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LON Technology Overview
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  1. LON Technology Overview Lecture 11

  2. Targets of Lecture • Basics of LON technology • LONTalk protocol • Addressing, channels, routers, SNVTs • Designing LON networks • Topologies, channel types, cabling

  3. Basic data about LON • Local Operating Network ~ field bus ~ control network • Echelon Corporation, US, has developed LonWorks technology • The technology provides • Components for building the networks • Tools for installation, maintenance and network development • Over 3500 companies are currently using the technology • Control network ~ data transfer network for short control messages (12 bytes) • LON network utilizes LonTalk protocol (CSMA) • Protocol is installed in all LON nodes

  4. 1 1 0 1 1 0 1 1 Network Oscillator Transceiver Neuron 3150 circuit Power supply I/O connections I/O device Memory Operating system I/O & function library User application Protocol Lon node

  5. Benefits of LON • Reduced amount of cabling, easier to make changes • Products of different manufacturers fit in the same solution • Devices of different systems communicate in the same network => better solutions as a whole • Getting rid of separate networks • Different systems can utilize same field devices • Different systems can utilize same external data connections • Open solution is under continuous development - the investment can be utilized also in the future

  6. LonTalk protocol

  7. LonTalk protocol • Defines the rules for communication in the network • Protocols are divided into layers, which provide different services • Ready in all LON nodes • Based on CSMA technology (Carrier Sense Multiple Access) • Independent of data transmission media • Suitable for transferring short control messages (~12 bytes/ message)

  8. I/O I/O Nodes Channels: All nodes attached to the channel hear all packages Router: Routes packages selectively between channels Message header Recipient’s address Sender’s address Message type Message contents Error check End of message LonTalk: Contents of packages

  9. LonTalk: Channels • Each node is attached to one channel • All nodes attached to the channel hear all channel traffic • Nodes share the transmission capacity of the channel, i.e. the bandwidth • Different channels of the LON network are connected to each other with routers • 4 different routing algorithms: repeater, bridge, configured router and learning router

  10. LonTalk: Addressing • Every node has (at least) one unique network address • Address structure is hierarchical (3 levels) • Highest hierarchy level domain address • system level address • nodes in the same channel can be divided into different main networks • domain address can be 0, 1, 3 or 6 bytes long • Domain is divided at most 255 subnets, with no more than 127 nodes in each • 255 subnets / domain * 127 nodes / subnet = 32 385 nodes / domain • Nodes can also have group addresses • Max 256 groups / domain

  11. LonTalk: Ways of addressing • Domain, Subnet= 0 • For all nodes in the domain • Domain, Subnet • For all nodes in the subnet • Domain, Subnet, Node • For a specific single node • Domain, Group • For all nodes in a group • Neuron ID • For a specific physical Neuron circuit • Used when installing the node

  12. Repeater, bridge and router • Repeater • Repeats all packages as such and transmits them to another segment • Used for increasing the number of nodes and amount of cabling • Bridge • Passes all packages coming from the same domain • Used for combining channels using open media • Router • Passes only the packages that are going to another channel • Used for combining channels of different kind, for increasing the number of nodes and amount of cabling, and for limiting the amount of traffic

  13. Segment 1 Segment 2 Channel A Subnet A Subnet B Repeater Router Segment 3 Channel B Subnet C Subnet D LonTalk: Channel and segment • One segment can include several subnets • Subnets cannot continue over a ”smart” router • Channels are connected through smart routers • Bandwidth of a channel is shared by all of its nodes

  14. Authenticated message Receiving node - Generates a random number, uses common key for comparing the answer to the reply received from the sender Sending node - Common key for changing the challenge with the authentication algorithm 64-bit random number Calculated reply Acknowledgement LonTalk: Authentication • Confirms the identity of the sender • Uses a 48-bit secret key, which is known by all nodes in the domain • The sender has to return right reply to the 64-bit challenge

  15. Standard network variables, SNVT • Through ‘snivits’, different quantities and data can be expressed unambiguously • Three types of network variables: • coming from LON network to the node= nvi (network variable input) • going from node to LON network = nvo (network variable output) • configuration parameters, i.e. definition parameters = nci (network configuration input) • 201 standard network variables are defined in the SNVT list v.13.04

  16. You can forget most of the LonTalk protocol • Installation tools automate and hide the details of the protocol • The installer of the network usually binds the network variables and selects the domain number • Tools do the rest: • Give subnet and node ID’s to new nodes • Choose the transportation service (node or group sending acknowledged, repeated, unacknowledged, etc...) • Give group addresses and send all messages required for configuring the address tables • Maintain a database about all nodes and connections

  17. Designing LON networks

  18. Different transceivers and their most common usage environments • RS-485; intradevice buses • FTT-10A; most common transceiver in buildings • LPT-10; nodes with low power consumption, like displays and keyboards • TPT-1250; backbone channels in buildings etc. • PLT-10; electricity networks of facilities in US • PLT-22; electricity networks of facilities in Europe • PLT-30; electricity networks of electrical power plants

  19. Termination Bus cable BUS Connection stub COMBINATION (= free) RING (=free) STAR (=free) Topologies of FTT-10 and LPT-10 segments

  20. FT-10/FT-10 router Termination FT-10 -channel FT-10 -channel Max numbers: 64 pcs/segment 127 pcs/channel FT-10 -channel FT-10 channel Topology of a large network

  21. Terminations • Terminations are needed to achieve adequate impedance adaptation • Changes in impedance cause reflections • In free topology impedance relations are always vague, and the termination can offer only a partial fix • It is recommended to strive for bus-like topology, with terminations at each ending, in order to achieve good conditions for successful data transmission.

  22. Properties of channel types Distances in the worst case, with the most suitable twisted pair cable, bandwidth with 12 bytes / package

  23. Example calculation of bandwidth (worst case) • 60 nodes in FTT-10 channel, theoretical bandwidth 320 packages per second • Approximately 8 network variables from each node are bound to other nodes using acknowledged service: 8 x 2 = 16 pcts • Transmit frequency maximum 1 minute and minimum 5 seconds is estimated to approximately 40 seconds • Total packets/minute: 60 nodes x 16 pct/node x 60 s/min / 40 s = 1440 pcts/minute • In addition traffic caused by control room in worst case: approximately 10 messages from each node every 30 seconds by control room: 60 nodes x 10 messages/node x 2 packets/message x 60 s/min / 30 s = 2400 pcts/minute • Total: 1440 + 2400 = 3840 packets /minute = 64 pcts/s • Bandwidth usage 64 pcts/s / 320 pcts/s = 20 % => OK!

  24. Cable type properties

  25. Maximum lengths of FTT-10 segments with different cable types

  26. Noise shielding of cabling • Evenness of pair twist is important in cables • Unsymmetrical resistance and capacitance are electric characteristics affecting noise shielding • When cables are ended, mantles are peeled and twists are opened as little as possible • LON cables are located as far as possible from power lines • When using shielded cables shielding is connected reliably over couplings and grounded from other end only (to avoid ground loops)

  27. Basic instructions for network design • Don’t design too large networks (e.g. do not design several facilities in one network) • Don’t chain routers unnecessarily • Leave plenty of room for extension in node number, cable length and bandwidth • Bus-topology two-termination cabling is the most reliable alternative for data transmission • Place nodes that frequently ”talk” to each other in the same channel • Don’t mix unnecessarily the systems belonging to the facility with those related to an organization

  28. Basic instructions for network design • Don’t mix unnecessarily the systems belonging to the facility with those related to an organization • Temperature variations decrease maximum distances • Uneven distribution of nodes in the LON network decreases maximum distances • Unshielded power supply of frequency converters is typical source of disturbance

  29. Documentation of LON network • Network scheme showing channels and location of routers belonging to LON network • Channel schemes (in layouts) showing route of segments belonging to channel and location of repeaters, routers, transformers, batteries,UPS’es and bus terminations • More detailed drawings clarify affiliation of LON devices to segments and affiliation of sensors and actuators to LON nodes and power supplies • Each screw connector in the system must be numbered and documented, so that system can be maintained • In design phase it is important to decide and document descriptive names for nodes, which are then used when installing the LON network and building the graphical user interface (GUI)