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TSMP (Time Synchronised Mesh Protocol) is a networking protocol that forms the foundation of reliable, low-power wireless sensor networking(WSNs). These self-organising, multi-hop networks of wireless sensor nodes are used to monitor and control the physical world. Typical WSN applications include industrial process automation, commercial buildingclimate control, and security alarming.
TSMP provides redundancy and fail-over in time, frequency and space to ensure reliabilityeven in the most challenging radio environments. TSMP also provides the intelligence required for self-organising, self-healing mesh routing. The result is a network that installs with no specialised wireless expertise, automatically adapts to unforeseen challenges, and can be extended as needed without sophisticated planning.
There are five key components of TSMP that contribute to end-to-end network reliability, simple installation, and power efficiency.
Time Synchronised Communication
All node-to-node communication in a TSMP network is transacted in a specific time window. Commonly referred to as Time Division Multiple Access, or TDMA, synchronised communication is a proven technique that provides reliable and efficient transport of wireless data. All nodes share a common sense of time so that they know precisely when to talk, listen, or sleep. This is especially critical in power-constrained applications like WSNs where battery power is often the only option and changing batteries can be costly and cumbersome.
Frequency Hopping
Frequency Hopping Spread Spectrum (FHSS)refers to a method of hopping across multiple frequencies, and is a proven way to sidestep interference and overcome RF challenges. Direct Sequence Spread Spectrum (DSSS) is used with all IEEE 802.15.4 2.4 GHzstandard radios, providing a few dB of coding gain and improvement inmulti-path fading. In the case of TSMP, employing FHSS on top of the802.15.4 radio effectively increases the bandwidth by 16 times. For low data rate applications this means that even if the majority of the band is blocked by RF interference, the messages will still find a clear channel and get through. A frequency hopping TDMA protocol is an efficient means to coordinate node communications.
Automatic Node Joining and Network Formation
TSMP networks are self-organised,every node has the intelligence to discover neighbours, measure RF signal strength, acquire synchronization and frequency hopping information, establish paths and links with neighbours as well as route traffic.During the life of an installation a node joins may join as an end node, becomes a routing node and then reverts back to an end node. Thistype of behaviour is not uncommon in mesh networks and must happen automatically.
Fully-Redundant Mesh Routing
Redundant routing is important in real world RF environments. Conditions may change dramatically over time. A full mesh topology with automatic node joiningand healing lets the network maintain long-term reliability and predictability in spite of these challenges. Fully redundant routing requires both spatial diversity (try a different route) and temporal diversity (try again later). TSMP covers spatial diversity by enabling each node to discover multiple possible parent nodes and then establish links with two or more. Temporal diversity is handled by retry and failover mechanisms.
Secure Message Transfer
There are three pillars of secure message transfer: encryption, authentication and integrity. Encryption keeps the information carried by the message from being read by other parties. Authentication ensures that the sender is actually the sender. Integrity ensures that the message was delivered unaltered. TSMP provides mechanisms for each of these functions.
The Time Synchronised Mesh Protocol (TSMP) was pioneered by Dust Networks, their SmartMesh family of products combines TSMP and standards-based motes to provide proven wireless sensor networking systems. Theproducts are designed to be easily integrated into OEM modules for a wide variety of monitoring and control applications. They achieve highnetwork reliability in the face of unpredictable or harsh RF environments, utilise frequency hopping for interference rejection, and have atypical battery life of 5-10 years. Each node in a SmartMesh-based network is a router, offering mesh-to-the-edge advantage for easy networkintegration, installation and maintenance. With a flexible platform and predictable network performance, OEMs can wirelessly enable a wholehost of solutions for the industrial automation, building automationand defense markets.
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