A mesh network (or simply meshnet) is a local network topology in which the infrastructure nodes (i.e. bridges, switches and other infrastructure devices) connect directly, dynamically and non-hierarchically to as many other nodes as possible and cooperate with one another to efficiently route data from/to clients. This lack of dependency on one node allows for every node to participate in the relay of information. Mesh networks dynamically self-organize and self-configure, which can reduce installation overhead. The ability to self-configure enables dynamic distribution of workloads, particularly in the event that a few nodes should fail. This in turn contributes to fault-tolerance and reduced maintenance costs.
Mesh topology may be contrasted with conventional star/tree local network topologies in which the bridges/switches are directly linked to only a small subset of other bridges/switches, and the links between these infrastructure neighbours are hierarchical. While star-and-tree topologies are very well established, highly standardized and vendor-neutral, vendors of mesh network devices have not yet all agreed on common standards, and interoperability between devices from different vendors is not yet assured.
Mesh networks can relay messages using either a flooding technique or a routing technique. With routing, the message is propagated along a path by hopping from node to node until it reaches its destination. To ensure that all its paths are available, the network must allow for continuous connections and must reconfigure itself around broken paths, using self-healing algorithms such as Shortest Path Bridging. Self-healing allows a routing-based network to operate when a node breaks down or when a connection becomes unreliable. As a result, the network is typically quite reliable, as there is often more than one path between a source and a destination in the network. Although mostly used in wireless situations, this concept can also apply to wired networks and to software interaction.
A mesh network whose nodes are all connected to each other is a fully connected network. Fully connected wired networks have the advantages of security and reliability: problems in a cable affect only the two nodes attached to it. However, in such networks, the number of cables, and therefore the cost, goes up rapidly as the number of nodes increases.
Wireless mesh radio networks were originally developed for military applications, such that every node could dynamically serve as a router for every other node. In that way, even in the event of a failure of some nodes, the remaining nodes could continue to communicate with each other, and, if necessary, to serve as uplinks for the other nodes.
Early wireless mesh network nodes had a single half-duplex radio that, at any one instant, could either transmit or receive, but not both at the same time. This was accompanied by the development of shared mesh networks. This was subsequently superseded by more complex radio hardware that could receive packets from an upstream node and transmit packets to a downstream node simultaneously (on a different frequency or a different CDMA channel). This allowed the development of switched mesh networks. As the size, cost, and power requirements of radios declined further, nodes could be cost-effectively equipped with multiple radios. This in turn permitted each radio to handle a different function, for instance one radio for client access, and another for backhaul services.
- Packet radio networks or ALOHA networks were first used in Hawaii to connect the islands. Given the bulk radios, and low data rate, the network is less useful than it was envisioned to be.
- In 1998-1999, a field implementation of a campus wide wireless network using 802.11 WaveLAN 2.4 GHz wireless interface on several laptops was successfully completed. Several real applications, mobility and data transmissions were made.
- Mesh networks were useful for the military market because of the radio capability, and because not all military missions have frequently moving nodes. The Pentagon launched the DoD JTRS program in 1997, with an ambition to use software to control radio functions - such as frequency, bandwidth, modulation and security previously baked into the hardware. This approach would allow the DoD to build a family of radios with a common software core, capable of handling functions that were previously split among separate hardware-based radios: VHF voice radios for infantry units; UHF voice radios for air-to-air and ground-to-air communications; long-range HF radios for ships and ground troops; and a wideband radio capable of transmitting data at megabit speeds across a battlefield. However, JTRS program was shut down in 2012 by the US Army because the radios made by Boeing had a 75% failure rate.
- Google Home, Google Wi-Fi, and Google OnHub all support Wi-Fi mesh networking.
- In rural Catalonia, Guifi.net was developed in 2004 as a response to the lack of broadband Internet, where commercial Internet providers weren't providing a connection or a very poor one. Nowadays with more than 30,000 nodes it is only halfway a fully connected network, but following a peer to peer agreement it remained an open, free and neutral network with extensive redundancy.
- In 2004, TRW Inc. engineers from Carson, California, successfully tested a multi-node mesh wireless network using 802.11a/b/g radios on several high speed laptops running Linux, with new features such as route precedence and preemption capability, adding different priorities to traffic service class during packet scheduling and routing, and quality of service. Their work concluded that data rate can be greatly enhanced using MIMO technology at the radio front end to provide multiple spatial paths.
- ZigBee digital radios are incorporated into some consumer appliances, including battery-powered appliances. ZigBee radios spontaneously organize a mesh network, using specific routing algorithms; transmission and reception are synchronized. This means the radios can be off much of the time, and thus conserve power. ZigBee is for low power low bandwidth application scenarios.
- Thread is a consumer wireless networking protocol built on open standards and IPv6/6LoWPAN protocols. Thread's features include a secure and reliable mesh network with no single point of failure, simple connectivity and low power. Thread networks are easy to set up and secure to use with banking-class encryption to close security holes that exist in other wireless protocols. In 2014 Google Inc's Nest Labs announced a working group with the companies Samsung, ARM Holdings, Freescale, Silicon Labs, Big Ass Fans and the lock company Yale to promote Thread.
- In early 2007, the US-based firm Meraki launched a mini wireless mesh router. The 802.11 radio within the Meraki Mini has been optimized for long-distance communication, providing coverage over 250 metres. In contrast to multi-radio long range mesh networks with tree based topologies and their advantages in O(n) routing, the Maraki had only one radio, which it used for both client access as well as backhaul traffic.
- The Naval Postgraduate School, Monterey CA, demonstrated such wireless mesh networks for border security. In a pilot system, aerial cameras kept aloft by balloons relayed real time high resolution video to ground personnel via a mesh network.
- SPAWAR, a division of the US Navy, is prototyping and testing a scalable, secure Disruption Tolerant Mesh Network  to protect strategic military assets, both stationary and mobile. Machine control applications, running on the mesh nodes, "take over", when Internet connectivity is lost. Use cases include Internet of Things e.g. smart drone swarms.
- An MIT Media Lab project has developed the XO-1 laptop or "OLPC" (One Laptop per Child) which is intended for disadvantaged schools in developing nations and uses mesh networking (based on the IEEE 802.11s standard) to create a robust and inexpensive infrastructure. The instantaneous connections made by the laptops are claimed by the project to reduce the need for an external infrastructure such as the Internet to reach all areas, because a connected node could share the connection with nodes nearby. A similar concept has also been implemented by Greenpacket with its application called SONbuddy.
- In Cambridge, UK, on 3 June 2006, mesh networking was used at the “Strawberry Fair” to run mobile live television, radio and Internet services to an estimated 80,000 people.
- Broadband-Hamnet , a mesh networking project used in amateur radio, is "a high-speed, self-discovering, self-configuring, fault-tolerant, wireless computer network" with very low power consumption and a focus on emergency communication.
- The Champaign-Urbana Community Wireless Network (CUWiN) project is developing mesh networking software based on open source implementations of the Hazy-Sighted Link State Routing Protocol and Expected Transmission Count metric. Additionally, the Wireless Networking Group in the University of Illinois at Urbana-Champaign are developing a multichannel, multi-radio wireless mesh testbed, called Net-X as a proof of concept implementation of some of the multichannel protocols being developed in that group. The implementations are based on an architecture that allows some of the radios to switch channels to maintain network connectivity, and includes protocols for channel allocation and routing.
- FabFi is an open-source, city-scale, wireless mesh networking system originally developed in 2009 in Jalalabad, Afghanistan to provide high-speed Internet to parts of the city and designed for high performance across multiple hops. It is an inexpensive framework for sharing wireless Internet from a central provider across a town or city. A second larger implementation followed a year later near Nairobi, Kenya with a freemium pay model to support network growth. Both projects were undertaken by the Fablab users of the respective cities.
- SMesh is an 802.11 multi-hop wireless mesh network developed by the Distributed System and Networks Lab at Johns Hopkins University. A fast handoff scheme allows mobile clients to roam in the network without interruption in connectivity, a feature suitable for real-time applications, such as VoIP.
- Many mesh networks operate across multiple radio bands. For example, Firetide and Wave Relay mesh networks have the option to communicate node to node on 5.2 GHz or 5.8 GHz, but communicate node to client on 2.4 GHz (802.11). This is accomplished using software-defined radio (SDR).
- The SolarMESH project examined the potential of powering 802.11-based mesh networks using solar power and rechargeable batteries. Legacy 802.11 access points were found to be inadequate due to the requirement that they be continuously powered. The IEEE 802.11s standardization efforts are considering power save options, but solar-powered applications might involve single radio nodes where relay-link power saving will be inapplicable.
- The WING project (sponsored by the Italian Ministry of University and Research and led by CREATE-NET and Technion) developed a set of novel algorithms and protocols for enabling wireless mesh networks as the standard access architecture for next generation Internet. Particular focus has been given to interference and traffic aware channel assignment, multi-radio/multi-interface support, and opportunistic scheduling and traffic aggregation in highly volatile environments.
- WiBACK Wireless Backhaul Technology has been developed by the Fraunhofer Institute for Open Communication Systems (FOKUS) in Berlin. Powered by solar cells and designed to support all existing wireless technologies, networks are due to be rolled out to several countries in sub-Saharan Africa in summer 2012.
- Recent standards for wired communications have also incorporated concepts from Mesh Networking. An example is ITU-T G.hn, a standard that specifies a high-speed (up to 1 Gbit/s) local area network using existing home wiring (power lines, phone lines and coaxial cables). In noisy environments such as power lines (where signals can be heavily attenuated and corrupted by noise) it's common that mutual visibility between devices in a network is not complete. In those situations, one of the nodes has to act as a relay and forward messages between those nodes that cannot communicate directly, effectively creating a "relaying" network. In G.hn, relaying is performed at the Data Link Layer.
- Category of mesh networking technologies
- Bluetooth mesh networking
- Wireless mesh network
- Optical mesh network
- Wireless network
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- Battelle Institute AoA Comparative Ratings for popular mesh network providers, specific to mission critical military programs.
- Architecture and Evaluation of the MIT Roofnet Mesh Network - Draft research paper describing the Roofnet project.
- WING Project Wireless Mesh Network distribution based on the roofnet source code
- First, Second and Third Generation Mesh Architectures History and evolution of Mesh Networking Architectures
- DARPA's ITMANET program and the FLoWS Project Investigating Fundamental Performance Limits of MANETS
- Robin Chase discusses Zipcar and Mesh networking Robin Chase talks at the Ted conference about the future of mesh networking and eco-technology
- Dynamic And Persistent Mesh Networks Hybrid mesh networks for military, homeland security and public safety
- Mesh Networks Research Group Projects and tutorials' compilation related to the Wireless Mesh Networks
- Tetrahedron Core Network Application of a tetrahedral structure to create a resilient partial-mesh 3-dimensional campus backbone data network
- Phantom anonymous, decentralized network, isolated from the Internet
- Qaul Project – Text messaging, file sharing and voice calls independent of Internet and cellular networks
- the free content wiki for project meshnet and supporting projects
- Broadband-Hamnet - Mesh networking application on 2.4Ghz spectrum for amateur radio
- AREDN - Amateur Radio Emergency Data network, a mesh networking application used for emergency data and information handling
- Disruption Tolerant Mesh Networks autonomous machine controller in mesh nodes operate despite loss of cloud connectivity.
- Hyperboria Peer-to-peer IPv6 network with automatic end-to-end encryption