WMNs. Efforts to propose rate control protocols to guide in end to end delivery of real time data needs attention. The necessity to deploy WMNs is determined by the application. Internet access is one of the areas where WMNs are used for among the list of several other applications supported by WMNs. With the growing number of applications to be supported by WMNs, the need to develop novel algorithms for application layer to improve the performance of real time Internet applications need to be researched further. New application protocols to enable peer to peer information sharing are to be developed for WMNS. Protocols for mobility management are another area in WMNs that needs to be researched further. Network management is another issue to be researched. Effective data processing algorithms to detect abnormal operation of WMNs needs to be developed. The aspect of network security is achieved perfectly for many wireless LANs. The security aspects of authentication, authorization and accounting is performed in a centralized manner through RADIUS server(remote Authentication dial-in user service).however as this centralized RADIUS scheme does not account for scalability security is often compromised when such centralized schemes are employed in WMNs. Hence a security method that caters the peculiar characteristics of wireless mesh networks needs to be researched. Key management in wireless mesh networks is a hot research area as there is no central infrastructure or server to manage keys. Also the need to achieve key management in wireless mesh networks in a distributed manner complicates the task of key management. Several protocols in which the security mechanisms are embedded in the routing or MAC protocols were proposed [11, 12].These protocols are not effective for WMNs and the need to propose multi-layer security mechanisms is to be given importance. Also designing a practical system that monitors security in a practical deployment and development of algorithms to detect intrusion are major research challenges in wireless mesh networks. 30

23 2.7 WMN deployments As WMNs has got many special features compared to traditional wireless multi hop networks many companies have done installation for commercial purpose. Several research and nonprofit organizations have also taken efforts to deploy WMNs. In this section let us take a quick look at some these deployments Non Commercial Deployments Roofnet An experimental multi-hop mesh network with 50 nodes operated by Massachusetts Institute of Technology is Roofnet[25].This network is located in Cambridge, Massachusetts. This is a b based mesh architecture.rts/cts is disabled in the wireless cards of the nodes. Modular router click [14] by MIT is used to route the data packets in Roofnet. Every node runs a Web server, NAT and a DHCP server in its Wired Ethernet port. SrcRR is the routing protocol employed in Roofnet. SrcRR employs ETX as the routing metric.etx captures the quality of the link better than the conventional hop count metric. The users are volunteers and they accepted to host the equipment needed to establish mesh connectivity in their dwellings. BWN BWN [2] stands for Broadband and Wireless Network. This is a testbed developed by the Georgia Institute of Technology. The network consisted of 15 nodes. These nodes are mesh routers. The mesh routers operate on wireless technology. Some of these nodes are Gateways to provide Internet connectivity to the nodes. Feasibility evaluation of protocols for heterogeneous networks is carried out at BWN Lab by integrating BWN mesh testbed with Sensor Network testbed 31

24 Figure 2.11:Architecture of BWN-Mesh testbed at Georgia Tech 32

25 Hyacinth Besides the availability of several channels that do not overlap in the 2.4GHz to 5GHz spectrum most of the based wireless technologies use only a single channel. Hence such multi hop networks fail to exploit the total bandwidth provisioned in the standards. Hyacinth [5] is a multi-channel wireless mesh network. The communication technology can be a/b/g or a. Every node in the Hyacinth network architecture is equipped with radios. Interface channel assignment and packet routing are the two central design issues of this multi-channel wireless mesh network. When a node X wants to establish a communication with a node Y, the interfaces of the nodes X and Y has to be assigned to a common channel. However the effective bandwidth available to every interface decreases when many interfaces are tuned to the same channel. This necessitates the availability of an effective channel assignment strategy [78] for optimum performance. The load on each interface is determined by the routing strategy. The hyacinth network consists of 10 nodes.in figure 2.12 the architecture of Hyacinth network is presented. 33

26 Figure 2.12:Architecture of Hyacinth Network 34

27 UCSB UCSB Mesh network [10] is an experimental wireless mesh network testbed with 25 nodes deployed in the University of Calofornia, Santa Barbara. The nodes were equipped with IEEE a/b/g wireless cards. UCSB mesh network is a multi-channel mesh network with the 25 nodes placed across five floors of the campus building. This testbed consisted of two types of nodes namely the gateway nodes and mesh nodes. The Intel Celeron 2.4 GHz machines with Linux version 16 and hostap driver is used as the Gateway nodes. NetGate 2511 PCMCIA b radios are used. The wireless mesh nodes are operated in ad hoc mode. Additionally every node is provided with an Ethernet interface. This aids in providing Internet access to the nodes in the network. Multimedia traffic is traversed to analyze the performance of the network.udp video and voice streams are used as the traffic in the network. AODV is the routing protocol used in the testbed. CUWiN Champaign-Urbana Community Wireless Network(CUWiN)[3] is special project developed by the UCIMC(Urbana Champaign Independent Media Center).This project was started in the year 2000.A group of people took advantage of the underutilized internet links to build a nonprofit community network. All types of equipments ranging from personal computers to specialized Soekris servers are part of this mesh network. Initially Dijkstra s OSPF (open shortest path first) routing method was employed. Later a more appropriate routing protocol by name Hazy sighted Link State (HSLS) was used. Recently a modification to HSLS named A-HSLS (Adaptive Hazy sighted link state routing method is used.etx is the routing metric used in this testbed for routing packets. 35

28 2.7.2 Commercial Mesh Networking Solutions Locust world The LocustWorld [6] Company manufactures mesh routers by name Mesh Boxes. Mesh Boxes work on open source software modules. The MeshBox acts as an AP to relay data packets. Broadband connectivity can be achieved by interconnecting multiple Mesh Boxes. Every node in this mesh architecture is equipped with an b wireless adapter and an Omni directional antenna. AODV is the routing protocol used in Locust World Mesh networks. Linux kernel is used in Mesh Boxes. Every node allocates an address automatically in the range 10.x.x.x.DHCP client on the Ethernet interface is used to find the gateway by the nodes. Microsoft Mesh Connectivity Layer MCL[65] is a loadable windows driver that implements an interposition layer between layer 2 and layer 3.MCL is treated as another Ethernet link by the upper layers.mcl appears to the lower layers as another protocol running above the physical link. Routing is done by LQSR [73] protocol. The routing metric used is WCETT (Weighted cumulative expected transmission time). Firetide Firetide [4] Inc is a private mesh networking company established in the year 2003.Networking devices needed for the quick,easy and affordable deployment of high performance wireless mesh networks are produced by this corporation. Firetide s mesh networking solutions are ideal in building backbone infrastructure for Wi-Fi environments, video surveillance. These are also the ideal choice for establishing temporary networks at locations where wiring is disruptive and difficult. 36

29 Mesh Networks This is a mesh network deployment by Motorola [8] to provide mobile broadband Internet access. QDMA (quad division multiple access) is the radio technology used to provide Internet connectivity to mobile users. An attractive feature of this Motorola Mesh networks is their Mesh Networks Scalable Routing Protocol (MSR) which is proprietary. The hybrid algorithm with the combined features of proactive and reactive routing mechanisms used in MSR, resulted in high speed mobility, low routing overhead and improved scalability. Tropos The Tropos mesh networking solutions [9] includes TroposMesh Operating System and routers built specifically for outdoor and indoor environments. Routing is done by Predictive wireless Routing Protocol(PWRP).The problem of radio interference, failure of backhaul or router failure is avoided due to the usage of PWRP. The routing overhead is very low even when the network is scaled to thousands of nodes. PWRP is the only routing protocol that optimizes client-server throughput. BelAir Networks The mesh network from BelAir Networks [1] is based on a multi-interface approach. Every node is made up of at least three radios. These radios are connected to any one of the eight antennas that forms the backhaul. Manual intervention to align the radio interfaces is not necessary. BelAir networks employ its patented pending auto antenna selection algorithm to map the radios to the antennas in the backhaul. A radio ware routing algorithm in which the best route is chosen on the basis of available capacity and latency is used to transport the traffic in BelAir Networks. 37

30 MeshDynamics MeshDynamics [7] is a mesh network architecture constructed using devices. It is a multi-interface mesh networking solution. In MeshDynamics backhaul and service functionalities are clearly separated. The channels of all the radios are managed dynamically. Hence all radios are located on non-interfering channels. In a 3 radio structure, up link and downlink functionality for backhaul is done using 2 radios. The clients are provided services through the third radio. 2.8 Summary This chapter extensively addresses the architecture of wireless mesh networks, communication technologies for wireless mesh networks, differences between traditional multi hop networks and wireless mesh networks, various application scenarios of wireless mesh networks and various commercial and non-commercial wireless mesh networks deployments around the globe. 38