Mesh networking (topology) is a type of networking where each node must not only capture and disseminate its own data, but also serve as a relay for other nodes, that is, it must collaborate to propagate the data in the network.
A mesh network can be designed using a flooding technique or a routing technique. When using a routing technique, the message is propagated along a path, by hopping from node to node until the destination is reached. To ensure all its paths' availability, a routing network must allow for continuous connections and reconfiguration around broken or blocked paths, using self-healing algorithms. A mesh network whose nodes are all connected to each other is a fully connected network. Mesh networks can be seen as one type of ad hoc network. Mobile ad hoc networks (MANET) and mesh networks are therefore closely related, but MANET also have to deal with the problems introduced by the mobility of the nodes.
The self-healing capability enables a routing based network to operate when one node breaks down or a connection goes bad. 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 is also applicable to wired networks and software interaction.
- Point-to-point line configuration makes identification and isolation of faults easy.
- Messages travel through a dedicated line, directly to the intended recipient; privacy and security are thus enhanced.
- Should a fault occur in a given link, only those communications between that specific pair of devices sharing the link will be affected.
- Dedicated links ensure that each connection carries its own data load, thereby preventing the sort of traffic problems that may arise in shared-link architectures.
- The more extensive the network, in terms of scope or of physical area, the greater the investment necessary to build it will be, due, among other considerations, to the amount of cabling and the number of hardware ports it will require. For this reason, such networks are uncommon.
Wireless mesh networks
Wireless mesh networks were originally developed for military applications. Mesh networks are typically wireless. Over the past decade, the size, cost, and power requirements of radios has declined, enabling multiple radios to be contained within a single device, i.e., mesh node, thus allowing for greater modularity; each can handle multiple frequency bands and support a variety of functions as needed—such as client access, backhaul service, and scanning (required for high-speed handoff in mobile applications)—even customized sets of them.
Zigbee digital radios are incorporated into some consumer appliances, including battery-powered appliances. Zigbee radios spontaneously organize a mesh network, using AODV routing; transmission and reception are synchronized. This means the radios can be off much of the time, and thus conserve power.
In early 2007, the US-based firm Meraki launched a mini wireless mesh router. This is an example of a wireless mesh network (on a claimed speed of up to 50 megabits per second). The 802.11 radio within the Meraki Mini has been optimized for long-distance communication, providing coverage over 250 metres.
This is an example of a single-radio mesh network being used within a community as opposed to multi-radio long range mesh networks like BelAir or MeshDynamics that provide multifunctional infrastructure, typically using tree based topologies and their advantages in O(n) routing.
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.
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.
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.
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 SDR (Software-Defined radio.)
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 are 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 examples is ITU-T G.hn, a standard that specifies a high-speed (up to 1 Gb/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 mesh network. In G.hn, relaying is performed at the Data Link Layer.
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- Babel (protocol)
- Game theory in communication networks
- Mesh node
- Open Garden
- Open Shortest Path First (OSPF)
- Opportunity Driven Multiple Access (ODMA)
- Optical mesh network
- Optimized Link State Routing Protocol (OLSR)
- Shortest Path Bridging
- Spanning Tree Protocol
Mesh network applications
- Wireless mesh network
- Distinct radio node deployments of Wireless Mesh Networking
- Wireless ad hoc network
- Wireless community network
- Mobile ad hoc network (MANET)
- Vehicular ad-hoc network
Mesh network devices
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- Battelle Institute AoA Comparative Ratings for popular mesh network providers, specific to mission critical military programs.
- MIT Roofnet A research project at MIT that forms the basis of roofnet / Meraki mesh networks
- 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
- Phantom anonymous, decentralized network, isolated from the Internet
- Qaul Project Text messaging, file sharing and voice calls independent of internet and cellular networks.