Industrial Ethernet

The case for Industrial Ethernet III: EtherNet/IP™

Author: Clark Hummel | December 6, 2011

The last post in this series we examined the major protocols used for automation and control in industrial Ethernet networks.  Today we will examine the protocol with highest percentage of industry usage: EtherNet Industrial Protocol, or EtherNet/IP™.
EtherNet/IP™ was introduced by Rockwell Automation in 2001. Over the last 9 years it has grown into the most widely used industrial Ethernet solution for factory automation. EtherNet/IP provides a complete set of services and messages for applications such as:

  • Control
  • Safety
  • Synchronization
  • Motion
  • Data exchange

Advantages

  • Common interoperability with  Rockwell/Allen-Bradley control systems.
  • Ready availability of devices (I/O  modules, controllers, drives, gateways etc;)
  • Use of off-the-shelf Ethernet  hardware such as routers, switches, cabling)
  • Ease of system integration using  the CIP (Common Industrial Protocol)
  • EtherNet/IP™ is a standard. The  group managing EIP, the Open  DeviceNet Vendors Association (ODVA) ensures a  consistent, comprehensive standard that applies to all EtherNet/IP™ vendors and products.

Basic functional overview

EtherNet/IP™, like other CIP networks, follows the Open Systems Interconnection (OSI) model. The OSI model defines a standardized framework for implementing networking. A typical EtherNet/IP™ network is shown in Figure 1.

Figure 1: Typical Ethernet/IP™ network

Messages

EtherNet/IP™ uses two types of message connections, Explicit and Implicit.

  1. Explicit  connections enable request-response transactions between two  nodes which are general purpose in in nature. Explicit connections  use TCP/IP services to transfer messages across Ethernet. Explicit messages are asynchronous and are sent as needed.
  2. Implicit (I/O data) connections facilitate the movement of application specific messages at regular intervals.  Implicit connections usually use a one-to-many relationship to make full use of multicast messaging over UDP/IP. Implicit messages must be configured to define the data transferred.

 Device classes

EtherNet/IP™ uses three device classes to define the function of the device based upon network communications capability. These classes are defined as: Message Class, Adapter Class and Scanner Class.

  1. Message  Class devices support explicit messages that are sent or  received by all other classes of devices. While they may be the target or originator of explicit message requests, the cannot send  or receive real-time I/O data. Message Class devices include:
    1. PC  interface cards used to up/download programs to PLCs or Host HMI  products
    2. Software  applications not requiring real time I/O data
    3. Network  configuration and diagnostic tools
  1. Adapter  Class devices are the target or real-time I/O data requests from scanner class devices, as well as explicit messaging requests from  all other classes of device. Adapter Class products include:
    1. Drives and modules that send/receive I/O data at the request of PLCs and other controllers
    2. Drives and modules that send/receive explicit messages to and from Message and Adapter class devices
    3. HMI devices that send/receive explicit or implicit messages to/from PLCs
  2. Scanner Class devices are the originator of I/O data connection requests to Adapter Class and other Scanner Class devices. Devices include:
    1. PLCs and controllers that send/receive I/O data at the request of PLCs, Host HMIs and other controllers
    2. PLCs that send/receive explicit messages to and from other PLCs
    3. PC interface cards or software used for PC-based control

Object Model

EtherNet/IP™ uses standard CIP objects. An object class represents a grouping of related attributes. There are three classes of objects:

  1. Required objects: These objects are required by the CIP specification in every EtherNet/IP™ device. These are:
  1. Identity object: contains attributes which includes information such as Vendor ID, Date of Manufacture, Serial number and etc.
  2. TCP or Router object: contains routing information for messaging such as the IP address, gateway, subnet mask.
  3. Ethernet link or network object: hold the physical connection data such as the MAC-ID, interface speed, etc.
  1. Application objects which contain data specific to the device itself.
  2. Vendor specific objects which contain attributes specific to the features and functionality unique to the device such as configuration data, control commands, register data and etc.

Conclusion

EtherNet/IP™ is a standardized, certifiable protocol with a massive industry presence. Implementing EtherNet/IP™ into new network designs is not without it’s challenges, as implementation requires skill and training in both the IT and Automation fields. In the end though, the advantages, savings, and system interoperability and reliability may be worth the transition.

For more information on products supporting EtherNet/IP™ please vist https://www.imshome.com/products/ethernet/ethernet_ip.html

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