A LONWORKS® Technology Tutorial

Introduction

Local Operating Network (LON) technology makes possible a new generation of smart, low-cost products that communicate with one another. It is now possible to create affordable networks of intelligent devices that sense, process, communicate, and control a multitude of applications ranging from handheld instruments to large process control systems. Products can be linked together to serve applications in consumer electronics, factory automation, commercial building controls, vehicle controls, home automation and many other industries.

Industry leaders have dubbed LONWORKS technology the most significant development in semiconductors since the microprocessor. A brief review of its potential application areas reveals why. LONWORKS technology can control and link factory conveyor belts, product inventory, and distribution systems for optimum efficiency and flexibility. Performance and fault diagnosis information for computing and communications equipment can be readily available through onboard and in-box modules powered by Neuron® Chips. Smart office buildings can turn lights on and off, open and lock doors, start and stop elevators, and connect all functions to a central security system. Homeowners can program a vast array of products and conveniences, from sprinkler systems to VCRs, with a touch tone phone from any remote location.

IEC Intelligent Technologies has been developing LONWORKS technology applications for over nine years, and was a LONWORKS Independent Developer for over six years. As the result of this extensive background in applying LONWORKS technology solutions to problems in the real world, products and services from IEC can make almost any LONWORKS application simply better. The purpose of this tutorial is to help increase your understanding of basic LONWORKS concepts.

Local Operating Network (LON) technology makes possible a new generation of smart, low-cost products that communicate with one another. The concepts presented here are brought to life in an actual installation in a Demonstration Project in southern California.

Local Operating Networks

A local operating network consists of intelligent devices, or nodes, that are connected by one or more communications media and that communicate with one another using a common protocol. Nodes are programmed to send messages to one another in response to changes in various conditions and to take action in response to messages they receive.

The nodes on a LON may be thought of as objects that respond to various inputs and produce desired outputs. Linking the inputs and outputs of network objects enables the network to perform applications. While the function of any particular node may be quite simple, the interaction among nodes enables a local operating network to perform complex tasks. A benefit of local operating networks is that a small number of common node types may be configured to perform a broad spectrum of different functions depending how they are linked in a network.

LONWORKS Overview

LONWORKS offers a complete solution to companies for designing, building and supporting LONs. Products developed using LONWORKS can be easily connected with IEC's ICELAN™ , based on Peak Components. Use IEC's ICELAN™ network management tool to form highly functional, local operating networks that are inexpensive to maintain and expand. In addition, LonTalk®, the protocol used by LONWORKS to standardize communication on the LON, defines a standard way for devices to exchange control and status information. LonTalk enables previously disparate systems and products to interoperate and thereby provide new services and benefits.

Echelon®'s implementation of LON technology is available to anyone.

Echelon has arranged for multiple sourcing of the key elements of LONWORKS, making it possible for any company to manufacture and sell LONWORKS-compatible products.

The major elements of LONWORKS are:

• LonTalk protocol
• Neuron chips
• LONWORKS transceivers
• Network management and applications software

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 behavior under all conditions.

The LonTalk protocol has been designed for applications involving sense, monitor, control and identification functions. This section describes the key features of the LonTalk protocol:

1) Reliability -

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

2) 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
• Fiber optics

3) 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.

4) 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.

5) Interoperability -

A major goal of the LonTalk protocol is to give developers, 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 a partner in the LONMARK Association, IEC Intelligent Technologies has made key contributions to making this a reality.

Network Variables

Communication between nodes on a network takes place using the network variables that are defined in each node. The product developer defines the network variables when the application program is created as part of the Application layer of the protocol. Network variables are shared by multiple nodes. Some nodes may send a network variable while others may receive. By only allowing links between inputs and outputs of the same type, network variables enforce an object-oriented approach to product development. This greatly simplifies the process of developing and managing distributed systems.

Whenever a node program writes a new value into one of its output variables, the new value is propagated across the network to all nodes with input network variables connected to that output network variable. This action is handled by the protocol within the Neuron Chip. The user defines the network variable connections when the nodes are installed on the network using a network configuration tool such as IEC's ICELAN, based on Peak Components.

Standard Network Variable Types

The use of Standard Network Variable Types (SNVTs, pronounced "snivets") contributes to the interoperability of LONWORKS products from different manufacturers. Echelon maintains a growing list of over 100 SNVTs for nearly all physical measurement types including the type of variable such as integer or floating point. For example, a SNVT for continuous level is defined as SNVT_lev_contin.

If all manufacturers use this variable type in their application when a network variable for continuous level is defined, any device reading a continuous level can communicate with other devices on the network that may be using the variable as a sensor output to initiate an actuator. As long as a network input variable and a network output variable are defined with the same SNVT when the developer creates the applications, they can be connected together on the network through a process called binding.

Binding is defined at the time of installation using the ICELAN Windows based graphical installation tool. When you install a node, you specify which network variables are to be connected between nodes. This is easily done by highlighting the output network variable on one node and the input network variable on the node or nodes to be connected. ICELAN makes this easy since the important information in each node is presented graphically through a standard Windows interface. Only network variables of the same SNVT type can be bound together. In other words, a temperature type could not be bound to a pressure type.

The following are examples of SNVTs. A complete list of SNVTs is available from Echelon.

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 "Discussion of the OSI reference model" at the end of this article. The LonTalk protocol supports many different types of communications services so that a system can be tailored to meet your requirements. All of these services are selected at the time of node installation with IEC's ICELAN network management software, based on Peak Components. 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.

LonTalk Addressing

To simplify message routing, the LonTalk protocol defines a hierarchical form of addressing using domain, subnet, and node addresses. This form of addressing can be used to address the entire domain, an individual subnet, or an individual node. In addition, multiple dispersed nodes can be addressed using domain and group addresses.

A channel is the physical transport medium for the LonTalk messages. Every node is physically connected to a channel. The communications medium can be twisted pair, power line, radio frequency, coax or fiber optic media.

A domain is a logical collection of nodes on one or more channels. Communications can only take place among nodes in a common domain; therefore, a domain forms a virtual network. Multiple domains can occupy the same channel, so domains may be used to prevent interference between nodes in different networks. The user can choose domains for nodes at the time of installation with ICELAN. For example, two adjacent buildings using nodes with RF transceivers on the same frequency would be on the same channel, but the installer could configure the nodes in each building to be in different domains to prevent interference between the applications. The user assigns the domain ID at the time of installation.

A subnet is a logical collection of up to 127 nodes within a domain. Up to 255 subnets can be defined within a single domain. All nodes in a subnet must be on the same channel, or on channels connected with bridges. Subnets cannot cross routers. If a node is configured to belong to two domains, it must be assigned to a subnet within each of the domains. All nodes within a domain are typically configured in the same subnet except in the following cases: They are located on different channels with intervening routers. Since subnets cannot cross routers, the nodes must be on different subnets. Configuring the nodes in the same subnet would exceed the maximum number (127) of nodes allowed in a subnet. Multiple subnets may be configured on a set of channels connected by bridges to increase the capacity above 127 nodes. For example, a set of channels connected by bridges with two subnets may have up to 254 nodes.

Every node within a subnet is assigned a unique node number within the subnet.

Groups can also be assigned within a domain. A group is a logical collection of nodes within a domain, but the members do not have to share the same channel as with a subnet. A node can be a member of up to 15 groups. Groups are an efficient way to use network bandwidth for one to many network variable and message tag connections. A single domain can contain up to 256 groups.

Each node has a 48-bit unique ID assigned during manufacture. This ID is typically used as a network address only during installation and configuration. It may also be read and used by application programs as a unique product serial number. With 281,474,976,710,656 possible IDs, every node in a LONWORKS network is sure to have a unique address.

LonTalk Protocol Capacities - Network Size

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

The Neuron Chip

he Neuron Chip is the heart of the LONWORKS technology. LONWORKS nodes usually contain a Neuron Chip to process all LonTalk protocol messages, sense inputs and manipulate outputs, implement application-specific functions and store installation-specific parameters. The integral applications processor means that low cost nodes can be designed with as little as one VLSI device. The customer benefits from this technology because manufacturers are integrating it into their sensors and actuators to provide a wide variety of devices for use in networked applications. A stream of new products from a diverse group of manufacturers is now in development to take advantage of LONWORKS technology for present and future applications.

Each Neuron chip has three resident 8-bit processors: two processors dedicated to LonTalk protocol processing, and a third dedicated to the node's application program. Neuron chips are manufactured under license by both Motorola and Toshiba, two of the four largest semiconductor manufacturers in the world.

Neuron chips are programmed in Neuron C, which extends ANSI Standard C to support an object-oriented approach to developing distributed applications. Neuron C provides direct support for LONWORKS objects such as network variables and SNVTs. The language also provides a new statement called the "when" statement that is used to schedule execution of user tasks based on predefined and user-defined events. In addition, Neuron C provides a syntax for declaring a wide range of I/O objects that are supported by the Neuron Chip application I/O hardware.

All services of Neuron C leverage the run-time support provided by the Neuron firmware. This firmware contains:

• The LonTalk protocol communications software, including network management functions and network variable processing
• An event driven scheduler
• Run-time support for applications I/O objects
• Arithmetic, logical, conversion and other application routine libraries

LONWORKS Transceivers

• 78 kbps Twisted Pair Transceiver - This transceiver allows you to build networks with distances up to 4600 feet or 1400 meters (worst case) in loop or backbone configurations. It provides transformer isolation between the node and network for high common mode noise rejection.
• 1.25 Mbps Twisted Pair Transceiver - This transceiver provides higher communications rates for distances up to 430 feet or 130 meters (worst case). It also provides transformer isolation between the node and network for high common mode noise rejection.
• Power Line Transceivers - The power line can provide a good solution for network wiring in many applications. It eliminates the need to install additional wiring, significantly reducing installation costs. These transceivers communicates with either a proprietary spread spectrum or a narrow band technology that provides reliable communications for up to 2000 meters on a clear line. Transformers that inhibit transmission can be bridged with a simple passive circuit.
• 78 kbps Twisted Pair, Free Topology Transceiver - This transceiver allows you to build networks of nearly any configuration including bus, star, loop, and mixed configurations. It features low standby power and transformer isolation between the network and the node. Nodes with this transceiver can communicate up to 500 meters (1,600 feet) with no repeater and up to 1,000 meters (3200 feet) with one repeater.
• Link Power Twisted Pair Transceiver - This transceiver provides the same communications capability as the free topology transceiver but adds distributed power capability to the network. Power is distributed over the network from a central power supply.
• Radio Frequency Transceiver - A variety of RF transceivers are available for wireless communications in many different environments. Both licensed and non-licensed versions are available in the 400-470 MHz and 900 MHz bands respectively.

Network Data Rates (packets/second)

Capabilities of the Various Media

* 2700 meters when used on doubly terminated bus.

*** Depends on antenna heights and gains. Line of sight only.

Network Management and Applications Software

Installing a LONWORKS control network is greatly simplified over the traditional network approaches because the products use a standard protocol and are interoperable. The installation process requires you to connect the devices to the physical media and describe which devices need to communicate to each other using IEC's ICELAN installation tool and the information (network variables) to be communicated. You may also need to install a router to interconnect different communications media, extend the range of a network, or to isolate traffic on certain network channels.

Network installations may be divided into two stages:

• Physically connecting the network hardware including the application nodes, the communications media, and any routers if required.
• Installing and binding network variables in the application devices using IEC's ICELAN network management software, based on Peak Components.

Installing a device informs the network database that the device is on the network. This is usually done by pressing the service pin on the physical device and using IEC's ICELAN software to recognize the device.

Binding a network variable tells the device which other devices it should talk to and what information it should share. This is where network variables specified by the device manufacturer are connected between different nodes.

IEC's New ICELAN , based on Peak Components, is the premier, graphically- based network management and control product to support LONWORKS applications. ICELAN is a Windows® based software product suite (Windows 3.1x, Windows for Workgroups, Windows 95 and Windows NT) which is familiar and easy to use. IEC pioneered the interface for the graphical creation and management of LONWORKS networks. ICELAN 2000, based on Peak Components, provides all the functionality required to install, monitor and maintain LONWORKS networks.

We hope this tutorial has been a useful introduction to Echelon Corporation's LONWORKS technology. IEC is dedicated to providing the most advanced solutions for LONWORKS available anywhere. For more information on our products, including free working demonstration copies of our software, you can contact IEC or browse IEC's other World Wide Web pages.

Glossary of LONWORKS Terms

Bridge - A bridge simply forwards all messages that match the domains between the two channels connected to the bridge.

Channel or Segment - A channel or segment is the transmission media that connect devices on the network such as twisted pair 78 kbps or power line carrier.

Device - A device or node is the piece of equipment installed on the network such as a sensor, actuator; or controller.

Domain - A domain is a logical grouping of devices that can communicate with each other over shared resources such as transmission media. Each network must have at least one domain. A domain is identified by a domain ID that can be 0,1,3, or 6 bytes. Larger domain IDs increase network overhead since the domain ID is sent with every message packet.

Groups - A group is a logical collection of nodes within a domain. A group can contain up to 64 nodes. A single domain can contain up to 256 groups.

Location - Locations are convenient subdivisions of a network that contain related sets of application devices and routers. Locations may correspond to physical places. Each network must have at least one location.

Network Variable - A network variable is an object on one node that can be connected to network variables on one or more additional nodes. A node's network variables define its inputs and outputs from a network point of view and allow the sharing of data in a distributed application.

Node - A node is synonymous with device. It may have up to 255 network variables defined. Simple nodes may have up to 62 variables defined.

Repeater- A repeater forwards all messages between the two channels connected to the repeater.

Router - A router connects one segment of a channel to another segment of a channel or two different channels such as twisted pair and power line communications. A configured router sends only messages destined for nodes that are specified in the internal routing table created by a network management tool. A learning router monitors network traffic and learns the network topology at the domain/subnet level. The learning router then uses its knowledge to selectively route packets between channels.

Subnet - A subnet is a logical collection of up to 127 nodes or devices within a domain.

Standard Network Variable (SNVT) - Pronounced "snivet", SNVTs are a set of predefined types of network variables with associated units, such as degrees centigrade, volts, or meters. SNVTs promote interoperability of products from different manufacturers by standardizing the names given to output and input network variables.

Discussion of the OSI Reference Model

The ISO (International Organization for Standardization) developed a standard defining a model for a general purpose data communications architecture.

Each of the seven layers of this model is implemented in the LonTalk protocol. Each has a purpose to make the technology robust and provide room to grow the network. The most important benefit of this approach is that each layer performs services for the next higher layer so that details are hidden to the higher layer. Changes can be made in a layer without changing any of the other layers.

Layer #1: Network Physical Layer - Electrical Interconnect

This layer addresses specifics of wiring and connections. The specification of the 78 kbps twisted pair media with 2000 meter range, 64 nodes per network segment, and network isolation characteristics is an example of one physical layer type of media. LONWORKS technology provides many different communications media options including 1.25 Mbps twisted pair, power line, fiber optic, and RF transceivers. This provides you with a wide range of choices for communicating your data.

Layer #2: Data Link Layer - Media Access and Framing

This layer defines the rules of access to the physical layer. For example, this corresponds to the dial tone on the telephone network. Services provided by this layer include:

• Error Detection (CRC)
• Flexible allocation of bandwidth
• Priority access mechanisms
• Graceful behavior under overload (p-persistent CSMA)
• Message collision avoidance
• Optional collision resolution, collision detection

Layer #3: Network Layer - Destination Addressing

This layer specifies the destination of a message on the network. This corresponds to the area and long distance codes on the telephone network. Services provided by this layer include:

• Contains the node address information
• Provides for routing of messages to segment and control network bandwidth usage

This layer provides many important services such as determining which nodes on the network receive various messages. The ability to provide routers to segment the traffic and communicate between different physical media is part of this service.

Layer #4: Transport Layer - End to End Reliability

This layer establishes the type of services required for the node messages depending on the level of reliability required by the application. The services provided are:

• Broadcast addressing
• Unicast addressing
• Multicast addressing
• Repeated service
• Acknowledged service
• Unacknowledged service
• Duplicate packet detection
• Authentication

The level of service required by the application is established when each node is installed on the network. This is all handled by a network management installation tool, such as ICELAN, and the node's design.

Layer #5: Session Layer - Remote Actions

This layer provides the communications to request action from another node. Examples of the services include:

• Acknowledgment of received message
• Application to application communication
• Retry if the correct response is not received from the remote node
• Request to a destination group and receive individual responses from the group
• Request - response message authentication

Layer #6: Presentation Layer - Data Interpretation

This layer provides translation of the network data for the application. Examples of services provided in this layer include:

• Input, output, and configuration variables for the node
• Standard data representations for physical quantities
• Network variable description

The standard data representations are important to assure interoperability between products from different manufacturers.

Layer #7 Application Layer-Application Compatibility

This layer includes services to simplify development of application programs to interface to specific sensors, actuators, and external microprocessors. The services provided in this layer include the following:

• Memory storage for application program
• Built-in real-time operating system
• Device drivers for the I/O hardware on the Neuron Chip
• Standard Network Variable Types (SNVTs)

Extensive portions of this article were quoted verbatim from Motorola document BR1108/D, "LONWORKS Product Line Brief" and EB161/D, "LonTalk Protocol". The author wishes to express his grateful acknowledgment to both Echelon and Motorola Semiconductor for these invaluable references.