In a traditional network, routers are used to direct data traffic from one place, or node, to another. Each router has a specific set of locations from which it can accept data, and a specific set of locations to which it can send data. A mesh, or multi-hop network, is a highly decentralized way of organizing nodes that does not require predetermined paths between them. Such networks are made possible by mesh routers, which adjust, in real time, the locations with which they can communicate.
Mesh routers work by continuously monitoring network activity and maintaining lists of other devices in their vicinity. When a potential node appears, it broadcasts its address and networking capabilities. Nearby mesh routers will receive the broadcast, and adjust their own lists to reflect the new node. When the device turns off or otherwise disappears, the mesh routers will again update their lists.
If a known device broadcasts a request to send data to a specific location, and a router has the receiving node on its list of active devices, it will complete the path and transmit the data. If no individual mesh router can provide a direct path between transmitting and receiving nodes, the data will be sent to another router in the network, and the process repeated until a path can be found.
Because mesh routers are continuously adjusting to their environment, the network they create is very robust and highly fault tolerant. With a large enough mesh, it is possible to route around any failed or disappeared router; no mesh router can be a point of failure for the entire network. The drawback of such networks is that without predetermined routing paths, data may take a longer time to reach its destination. There are also security issues: because mesh routers automatically talk to every device that appears, it can be easier for malevolent devices to gain access to the network.
Mesh networks are often wireless, and a mesh router can be as simple as a wireless laptop set to operate in ad hoc mode. In this mode, the laptop acts as the router. There are also dedicated devices that provide greater bandwidth and range. Typically, a dedicated mesh router will not be mobile. Many wireless access points are in fact mesh routers, and can be used to create geographically large wireless networks.