Wireless mesh network
A mesh refers to rich interconnection among devices or nodes. Wireless mesh networks often consist of mesh clients, mesh routers and gateways. Mobility of nodes is less frequent. If nodes constantly or frequently move, the mesh spends more time updating routes than delivering data. In a wireless mesh network, topology tends to be more static, so that routes computation can converge and delivery of data to their destinations can occur. Hence, this is a low-mobility centralized form of wireless ad hoc network. Also, because it sometimes relies on static nodes to act as gateways, it is not a truly all-wireless ad hoc network.
Mesh clients are often laptops, cell phones, and other wireless devices. Mesh routers forward traffic to and from the gateways, which may, but need not, be connected to the Internet. The coverage area of all radio nodes working as a single network is sometimes called a mesh cloud. Access to this mesh cloud depends on the radio nodes working together 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. Wireless mesh networks can self form and self heal. Wireless mesh networks work with different wireless technologies including 802.11, 802.15, 802.16, cellular technologies and need not be restricted to any one technology or protocol. See also mesh networking.
Wireless mesh architecture is a first step towards providing cost effective and low mobility over a specific coverage area. Wireless mesh infrastructure is, in effect, a network of routers minus the cabling between nodes. It is built of peer radio devices that do not have to be cabled to a wired port like traditional WLAN access points (AP) do. Mesh infrastructure carries data over large distances by splitting the distance into a series of short hops. Intermediate nodes not only boost the signal, but cooperatively pass data from point A to point B by making forwarding decisions based on their knowledge of the network, i.e. perform routing by first deriving the topology of the network.
Wireless mesh networks is a relatively "stable-topology" network except for the occasional failure of nodes or addition of new nodes. The path of 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 wireless ad hoc networks or client mesh networks the traffic flows between arbitrary pairs of nodes.
If rate of mobility among nodes are high, i.e., link breaks happen frequently, wireless mesh networks start to break down and have low communication performance.
This type of infrastructure can be decentralized (with no central server) or centrally managed (with a central server). Both are relatively inexpensive, and can be 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 must be relatively stable, i.e., not too much mobility. If one node drops out of the network, due to hardware failure or any other reason, its neighbors can quickly 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, oil rigs, battlefield surveillance, high-speed mobile-video applications on board public transport, real-time racing-car telemetry, or self-organizing Internet access for communities. An important possible application for wireless mesh networks is VoIP. By using a quality of service scheme, the wireless mesh may support routing local telephone calls through the mesh. Most applications in wireless mesh networks are similar to those in wireless ad hoc networks.
Some current applications:
- U.S. military forces are now using wireless mesh networking to connect their computers, mainly ruggedized laptops, in field operations.
- Electric smart 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.
- Google Home, Google Wi-Fi, and Google OnHub all support Wi-Fi mesh (i.e., Wi-Fi ad hoc) networking. Several manufacturers of Wi-Fi routers began offering mesh routers for home use in the mid-2010s.
- 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 than would be required for 66 traditional communications satellites.
The principle is similar to the way packets travel around the wired Internet—data hops from one device to another until it eventually 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 having different radios operating at different frequencies to interconnect nodes in a mesh. This means there is a unique frequency used for each wireless hop and thus a dedicated CSMA collision domain. With more radio bands, communication throughput is likely to increase as a result of more available communication channels. This is similar to providing dual or multiple radio paths to transmit and receive data.
One of the more often cited papers on Wireless Mesh Networks identified the following areas as open research problems in 2005
- New modulation scheme
- Advanced antenna processing
- Flexible spectrum management
- Tremendous efforts on research of frequency-agile techniques are being performed for increased efficiency.
- Cross-layer optimization
- Cross-layer research is a popular current research topic where information is shared between different communications layers to increase the knowledge and current state of the network. This could facilitate development of new and more efficient protocols. A joint protocol that addresses various design problems—routing, scheduling, channel assignment etc.—can achieve higher performance since these problems are strongly co-related. Note that careless cross-layer design can lead to code that is difficult to maintain and extend.
- Software-defined wireless networking
- Centralized, distributed, or hybrid? - In  a new SDN architecture for WDNs is explored that eliminates the need for multi-hop flooding of route information and therefore enables WDNs to easily expand. The key idea is to split network control and data forwarding by using two separate frequency bands. The forwarding nodes and the SDN controller exchange link-state information and other network control signaling in one of the bands, while actual data forwarding takes place in the other band.
- A WMN can be seen as a group of nodes (clients or routers) that cooperate to provide connectivity. Such an open architecture, where clients serve as routers to forward data packets, is exposed to many types of attacks that can interrupt the whole network and cause denial of service (DoS) or Distributed Denial of Service (DDoS).
There are more than 70 competing schemes for routing packets across mesh networks. Some of these include:
- Associativity-Based Routing (ABR)
- AODV (Ad hoc On-Demand Distance Vector)
- B.A.T.M.A.N. (Better Approach To Mobile Adhoc Networking)
- Babel (protocol) (a distance-vector routing protocol for IPv6 and IPv4 with fast convergence properties)
- Dynamic NIx-Vector Routing|DNVR
- DSDV (Destination-Sequenced Distance-Vector Routing)
- DSR (Dynamic Source Routing)
- HSLS (Hazy-Sighted Link State)
- HWMP (Hybrid Wireless Mesh Protocol, the default mandatory routing protocol of IEEE 802.11s)
- Infrastructure Wireless Mesh Protocol (IWMP) for Infrastructure Mesh Networks by GRECO UFPB-Brazil
- OLSR (Optimized Link State Routing protocol)
- OORP (OrderOne Routing Protocol) (OrderOne Networks Routing Protocol)
- OSPF (Open Shortest Path First Routing)
- Routing Protocol for Low-Power and Lossy Networks (IETF ROLL RPL protocol, RFC 6550)
- PWRP (Predictive Wireless Routing Protocol)
- TORA (Temporally-Ordered Routing Algorithm)
- ZRP (Zone Routing Protocol)
A less thorough list can be found at Ad hoc routing protocol list.
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Mesh network specific autoconfiguration protocols include:
- Ad Hoc Configuration Protocol (AHCP)
- Proactive Autoconfiguration (Proactive Autoconfiguration Protocol)
- Dynamic WMN Configuration Protocol (DWCP)
Communities and providersEdit
- Aruba AirMesh- multiservice wireless mesh networks for outdoors 
- Ruckus Mesh - Smart Mesh
- Cisco Meraki - Mesh networking - access points as gateways and repeaters
- Juniper Wireless Mesh - Wireless mesh and bridging
- TP-Link - Wireless mesh networking - access points 
- Others - list of venture backed mesh networking companies.
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- Mesh Networks Research Group Projects and tutorials' compilation related to the Wireless Mesh Networks
- Linux Wireless Subsystem (80211) by Rami Rosen
- IWT Wireless Communications and Tracking in Underground Mines