Installation guide

Network Infrastructure for EtherNet/IP™

Understanding the Basics of Network Protocols

2-11

processing systems. Office network examples are file, print, mail, and database servers. Examples related

to EtherNet/IP networks are DHCP/BOOTP, DNS, and web servers.

Publish-subscribe communication is a one-to-many model. In these systems, devices subscribe to data

they need and publish information they produce. Common examples of publish-subscribe systems include

newspapers, magazines, cable television, and various multimedia information services available over the

Internet, such as breaking news. The publish-subscribe model is used in some control networks for

periodic broadcasts of relatively large amounts of data (e.g., 1000 bytes).

Producer-consumer communication also is a one-to-many model. Information produced by one device

can be consumed by a group of other devices. In comparison with the models mentioned above, the

producer-consumer model is the most applicable for I/O messaging (transport classes 0 and 1) on

EtherNet/IP, which includes cyclic and change-of-state event-type messages, message size, and rate.

Refer to The EtherNet/IP™ Specification

for more details.

Advantages of the Producer-Consumer Model

The primary benefit of a producer-consumer network is its more efficient use of bandwidth. When a

message is produced onto the network, it is identified not by its destination address, but by its

connection ID. Multiple nodes may then consume the data to which the connection ID refers. As a

result, if a node wants to receive data, it only needs to ask for it once in order to consume the data

each time it is produced. And, if a second (third, fourth, etc.) node wants the same data, all it needs

to know is the connection ID to receive the same data simultaneously with all other nodes.

Conversely, using the source-destination model, nodes receive only the packets that contain their

destination node number. If more than one node needs the same data, it must be transmitted multiple

times, which is inherently inefficient. This can also cause synchronization problems as nodes that

require the same data obtain it at slightly different times.

ODVA, The CIP Networks Library, Vol. 1 and 2, The EtherNet/IP™ Specification. Ann Arbor: ODVA, Inc., 2006.