Message Types
Original instructions
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Overview
Two types of industrial Ethernet message types are supported by the Ethernet communication module:
Message Type
Includes...
Explicit
  • Non-time critical management data
  • Read/write application data
Implicit
  • Real-time I/O data
  • Real-time control data
  • Real-time synchronization data
Explicit Messages
Explicit messages transmit information used for device configuration and diagnostics, and for data collection. In explicit messaging, the client issues a request; the server receives, processes, and sends a response back to the client.
You can specify a response timeout value, indicating how long the client waits for a response from the server. If the client does not receive a response from the server within the response timeout period, the client reissues its request. The length of the response timeout will vary depending on the requirements of your application.
Examples of explicit messages include: SNMP messages, FTP messages, CIP establish connection messages, EtherNet/IP query and response messages, and DHCP messages.
The characteristics of explicit messaging are:
Explicit messages can be sent as either connected or unconnected, depending on the frequency of your need for data, and on the level of service required:
Message type
Characteristics
Connected
  • Begins when an originating device initiates a connection by sending a request to a target device.
  • The connection is established when the originator receives a successful response from the target.
  • A CIP connected message has a higher priority and provides better service, but requires a greater amount of resources from both the target and originator devices.
  • Used for recurring requests, and for high priority parameter monitoring.
  • Typically use short response timeout settings.
Unconnected
  • Less resource intensive.
  • Used for less frequent requests, and for lower priority parameter monitoring.
  • Typically use very long response timeout settings.
NOTE: The response timeout can be configured using the EM Request Timeout parameter (located in the Channel Properties → EtherNet/IP page).
Implicit Messages
Implicit messages consist of packets of data that are time critical. Implicit messages are used for real-time control and synchronization. Examples of implicit messages include: real-time I/O data, motion control data, functional diagnostic data, real-time synchronization data, and network topology management data.
Implicit messages require determinism and high performance in message processing and delivery.
The characteristics of implicit messaging are: