Rockwell Automation Ethernet Design Considerations Reference Manual - Manual (Page 61)

Rockwell Automation Publication ENET-RM002C-EN-P - May 2013 61
EtherNet/IP Protocol Chapter 4
These example applications describe how connections are used.
Terminology
The terms in this table help you understand connections.
EXAMPLE I/O Connections
A Logix5000 controller has five CIP I/O connections to modules in a remote
chassis and all of these connections are through the same local 1756-EN2T
module and the same remote 1756-EN2T module.
The following connections exist:
• One TCP connection
• Five CIP connections
EXAMPLE RSLinx OPC Test Client
The following connections exist:
• One TCP connection
• Four CIP connections (four is the default)
Table 8 - EtherNet/IP Connection Terminology
Term Definition
Producer and
consumer Producer/consumer refers to implicit connections. With implicit connections, messages are sent cyclically (every RPI).
EXAMPLE: Assume a ControlLogix controller is controlling a single rack of FLEX I/O with a rack connection. Both the ENBT module that is local to the
controller and the FLEX AENT module are consumers and producers of data. The AENT consumes outputs and produces inputs.
Client and server Client/server refers to explicit connections. A client creates a connection and initiates messages. A server provides a service or data. Clients can send
messages continuously or intermittently.
EXAMPLE: A ControlLogix controller can send a MSG instruction to another controller.
Transports Each connection has transports. A transport is a uni-directional entity with its own numeric identifier. An implicit connection has 2 transports. An explicit
connection has 1 transport. Transports are important because they help you calculate the number of packets per second for each Ethernet interface.
EXAMPLE: I/O
For an I/O connection to a rack of distributed I/O, a connection is configured in the Logix Designer application by adding the communication adapter and I/O
modules in the I/O list. When the connection is created, output packets flow from the controller to the I/O rack. In addition, input packets flow from the I/O
to the controller. Each direction of flow is a transport. In this example, two transports exist. One transport is from the controller to the adapter. The second
transport is from the adapter to the controller.
EXAMPLE: Produced Tag
For a multicast produced tag connection with two consumers, there is a connection to each consumer. Data from the producer is produced to the wire on one
transport. Each of the consumers returns a heartbeat. A total of three transports exist in this example. One transport is from the tag producing controller to
the ‘wire’ media. The second transport is from one consumer to the tag producer. The third transport is from the second consumer.
UCMM In the web servers, you can see references to Unconnected Message Manager (UCMM). This type of messaging is momentary and therefore can be ignored
unless you are troubleshooting. Examples of where UCMM messages are used are:
• Update of module firmware
• Some functions in RSLinx software
• CIP Generic MSG instruction
• Opening any CIP connection (forward_open command)