LON Technology

Some Information about LON

LON is a control network for universal use developed by Echelon Corporation, USA. It is a distributed automation system where free programmable intelligent nodes communicate using the standardized LonTalk® protocol (ISO/IEC 14908-1). The nodes exchange status and control messages in any topology and via various media realizing the desired control applications by interacting. Thereby the entire system remains modular and flexible. Furthermore the software of a node remains slight and manageable.

Interoperability, meaning the seamless integration of products from several manufacturers, is a major subject of LON technology. This was reached by using a single microprocessor –the NEURON Chip®– not only providing a standardized communication interface but also realizing the basic communication. Disclosure of the communication protocol in the ANSI / ISO/IEC 14908-1 standard and continuative standards defined an open standardized system, for which components are available from manufacturers all over the world.

What Makes the Difference?

The difference in comparison with other field bus systems becomes obvious in the technological approach: Distributing the control task by using rules partly realized in hardware is a general approach not emerging from the solution for a single area of application. This results in a universal usability for a general and very broad range of requirements. For extreme requirements and special challenges LON often is inappropriate. There specific solutions are unbeatable, however rarely transposable.

In building automation this becomes apparent. LON crosses the traditional barriers between different building sections (heating, lighting, …) to the advantage of a cross-functional building automation. LON devices complete the control tasks in their application section but, at the same time, make available information to devices dedicated to other application sections, thus increasing the effective-ness of the whole automation system. The important thing in this is not being open for information transfer but the integrated operation of the networked system. Without any change in technology all tasks can be solved using products from different manufacturers. The message from the access control at the gate is just a data point, which next to granting access can as well be used by the room heating resulting in a comfortable office temperature as soon as the staff member reaches the office. Separate presence detection is not required. Initial costs of such integrated solutions may be higher than those for traditional ones, total cost of ownership will soon make up for it.

LON Characteristics

  • Standardized and already implemented communication
  • Manageable software by distribution of the control task
  • Easy modification and scalability
  • Free choice of topology
  • Safe local operation by independence from a central instance
  • Variety of transmission media
  • Communication distance
  • Flexible addressing
  • Interoperability

The Elements of LON

Network Nodes

The NEURON Chip is the core of the node intelligence, where arbitrary applications can be loaded. If required, external memory can be added. Each NEURON and herewith each network node can be identified by its unique, 48 bit NEURON-ID. In addition the NEURON ensures communication handling by the implemented LonTalk protocol.

Following the disclosure of the LonTalk protocol in the ISO/IEC 14908-1 standard it is possible to develop devices for this network technology using different processors. Normally an FPGA or ASIC is used on the device to access the network; the higher protocol layers are then realized in PC software. This allows, further to higher performance, to overcome other resource restric-tions. PC–network interfaces, routers and nodes with special performance requirements are typical fields of application. The Easylon+ products, for instance, make use of these possibilities.

Transceiver

A transceiver couples the node to the network. As large as the variety of the media is which LON can use (the technology is by definition not restricted to certain media) as large is the number of different transceiv-ers. Very common is the TP/FT-10 transceiver, as twisted pair lines in free topology are frequently used (TP/FT-10 networks).

Lontalk Portocol

This is the LON “language”. It is used with all nodes and is already implemented in the NEURON Chip. (s. a. Standards)

Tools For Operation and Development

A network management tool is required to design and maintain a LON network. Almost all current tools are based on the LNS (LON Network Services) platform by Echelon. A network management tool serves for planning the network and establishing the logical connections between the nodes – the binding. Furthermore it allows network diagnosis and provides information visualization systems can use.

For the development of the nodes themselves Echelon provides the “NodeBuilder” software. This program allows application writing using the NEURON-C programming language. Similar to C this language contains special extensions with respect to the LON communication protocol and enables a quick implementation of control applications.

Interoperability

The standardized protocol in itself is not sufficient. Standard network variable type tables (SNVT) are part of the LON technology. With respect to applications, LonMark International coordinates the definition of functional profiles existing for many areas of application.

The NEURON Chip is the core of the node intelligence, where arbitrary applications can be loaded. If required, external memory can be added. Each NEURON and herewith each network node can be identified by its unique, 48 bit NEURON-ID. In addition the NEURON ensures communication handling by the implemented LonTalk protocol.

Following the disclosure of the LonTalk protocol in the ISO/IEC 14908-1 standard it is possible to develop devices for this network technology using different processors. Normally an FPGA or ASIC is used on the device to access the network; the higher protocol layers are then realized in PC software. This allows, further to higher performance, to overcome other resource restric-tions. PC–network interfaces, routers and nodes with special performance requirements are typical fields of application. The Easylon + products, for instance, make use of these possibilities.

Transceiver

A transceiver couples the node to the network. As large as the variety of the media is which LON can use (the technology is by definition not restricted to certain media) as large is the number of different transceiv-ers. Very common is the TP/FT-10 transceiver, as twisted pair lines in free topology are frequently used (TP/FT-10 networks).

Lontalk Portocol

This is the LON “language”. It is used with all nodes and is already implemented in the NEURON Chip. (s. a. Standards)

Tools For Operation and Development

A network management tool is required to design and maintain a LON network. Almost all current tools are based on the LNS (LON Network Services) platform by Echelon. A network management tool serves for planning the network and establishing the logical connections between the nodes – the binding. Furthermore it allows network diagnosis and provides information visualization systems can use.

For the development of the nodes themselves Echelon provides the “No-deBuilder” software. This program allows application writing using the NEURON-C programming language. Similar to C this language contains special extensions with respect to the LON communication protocol and enables a quick implementation of control applications.

Interoperability

The standardized protocol in itself is not sufficient. Standard network variable type tables (SNVT) are part of the LON technology. With respect to applications, LonMark International coordinates the definition of functional profiles existing for many areas of application. 

The LON-Network Structure

The LON network can be structured in domain, subnet and node. A domain can comprise up to 255 subnets, a subnet a maximum of 127 nodes. In total this makes up to 32 385 nodes in one domain. Several domains can be connected. However, in principle only nodes within the same domain can directly communicate. Each node in the network has a distinct logical address consisting of the three hierarchical levels domain-id, subnet-id and node-id.

A LON network uses infrastructure components such as routers, bridges and repeaters.

Routers are devices offering two or more network connections. They are used to connect different subnets. Messages received from the network on one side will usually be transmitted to the other side and vice versa. Additionally the router can filter messages, distribute messages or find and route into the correct subnet.

Bridges connect different domains. They transmit data from one domain to another and vice versa.

Repeaters just are physical signal amplifiers regardless of the message contents. They are used to realize long communication distances or if the maximum permissible number of 64 nodes per 2-wire-segment (TP/FT-10 transceiver) is exceeded.

Network Topology and Media

LON allows for various network topologies and free selection between bus, star, ring or tree structure. In practice free topologies often are realized, oriented to the existing structures in buildings or installations. For segmentation of such free topologies routers can be used to control the data transfer.

LON is specially flexible with respect to the transmission media:

  • Twisted pair
  • Radio
  • Infra-red
  • Fiber optic cable
  • COAX cable
  • Power supply system
  • IP-networks

Even larger distances can be connected. Networks (in bus topology) can be extended up to more than 2000m using twisted pair lines.

By using physical star couplers for instance, the length of the individual branch lines is 1.3 km maximum. By using repeaters, routers or gateways the structures of the network can be extended to an almost unlimited length.

Further to those transmission media the LonTalk protocol can also use the IP-protocol for transmission. Thus the LonTalk protocol becomes Intranet and Internet enabled.

Who is Addressing Whom?

Further to the mere physical connection the control task requires a logical connection. Data exchange in LON networks takes place between network variables (NV). A special group among these is the SNTVs (Standard Network Variable Type). Defined by LonMark

International every developer can use them to maintain interoperability. Network variables are of special importance:

  • Information from one node to another is exclusively “transmitted” by NVs.
  • NVs are the logical interface from one node to every other node.
  • Binding the NVs of the network nodes is the main task of the system integrator while commissioning the network.
  • NVs are, along with configuration parameters, the essential information, which can be seen of a node.

A network management tool is used to define the control logic of the network. The following definitions are made:

  • Who communicates with whom?
  • Which information is exchanged?
  • In which way is the information exchanged?

The Network is the Control

A LON network consists of up to 32,385 intelligent network nodes communicating via LonTalk. Time-critical messages can be prioritized; a safe transmission is granted, amongst others, by end-to-end control and acknowledgements.

Wherever input and output signals (I/O) are required, distributed and intelligent sensor or actor devices can be placed. Those application specific nodes control and manage themselves and mutually. They only need status or modification messages from other network nodes to take action, which they receive via the LON network. Transmission speeds up to 1.25 Mbps can be reached.

Standardized data types, so-called SNVTs and functional profiles are the basis for the interoperability of the network nodes. The interoperability between modules from different vendors provides the user with freedom of choice and considerably facilitates a cross-functional building automation.

By distributing the intelligence or, respectively, the application LON networks can be operated at low cost without host computer or PLC (for central capturing and processing). No host computer is required for control and monitoring tasks. For visualization purposes and further processing of LON data in other systems usually PCs are used.

LON offers a flexible field bus system provided with distributed intelligence that can cover large distances using most different media on a high level of reliability and safety. The modular structure allows for modification and extension of the network; at any time and without large effort.

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LON Related Standards

  • EN 14908; ISO/IEC 14908 Open data communication in building automation, controls and building management
    - Part 1: Protocol Stack
    - Part 2: Twisted Pair Communication
    - Part 3: Power Line Channel Specification
    - Part 4: IP Communication
    - Part 5:  Implementation
    - Part 6: Application elements