02-11-2012, 03:24 PM
WIRELESS MESH NETWORK
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Introduction to wireless communication
In telecommunications, wireless communication may be used to transfer information over short distances (a few meters as in television remote control) or long distances (thousands or millions of kilometers for radio communications). The term is often shortened to "wireless".
Mesh networking (topology) is a type of networking where each node must not only capture and disseminate its own data, but also serve as a relay for other sensor nodes, that is, it must collaborate to propagate the data in the network.
Mesh Network
A mesh network can be designed using a flooding technique or a routing technique. When using a routing technique, the message propagates along a path, by hopping from node to node until the destination is reached. For insuring all its paths' availability, a routing network must allow for continuous connections and reconfiguration around broken or blocked paths, using self-healing algorithms. A mesh network whose nodes are all connected to each other is a fully connected network. Mesh networks can be seen as one type of ad hoc network. Mobile ad hoc networks (MANET) and mesh networks are therefore closely related, but MANET also have to deal with the problems introduced by the mobility of the nodes.
A mobile ad hoc network (MANET), is a self-configuring infra structure lessnetwork of mobile devices connected by wireless links. ad hoc is Latin and means "for this purpose".
Each device in a MANET is free to move independently in any direction, and will therefore change its links to other devices frequently. Each must forward traffic unrelated to its own use, and therefore be a router. The primary challenge in building a MANET is equipping each device to continuously maintain the information required to properly route traffic. Such networks may operate by themselves or may be connected to the larger Internet.
Literature Survey
IEEE 802.11s is a draft IEEE 802.11 amendment for mesh networking, defining how wireless devices can interconnect to create a WLAN mesh network, which may be used for static topologies and ad-hoc networks.
802.11 is a set of IEEE standards that govern wireless networking transmission methods. They are commonly used today in their 802.11a, 802.11b, 802.11g, and 802.11n versions to provide wireless connectivity in the home, office and some commercial establishments.
802.11s inherently depends on one of 802.11a, 802.11b, 802.11g or 802.11ncarrying the actual traffic. One or more routing protocols suitable to the actual network physical topology are required. 802.11s requires (Hybrid Wireless Mesh Protocol, or HWMP),[1] be supported as a default. However, other mesh, ad hoc or dynamically link-state routed (OLSR, B.A.T.M.A.N.) may be supported or even static routing (WDS, OSPF).
A mesh often consists of many small nodes. When mobile users or heavy loads are concerned, there will often be a handoff from one base station to another, and not only from 802.11 but from other (GSM, Bluetooth, PCS and other cordless phone) networks. Accordingly IEEE 802.21, which specifies this handoff between nodes both obeying 802.11s and otherwise, may be required. This is especially likely if a longer-range lower-bandwidth service is deployed to minimize mesh dead zones, e.g. GSM routing based on Open BTS.
Mesh networking often involves network access by previously unknown parties, especially when a transient visitor population is being served. Thus the accompanying IEEE 802.11u standard will be required by most mesh networks to authenticate these users without pre-registration or any prior offline communication.
Wireless Mesh Networking
Mesh Network is a network where all the nodes are connected to each other and is a complete network. In a Mesh Network every node is connected to other nodes on the network through hops. Some are connected through single hops and some may be connected with more than one hope.
The Mesh Network is based on a very sensible concept and has lesser chances of a network breakdown. There are so many possible combinations of routes and hops a data transfer can take that it will reach the destination one way or the other. It is highly unlikely that all the nodes in a single Mesh Network will break down at any given point of time.
Wireless Mesh Networks
Wireless Mesh Networks (WMN) is the networks in which each node can communicate directly with one or more peer nodes.
Different from traditional wireless networks (e.g. 802.11 WLANs) requiring centralized access points to mediate the wireless connection.
Each node operates not only as a host but also as a router, forwarding packets on behalf of other nodes that may not be within direct wireless transmission range of their destinations.
It is dynamically self-organized and self-configured; nodes can automatically establishing and maintaining mesh connectivity among nodes.
Wireless Mesh Networks work based on the radio frequencies and was originally developed by the army to be able to communicate. The reliability factor is high in any kind of Mesh Network. There are three types of wireless Mesh Topologies.
Fixed Mesh Networks
The fixed Mesh Networks will work only in the specified location and they are not mobile networks. They are meant to be used in a limited surrounding with boundaries. The location of nodes in affixed Mesh Network is all pre determined and they are not interchangeable. The fixed Mesh Network does not work on line of sight like the other types of Mesh Networks. The total number of hops in a fixed Mesh Network is usually fixed and also short. There may not be many nodes as these kinds of Mesh Networks exist within an office or building. More often than not the data travels ion a specific direction.
Peer to Peer Mobile Networks
In a peer to peer mobile network the individual devices connect to each other using the Mesh Network. The peer does not require connecting to the main node and they can still communicate from one device to another device by taking the shortest possible data transfer route. However many experts believe that in the peer to peer Mesh Networks the problems with scalability in terms of time taken for data transfer is questionable. The device has to know to transmit the data in the most optimal path and the entire data transfer or depends on this single factor. If the device is incapable then the whole purpose of using it in a peer to peer connection is lost.
Node-To-Node Network
A Node-To-Node network is a combination of fixed Mesh Network and the mobile Mesh Network. In the node to node network a network cloud is introduced and all the nodes are configured to use the network cloud to connect to each other. So this feature makes it mobile and also the network is fixed because all the nodes of the same network connect to one single network cloud.
Network Architecture
The architecture of WMNs can be classified into three types: Infrastructure/Backbone WMNs. In this architecture, mesh routers form an infrastructure for clients, as shown in Fig. 1, where dashed and solid lines indicate wireless and wired links, respectively. The WMN infrastructure/backbone can be built using various types of radio technologies, in addition to the mostly used IEEE 802.11 technologies. The mesh routers form a mesh of self-configuring, self-healing links among themselves. With gateway functionality, mesh routers can be connected to the Internet. This approach, also referred to as infrastructure meshing, provides a backbone for conventional clients and enables integration of WMNs with existing wireless networks, through gateway/bridge functionalities in mesh routers. Conventional clients with an Ethernet interface can be connected to mesh routers via Ethernet links. For conventional clients with the same radio technologies as mesh routers, they can directly communicate with mesh routers. If different radio technologies are used, clients must communicate with their base stations that have Ethernet connections to mesh routers.
Client Meshing
Client meshing provides peer-to-peer networks among client devices. In this type of architecture, client nodes constitute the actual network to perform routing and configuration functionalities as well as providing end-user applications to customers. Hence, a mesh router is not required for these types of networks. Client WMNs are usually formed using one type of radios on devices. Thus, a Client WMN is actually the same as a conventional ad hoc network.
However, the requirements on end-user devices is increased when compared to infrastructure meshing, since in Client WMNs the end-users must perform additional functions such as routing and self-configuration.