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A wireless mesh network is a communications network made up of radio nodes in which there are at least two pathways of communication to each node. The coverage area of the radio nodes working as a single network becomes a mesh cloud. Access to this mesh cloud is dependent on the radio nodes working in harmony with each other to create a radio network. A mesh network is reliable and offers redundancy. When one node can no longer operate, all the rest can still communicate with each other, directly or through one or more intermediate nodes. The diagrams below illustrate how wireless mesh networks can self form and self heal.

Wireless mesh builds routes between nodes only as desired by originating nodes. It maintains these routes as long as they are needed by the originating node. Wireless mesh nodes forms paths in term of hops which connect together to form the wireless mesh network. Hops are the number of nodes between two a receiving and transmitting client i.e. Laptop, PC, Wi-Fi telephone, IP appliance, etc. Symbolically a Wireless Mesh network is represented by a network cloud.

Mesh nodes uses sequence numbers to ensure the freshness of routes (please note that various protocols may differ.) It is loop-free, self-starting, and scales to large numbers of nodes. Wireless Mesh Nodes builds routes using a route request, route reply query cycle. When a node desires a route to a destination for which it does not already have a route, it broadcasts a route request packet across the network. Nodes receiving this packet update their information for the source node and set up backwards pointers to the source node in the route tables. The wireless nodes also collect other active modes including IP address, current sequence number, and broadcast ID, and contains the most recent sequence number for the destination of which the source node is aware. A node receiving a route request may send a route reply when it is either the destination or if it has a route to the destination with corresponding sequence number greater than or equal to that contained in the route request. Nodes keep track of the route request through source IP address and broadcast ID. The nodes know when they receive a route request which they have already processed; they discard it and will not forward it.

As the backward pointers propagates back to the originating node, it then sets up forward pointers to the destination. Once the source node receives the backward pointers, it may begin to forward data packets to the destination. When the source later receives a backwards pointer containing a greater sequence number or contains the same sequence number with a smaller hop count, it may update its routing information for that destination and begin using the better route.

As long as the route remains active, it will continue to be maintained. A route is considered active as long as there are data packets periodically travelling from the source to the destination along that path. Once the source stops sending data packets, the links will time out and eventually be deleted from the intermediate node routing tables. Most wireless mesh nodes maintain routes for as long as the route is active. This includes maintaining hops for the life of the cloud. Because the network nodes can be mobile or shut down, it is likely that many link breakages along a route will occur during the lifetime of that route.

Contents 1 History 2 Network Structure 2.1 Architecture 2.2 Management 2.3 Applications 2.4 Operation 2.5 Multi-radio mesh 2.6 Radio Techniques 3 Protocols 4 See also 5 References 6 External links

Main article: History of wireless mesh networking

Wireless mesh networking has seen three distinct configuration of technology, each incorporating iterative improvements allowing for greater range, reliability, and cost efficiency.

Some early-configuration of mesh networking products performed poorly in the substantially "multi-hop" (involving many node-to-node connections) environments in which they were deployed. However, more recent History_of_wireless_mesh_networking have seen improvements to this situation.

All wireless mesh networking that is pre IEEE standard is known as First Generation Wireless Mesh Network.

Wireless mesh architecture is a first step towards providing high-bandwidth network over a specific coverage area. Wireless mesh architecture’s infrastructure is, in effect, a router network minus the cabling between nodes. It's built of peer radio devices that don't have to be cabled to a wired port like traditional WLAN access points (AP) do. Mesh architecture sustains signal strength by breaking long distances into a series of shorter hops. Intermediate nodes not only boost the signal, but cooperatively make forwarding decisions based on their knowledge of the network. Such architecture provides high bandwidth, spectral efficiency, and economic advantage over the coverage area.

Wireless mesh network have a relatively stable topologyexcept for occasional nodes failure or addition. The traffic, being aggregated from a large number of end users, changes infrequently. Practically all the traffic is either forwarded to or from a gateway, while in ad hoc networks the traffic flows between arbitrary pairs of nodes. A multi hop based nodes proactive routing scheme is used for traffic forwarding, since it easily allow flows aggregation and would minimize overhead, ensuring an optimal utilization of bandwidth.

Three types of infrastructure have been identified:

• Infrastructure wireless mesh networks: Mesh routers form an infrastructure for clients.
• Client wireless mesh networks: Client nodes constitute the actual network to perform routing and configuration functionalities
• Hybrid wireless mesh networks: Mesh clients can perform mesh functions with other mesh clients as well as accessing the network through mesh routers.

This type of infrastructure can be decentralized (with no central server) or centrally managed (with a central server), both are relatively inexpensive, and very reliable and resilient, as each node needs only transmit as far as the next node. Nodes act as repeaters to transmit data from nearby nodes to peers that are too far away to reach, resulting in a network that can span large distances, especially over rough or difficult terrain. Mesh networks are also extremely reliable, as each node is connected to several other nodes. If one node drops out of the network, due to hardware failure or any other reason, its neighbors simply find another route. Extra capacity can be installed by simply adding more nodes.

Mesh networks may involve either fixed or mobile devices. The solutions are as diverse as communications in difficult environments such as emergency situations, tunnels and oil rigs to battlefield surveillance and high speed mobile video applications on board public transport or real time racing car telemetry. The most significant application for wireless mesh is VoIP. Using Quality of Service in wireless mesh telephone calls can be routed through the mesh.

The principle is similar to the way packets travel around the wired Internet — data will hop from one device to another until it reaches a given destination. Dynamic routing capabilities included in each device allow this to happen. To implement such dynamic routing capabilities, each device needs to communicate its routing information to every device it connects with, "almost in real time". Each device then determines what to do with the data it receives — either pass it on to the next device or keep it. The routing algorithm used should attempt to always ensure that the data takes the most appropriate (fastest) route to its destination.

The choice of radio technology for wireless mesh networks is crucial. In a traditional wireless network where laptops connect to a single access point, each laptop has to share a fixed pool of bandwidth. With mesh technology and adaptive radio, devices in a mesh network will only connect with other devices that are in a set range. The advantage is that, like a natural load balancing system, the more devices the more bandwidth becomes available, provided that the number of hops in the average communications path is kept low.

• New modulation scheme
  • In order to achieve higher transmission rate, new wideband transmission schemes other than OFDM and UWB are needed.

• Advanced antenna processing
  • Advanced antenna processing including directional, smart and multiple antenna technologies must be further investigated, since their complexity and cost are still too high for wide commercialization.

• Flexible spectrum management
  • Tremendous efforts on research of frequency-agile techniques are required for their practical use.

• media access control
  • Cross-layer research also should be further investigated, so as to best utilize the advanced features provided by the physical layer.

There are more than 70 competing schemes for routing packets across mesh networks. Some of these include:

• DSDV (Destination-Sequenced Distance-Vector Routing)
• AODV (Ad-hoc On Demand Distance Vector)
• B.A.T.M.A.N. (Better Approach To Mobile Adhoc Networking)
• PWRP (Predictive Wireless Routing Protocol)
• DSR (Dynamic Source Routing)
• OLSR (Optimized Link State Routing protocol)
• OORP (OrderOne Routing Protocol) (OrderOne Networks Routing Protocol)
• TORA (Temporally-Ordered Routing Algorithm)
• HSLS (Hazy-Sighted Link State)

The IEEE is developing a set of standards under the title 802.11s to define an architecture and protocol for ESS Mesh Networking.

A more thorough list can be found at Ad hoc routing protocol list.

• Ian F. Akyildiz , Xudong Wang , Weilin Wang, "Wireless mesh networks: a survey", Computer Networks and ISDN Systems, v.47 n.4,p.445-487, 15 March 2005

• Ian. F. Akyildiz and Xudong Wang, "A Survey on Wireless Mesh Networks," IEEE Communications Magazine, vol. 43, no. 9, s23-s30, Sept. 2005

• DARPA's ITMANET program and the FLoWS Project Investigating Fundamental Performance Limits of MANETS
• Analysis of Mesh Architectures Why all mesh products are not created equal.
• Wireless Mesh Networks Advantages and applications for Industrial and Mobile Solutions]
• What is Third Generation Mesh? Review of three generation of mesh networking architectures.
• Wifi Mesh Networking Softwares My Experiments with Wifi Mesh Networks.
• Wayflex First mesh based ISP in Brazil.
• Roofnet.net Mesh network documentation and monitoring for MIT-based roofnet networks
• Is Multi-radio mesh worthwhile? Cost considerations of multi-radio mesh.
• Moskaluk Wireless Mesh Don Moskaluk Mesh network documentation and monitoring for Locustworlds Open Source AODV
• NetEquality A non-profit building mesh networks for low-income neighborhoods
• IET From hotspots to blankets
• Remesh Brazilian Mesh Project
• Infinet Wireless (WiMAX, MESH Equipment)
• Wireless Mesh Mine Communications (Wireless Mesh Communication System)
• Robust Wireless Mesh Communications inside mines - successful pilots
• HauteSpot Networks (Wireless Video Surveillance, HD Electronic News Gathering, Sensor Networks, MESH, and 802.11 Equipment) Solutions for public safety, broadcast, surveillance, law enforcement and SCADA