Wireless mesh

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Animation showing self healing wireless mesh (enlarge)

A wireless mesh network (WMN) is a communications network made up of radio nodes organized in a mesh topology. The coverage area of the radio nodes working as a single network is sometimes called 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, the rest of the nodes can still communicate with each other, directly or through one or more intermediate nodes. The animation below illustrates how wireless mesh networks can self form and self heal. More animations are available under History of Wireless Mesh Networking

A wireless mesh network can be seen as a type of wireless ad hoc network, where all radio nodes are static and doesn't experience direct mobility.

1 Network Structure
2 Architecture
3 Management
4 Applications
5 Operation
6 Multi-radio mesh
7 Research topics
8 Protocols
- 8.1 Routing protocols
- 8.2 Autoconfiguration protocols
9 See also
10 References
11 External links

Network Structure

Architecture

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, i.e. performs routing. Such an architecture may with careful design provide high bandwidth, spectral efficiency, and economic advantage over the coverage area.

Example of three types of wireless mesh network:

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.

Wireless mesh network have a relatively stable topology except for the occasional failure of nodes or addition of new nodes. The traffic, being aggregated from a large number of end users, changes infrequently. Practically all the traffic in an infrastructure mesh network is either forwarded to or from a gateway, while in ad hoc networks or client mesh networks the traffic flows between arbitrary pairs of nodes.

Management

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 routers to transmit data from nearby nodes to peers that are too far away to reach in a single hop, resulting in a network that can span larger distances. The topology of a mesh network is also more 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 can find another route using a routing protocol.

Applications

Mesh networks may involve either fixed or mobile devices. The solutions are as diverse as communication needs, for example 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. A significant application for wireless mesh networks is VoIP. By using a Quality of Service scheme, the wireless mesh may support local telephone calls to be routed through the mesh.

Operation

The principle is similar to the way packets travel around the wired Internet — data will hop from one device to another until it reaches its destination. Dynamic routing algorithms implemented in each device allow this to happen. To implement such dynamic routing protocols, each device needs to communicate routing information to other devices in the network. Each device then determines what to do with the data it receives — either pass it on to the next device or keep it, depending on the protocol. The routing algorithm used should attempt to always ensure that the data takes the most appropriate (fastest) route to its destination.

Multi-radio mesh

The choice of the 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 within range.

Research topics

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 is 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 being performed for increased efficiency.

Cross-layer design
- Cross-layer research is a popular current research topic where information is shared between different communications layers in order to increase the knowledge and current state of the network. This could enable new and more efficient protocols to be developed.

Protocols

Routing protocols

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

AODV (Ad hoc On-Demand Distance Vector)
OLSR (Optimized Link State Routing protocol)
DSR (Dynamic Source Routing)
OSPF (Open Shortest Path First Routing)
DSDV (Destination-Sequenced Distance-Vector Routing)
B.A.T.M.A.N. (Better Approach To Mobile Adhoc Networking)
PWRP (Predictive Wireless Routing Protocol)
OORP (OrderOne Routing Protocol) (OrderOne Networks Routing Protocol)
TORA (Temporally-Ordered Routing Algorithm)
HSLS (Hazy-Sighted Link State)
IWMP (Infrastructured Wireless Mesh Protocol) for Infrastructred Mesh Networks by UFPB-Brazil

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.

Autoconfiguration protocols

Standard autoconfiguration protocols, such as DHCP or IPv6 stateless autoconfiguration may be used over mesh networks.

Mesh network specific autoconfiguration protocols include:

The Ad-Hoc Configuration Protocol (AHCP)
Proactive Autoconfiguration (Proactive Autoconfiguration Protocol)

References

Iamatechie , "Wifi Mesh Network" Post Series regarding Wifi Mesh Networking

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