LONWORKS® Technology

The LonTalk Protocol


The LonTalk protocol is a collection of services that supports reliable communication among nodes and makes efficient use of the communications medium. Conformance with the LonTalk protocol provides three primary benefits:

  • Insulates the developer of LONWORKS-compatible products from the detailed design of reliably moving information throughout a local operating network.
  • Provides installers of LONWORKS networks enormous flexibility in selecting and configuring nodes to meet a particular application.
  • Ensures the predictability of network behaviour under all conditions.

The LonTalk protocol has been designed for applications involving sense, monitor, control and identification functions.

The LonTalk Protocol - Key Features


The LonTalk protocol supports end-to-end acknowledgements with automatic retries. When this service is used, a node sending a message will expect an acknowledgement from all intended receivers and will automatically retransmit the message unless all intended receivers respond. Alternatively, a programmed pulse timer technique, in which nodes notify the network of their presence at predetermined intervals, assuring reliable communication. Absence of an acknowledgement, or a pulse, can be used to trigger an alarm condition.

Variety of communications media

The LonTalk protocol supports communications on a variety of wired and wireless media, including:

  • Twisted pair
  • Power line (powered or unpowered)
  • Radio frequency
  • Coaxial cabling
  • Fibre optics

Response time

The LonTalk protocol uses a proprietary collision prediction algorithm that permits a channel to carry its maximum capacity, rather than have its throughput degrade due to excess collisions (as, for example, happens with Ethernet). In addition, collision detection is optionally supported on certain media, including twisted-pair; this further enhances response time in cases where collisions do occur. At the fastest LonTalk data rate of 1.25 million bits/second, the LonTalk protocol supports over 500 transactions per second. For applications that must limit the maximum delay incurred by nodes with high-priority messages, the LonTalk protocol offers an optional priority feature. Using priority, the highest priority node is guaranteed access to the medium as soon as transmission of any message in progress is completed.

Low product cost

Many LON nodes are small, simple devices: light switches, temperature sensors, on-off controls, etc. Such devices cannot tolerate substantial increases in size and cost. The LonTalk protocol has been designed for implementation using a single, low-cost, VLSI chip that can be economically and practically incorporated in these low-cost devices.


A major goal of the LonTalk protocol is to give system integrator designers and clients the ability to select from the same or different companies, the ability to design products that will be able to interact with one another. The LonTalk protocol provides a common applications framework that ensures interoperability using powerful concepts called network variables and Standard Network Variable Types (SNVTs). Interoperability is further assured with the LONMARK® certification program. Functional device models have been developed by the LONMARK Interoperability Association to assure plug and play compatibility. As Davmark Group is a partner in the LONMARK Association, we can apply intelligent Technologies to making you dreams a reality, as an invisible service, which just works, the way you want it to work, when you want it to.

LonTalk Protocol Capacities

Network Size

Subnets per domain: 255
Nodes per subnet: 127
Nodes per domain: 32,385
Groups per domain: 255
Nodes per group: * 63
Number of domains: 281,474,976,710,656

*For acknowledged service. No node limit for unacknowledged service.

LonTalk Protocol Services

The LonTalk protocol design follows the International Standards Organization's Reference Model for Open Systems Interconnection (ISO OSI), which prescribes the structure for open communications protocols. LONWORKS is unique in that it is the only control protocol that implements all seven layers of this model. For a more detailed discussion of this communications model, please see the OSI reference model page.

The LonTalk protocol supports many different types of communications services. This means the system can be tailored to meet your requirements. All of these services are selected at the time of node installation with network management software. The various services below are briefly described:

  • Unacknowledged - Unacknowledged is the most commonly used message service. In this mode, system nodes send out messages on the network whenever the local application determines it appropriate. The node that sent the message does not listen for responses from receiving nodes. This service provides the widest network bandwidth.
  • Unacknowledged/Repeated - This service is similar to acknowledged service, but does not receive confirmation of receipt from the receiver. Instead, the message is sent a number of times determined at the time of node installation on a network variable basis.
  • Acknowledged - Acknowledged service is used when it is critical that a message be received at its intended destination. The retry time-out is set at the time of installation when the node is installed and when SNVTs are bound between nodes. The network management software (for example, ICELAN) sets all of the timers in the Neuron Chip according to the network design. This service will reduce available bandwidth on the network.
  • Priority - You can allocate priority time slots on a channel to improve the response time of critical packets. This ensures that one and only one node is assigned to a particular priority slot. This service reduces communication bandwidth and should be used sparingly.

The important point to derive from this discussion is an awareness of the architectural issues associated with various network protocols. For example, the CAN (Control Area Network) protocol used by DeviceNet and SDS is only a sensor bus, not a full network implementation. This means that routers and multiple communication media types cannot be supported by these sensor bus technologies. While this may be fine for some applications, there are clearly limitations if the technology were to be implemented on a plant wide basis.

Network Management Services

LonTalk Network Management Services are a formal part of the LonTalk protocol. Support for these services is contained in every LONWORKS node. This guarantees that all nodes, regardless of origin, can respond to LonTalk commands from nodes designed to perform network management functions. Below is a partial list of services supported by network management messages:

  • Find unconfigured nodes and download network addresses.
  • Stop, start and reset node applications
  • Configure routers and bridges
  • Download new application programs
  • Change the network variable configuration table:
    • The type of protocol service used to send the network variable, and if the variable is sent in a priority slot.


We hope this has been a useful introduction to Echelon Corporation’s LONWORKS® technology, and not too technical.

Davmark Group make things work. We do the hard work, not you.

Davmark Group provides advanced solutions using LONWORKS.

Extensive portions of this article were quoted verbatim from Motorola document BR1108/D, LONWORKS Product Line Brief and EB161/D, LonTalk Protocol. Davmark Group wishes to express their grateful acknowledgment to both Echelon and Motorola Semiconductor for these reference documents.


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