Wireless Mesh Network
Main article: History of wireless mesh networking
Wireless mesh architecture is a first step towards providing high-bandwidth network over a specific coverage area. Wireless mesh architecture 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.
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.
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. For example, miner safety has improved with VOIP phones communicating over a mesh network.
Some current applications:
U.S. military forces are now using wireless mesh networking to connect their computers, mainly ruggedized laptops, in field operations. It enables troops to know the locations and status of every soldier or marine, and to coordinate their activities without much direction from central command. Video Clip
Electric meters now being deployed on residences transfer their readings from one to another and eventually to the central office for billing without the need for human meter readers or the need to connect the meters with cables.
The laptops in the one laptop per child program use wireless mesh networking to enable students to exchange files and get on the Internet even though they lack wired or cell phone or other physical connections in their area.
The 66-satellite Iridium constellation operates as a mesh network, with wireless links between adjacent satellites. Calls between two satellite phones are routed through the mesh, from one satellite to another across the constellation, without having to go through an earth station. This makes for a smaller travel distance for the signal, reducing latency, and also allows for the constellation to operate with far fewer earth stations that would be required for 66 traditional communications satellites.
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 refers to a unique pair of dedicated radios on each end of the link. This means there is a unique frequency used for each wireless hop and thus a dedicated CSMA collision domain. This is a true mesh link where you can achieve maximum performance without bandwidth degradation in the mesh and without adding latency. Thus voice and video applications work just as they would on a wired Ethernet network. In true 802.11 networks, there is no concept of a mesh. There are only Access Points (AP’s) and Stations. So a Multi-radio wireless mesh node will dedicate one of the radios to act as a station, and connect to a neighbor node AP radio. Single and dual-radio mesh use proprietary means to repeat the signal which means that more than two nodes are in the same collision domain and frequency.Animation. That is what causes bandwidth degradation and high latency. Detailed explanation Here.
One of the most often cited papers on Wireless Mesh Networks identified the following areas as open research problems in 2005 :
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 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. It is important to note that careless cross-layer design could lead to code which is difficult to maintain and extend.
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 (Infrastructure Wireless Mesh Protocol) for Infrastructure Mesh Networks by GRECO 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.
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)
Dynamic WMN Configuration Protocol (DWCP)
Wikimedia Commons has media related to: Mesh network
Mobile ad-hoc network
Wireless ad-hoc network
Wireless Distribution System
Peer to peer
Ant colony optimization
Wireless community network
Optimized Link State Routing protocol
Public Safety Network
comparison of wireless data standards
^ a b c 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
^ J. Jun, M.L. Sichitiu, “The nominal capacity of wireless mesh networks”, in IEEE Wireless Communications, vol 10, 5 pp 8-14. October 2003
^ S.M. Chen, P, Lin, D-W Huang, S-R Yang, “A study on distributed/centralized scheduling for wireless mesh network” in Proceedings of the 2006 International Conference on Wireless Communications and Mobile Computing, pp 599 – 604. Vancouver, British Columbia, Canada. 2006
^ V. Kawadia, P.R. Kumar, “A Cautionary Perspective on Cross-Layer Design,” in IEEE Wireless Communications, pp 3-11, February 2005.
How Wireless Mesh Networks Work at HowStuffWorks
IET From hotspots to blankets
Mesh Network serves three California Communities
Using Mesh Networks for Video Surveillance
LastMile Wireless Mesh Networks An Industry Overview
Ian. F. Akyildiz and Xudong Wang, “A Survey on Wireless Mesh Networks,” IEEE Communications Magazine, vol. 43, no. 9, s23-s30, Sept. 2005
Iamatechie , “Wifi Mesh Network” Post Series regarding Wifi Mesh Networking
Mesh Networks Research Group Projects and tutorials’ compilation related to the Wireless Mesh Networks
Victor Pierobon, “The first concept of wireless mesh” The 1994 beginning of wireless mesh.
Building a Rural Wireless Mesh Network Guide
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