LonWorks Physical Layers

From AutomationWiki
Jump to: navigation, search

Introduction[edit]

Layer model of LonWorks Technology consists of seven layers which all are implemented in the LonTalk Protocol. Each layer assists in making the technology robust and performs services for the next higher layer so that details are hidden to the higher layer. Changes can be made in a layer without causing any effect on the other layers.

Layer 1: Network Physical Layer[edit]

This layer is for Electrical Interconnect. It addresses specifics of wiring and connections. For example, the specification of the 78 kbps twisted pair media with 2000 meter range, 64 nodes per network segment, and network isolation characteristics is one physical layer type of media. LONWORKS technology supports various communications media options such as 1.25 Mbps twisted pair, power line, fiber optic, and RF transceivers. This presents extensive choices for communicating data.

Layer 2: Data Link Layer[edit]

This layer is for Media Access and Framing. It defines the rules of access to the physical layer and this corresponds to the dial tone on the telephone network. This layer provides following services:

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

Layer 3: Network Layer[edit]

This layer is for Destination Addressing and 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:

  • Node address information
  • Routing of messages to segment and control network bandwidth usage
  • 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.

Layer 4: Transport Layer[edit]

This layer is for End to End Reliability and defines the type of services needed 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

Layer 5: Session Layer[edit]

This layer is for Remote Actions. It provides communications for requesting action from another node. Services offered are:

  • 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[edit]

This layer is for Data Interpretation. Translation of the network data for the application is provided by this layer. Examples of services provided include:

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

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

Layer 7: Application Layer[edit]

This layer is for Application Compatibility. Services to simplify development of application programs to interface to specific sensors, actuators, and external microprocessors are included in application layer. 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)

References[edit]

Intelligent Build