ArchitecturesA well-designed WSN solution will employ techniques to both increase transmission reliability and quickly adapt should the transmission fail. Techniques such as frequency-hopping and direct sequence spreading can be used by the radio to increase the chance that any single transmission gets through. This is mature and well proven technology. The innovation of WSNs is the ability to automatically route around failed links. This requires embedded networking intelligence that establishes, maintains and utilizes redundant multi-hop routing from source to destination. And, rather than force installers to foresee every possible interferer and obstacle, the WSN should be able to self-organize and self-heal in real time to make best use of available radio links. Systems that require complex site surveys or path-by-path configuration are not economically feasible.As the WSN market has evolved, several different architectures have emerged – all with very different attributes. The three broad categories are star, star-mesh and full-mesh. Star-Mesh: Star-mesh networks have redundant routing at the core and star routing at the edge – typically with line-powered routing nodes and optionally battery-powered end nodes. ZigBee networks are star-mesh and refer to routing nodes as ‘full-function devices’ and the end nodes as ‘reduced-function devices’. While star-mesh does provide redundancy on top of star topologies they do not allow for true end-to-end redundancy nor do they eliminate the installation challenges of star networks. While an edge node may transmit to one of many routers it is still a point-to-point link that must be tuned. Mesh: Full-mesh networks, sometimes referred to as ‘mesh-to-the-edge’, provide fully redundant routing to the edge of the network. This has the obvious benefit of reliability but also has dramatic impact on network installation and long-term predictability. In a full-mesh network every device has the same routing capabilities. As it is installed each node will be able to ‘decide’ where it belongs in the routing structure based on what other nodes it can communicate with, its proximity to the network gateway, and its traffic load. This allows for true self-forming and self-healing without constraints imposed by device type and architecture. Dust Networks SmartMesh family of embedded wireless products are based on full mesh networking technology and utilize TSMP (Time Synchronized Mesh Protocol) to deliver unprecedented reliability, ultra low-power and ease of installation. |
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