Most computers are on a network nowadays. Consumer electrical, electronics, and communications products are next. Industrial sensors and controls, machine tools, and other devices in process control and manufacturing are under way. And don't forget about machine-to-machine (M2M), which will let any machine talk to any other machine via several layers of networking.
One day, everything will be networked. That day may be closer than we think thanks to wireless mesh networking. With it, designers can interconnect any device with an inexpensive short-range wireless chip to everything else. This really opens the door to all sorts of new applications that simply weren't possible before.
MESH CONCEPTS In a mesh network, the nodes are all connected to one another. This is called a full mesh (Fig. 1). Each node has a direct link to all other nodes, making for a very useful arrangement. But as the number of nodes increases, the number of links becomes impractical. The number of links (L) is defined by the number of nodes (N) with the expression:
L = N(N - 1)/2
Connecting 20 PCs would require 190 links— a hardware and wiring nightmare. So, practical networks use a bus, ring, star, or other network topology plus some access method to reduce the number of interconnections. The only widely utilized wired mesh network is the Internet.
Going wireless makes the mesh usable and affordable. Furthermore, a partial mesh like the mesh in Figure 2 achieves the primary benefits of the full mesh. Here, not every node is connected to every other node. But if there are enough links, designers can realize some amazing advantages.
Mesh networks are primarily used for monitoring and control operations. As a result, the mesh usually carries sensor readings or control signals. Voice and video typically aren't involved, though some advanced mesh networks make that possible. Because monitor and control operations involve relatively short and simple packets, data rates can be very low. A few kilobits per second is often fast enough, and higher speeds can be implemented if needed. Typical data rates range from 20 to 250 kbits/s.
Perhaps the key benefit of the partial mesh is that the range of each node is greatly multiplied. Most short-range wireless technologies have a typical maximum range of 10 m or less. But this needn't be the maximum communications distance, since all other nodes are used as repeaters or routers.
A signal can be passed from node to node, extending the range indefinitely. In Figure 2, node A can get a message to node L by passing the signal through nodes A-B-E-M-I-L. An alternate path is A-C-D-F-L. There are several other multiple redundant paths, too. The data to be transmitted is put into a packet, and the packet is "hopped" from node to node until it reaches its destination.
In most applications, the nodes attempt to get data to a collection point or access point such as M in Figure 2. The data then is aggregated and sent on to a local-area network (LAN), metro-area network (MAN), or wide-area network (WAN) for further transmission (such as the LAN in a manufacturing plant or the Internet).
A popular variation of the mesh topology is a hybrid consisting of several point-to-multipoint (PMP) star networks, where multiple nodes talk directly to a central coordinating node or access point (AP). Then, the multiple APs are connected in a mesh configuration.
The fact that there's more than one path through a mesh introduces the other major benefit—reliability. If one path fails because of obstructions in the signal path, a defective node, or multipath attenuation, the signal can find one or more alternative routes. If the battery in a node fails, it drops out of the network, but other nodes relay the data via alternative hops.
Movement of people, vehicles, or equipment occasionally may block a previously good wireless path. Furthermore, temporary interference from another source or a sudden noise burst may prevent transmission. Again, a mesh automatically finds another path.
The total number of nodes is an important consideration in a mesh network. To benefit from multiple hop paths, many nodes are required. The absolute minimum mesh configuration is three nodes. Yet adding more nodes will significantly increase the reliability and robustness of the mesh.
Mesh networks also scale well. Initially, they may consist of only a dozen or so nodes. But that can scale to hundreds or even thousands of nodes without difficulties.
In addition, mesh networks are self-forming. The nodes automatically discover one another and establish a link if they're within range. This is called an ad hoc network. If the nodes are mobile, the network constantly and automatically reforms itself to the participating nodes.
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