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:
The LonTalk protocol has been designed for applications involving sense, monitor, control and identification functions.
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.
The LonTalk protocol supports communications on a variety of wired and wireless media, including:
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.
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.
| 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.
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:
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.
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:
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.