Rockwell Automation Ethernet Design Considerations Reference Manual - Manual (Page 14)

14 Rockwell Automation Publication ENET-RM002C-EN-P - May 2013
Chapter 1 EtherNet/IP Overview
Network Protocols On the most basic level, Ethernet is a wire or cable that connects computers and
peripheral modules so that they can communicate. The actual wire used for the
network is referred to as the network medium. Beyond the physical medium, all
Ethernet networks support protocols that provide data transfer and network
management capability.
CIP
CIP is a message-based, application-layer protocol. This protocol implements a
relative path to send a message from the producing modules in a system to the
consuming modules.
CIP uses the producer/consumer networking model instead of a source/
destination (master/slave) model. The producer/consumer model reduces
network traffic and increases speed of transmission.
In traditional I/O systems, controllers poll input modules to obtain their input
status. In the CIP system, digital input modules are not polled by a controller.
Instead, they produce their data either upon a change of state (COS) or at a
requested packet interval (RPI). The frequency of update depends upon the
options chosen during configuration and where on the network the input
module resides. The input module, therefore, is a producer of input data and the
controller is a consumer of the data.
The controller can also produce data for other controllers to consume. The
produced and consumed data is accessible by multiple controllers over the Logix
backplane and over the EtherNet/IP network. This data exchange conforms to
the producer/consumer model.
Protocol Description
Common Industrial
Protocol (CIP) CIP applies a common application layer over an Ethernet network by encapsulating
messages in TCP/UDP/IP. This common application layer provides interoperability and
interchangeability of industrial automation and control modules on an Ethernet network.
The EtherNet/IP network supports both real-time I/O (implicit messaging) and explicit
messaging.
Transmission Control
Protocol/internet Protocol
(TCP/IP) TCP/IP is a transport-layer protocol (TCP) and a network-layer protocol (IP) commonly
used in business environments for communication within networks and across
internetworks. The EtherNet/IP communication modules use TCP/IP for explicit
messaging. Explicit messaging is used by applications when time is not a critical factor,
such as uploading or downloading programs.
User Datagram Protocol/
internet Protocol (UDP/IP) UDP is a much simpler transport protocol. It is connectionless, and provides a simple
means of sending datagrams between two modules. UDP is used by applications that
implement their own handshaking between modules and require minimal transport
service. UDP is smaller, simpler, and faster than TCP and can operate in unicast, multicast,
or broadcast mode. The EtherNet/IP communication modules use UDP/IP for real-time
I/O messaging.