Posted by arlene

The wireless mesh network topology for industrial control and sensing that was developed by the MIT Media Lab and produced by the Ember Corporation is a “point-to-point-to-point” or “peer-to-peer” system called an ad hoc, multi-hop network. In a mesh network a node can send and receive messages, but it also functions as a router and can relay messages for its neighbors. Through this relaying process, a packet of wireless data will find its way to its ultimate destination, passing through intermediate nodes with reliable communication links.

1. The resemblance to a map of the Internet is not entirely coincidental. Like the Internet and other router-based communication networks, a mesh network offers multiple redundant communication paths throughout the network.
2. If a single node fails for any reason (including the introduction of strong RF interference), messages will automatically be routed through alternate paths.
3. In a mesh network, the distance between wireless nodes is short, which dramatically increases the link quality between nodes. If you reduce distance by a factor of two, the resulting signal is at least four times more powerful at the receiver. This makes links more reliable without increasing transmitter power in the individual nodes.

The advantages of mesh networks over point-to-point and point-to-multipoint configurations include:

• More Nodes = Greater Reliability: Notice the addition of freestanding “repeater” nodes in the middle of the network, it is possible to extend distance, add redundancy, and improve the general reliability of the network simply by adding repeater nodes.

•  Mesh = Self-Configuring: A network should not need a person to tell it how to get a message to its destination. A mesh network is self-organizing and does not require manual configuration. Because it is both self-configuring and self-healing, adding new gear or relocating existing gear is as simple as plugging in a wireless node and turning it on. The network discovers the new node and automatically incorporates it into the network without the need for a system administrator. A mesh network is not only inherently reliable, it is also highly adaptable. If your tank level sensor and data logger are placed too far apart for a solid RF communication link, you can quickly and easily lay down one or more repeater nodes to fill gaps in the network.

• Mesh = Self-Healing: On the Internet, if one router goes down, messages are sent through an alternate path by other routers. Similarly, if a device in a mesh network fails, messages are sent around it via other devices. The subtraction of one or more nodes does not necessarily affect its operation. A mesh network is self-healing because human intervention is not necessary for rerouting of messages.

• Mesh = Redundant: The actual meaning of “redundancy” in a real world is a matter of degree and must be carefully specified. In a mesh network, the degree of redundancy is essentially a function of nodemesh network can be deliberately overdesigned simply by adding extra nodes, so that each device has two or more paths for sending data. This is a much simpler way of obtaining redundancy density. A than is possible in most other types of systems.

• Mesh = Scalable to Thousands of Nodes: A mesh is also scalable and can handle hundreds or thousands of nodes. Since the operation of the network does not depend upon a central control point, adding multiple data collection points or gateways to other networks is convenient.

It is clear that reliability, adaptability, and scalability are the most important attributes of a wireless network for industrial control and sensing applications. Point-to-point networks can provide reliability, but they do not scale to handle more than one pair of endpoints. Pointto-multipoint networks can handle more endpoints, but the reliability is determined by the placement of the access point and the endpoints.

If environmental conditions result in poor reliability, it is difficult or impossible to adapt a point-to-multipoint network to increase the reliability. By contrast, mesh networks are inherently reliable, adapt easily to environmental or architectural constraints, and can scale to handle thousands of endpoints.

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