Publication 1756-UM050A-EN-P - December 2001
1-4 About the 1756-ENBT Module
Use of the Control and
Information Protocol (CIP)
The 1756-ENBT module uses the Control and Information Protocol
(CIP). CIP is the application layer protocol specified for EtherNet/IP,
the Ethernet Industrial Protocol, as well as for ControlNet and
DeviceNet. It is a message-based protocol that implements a relative
path to send a message from the “producing” device in a system to the
“consuming” devices.
The producing device contains the path information that steers the
message along the proper route to reach its consumers. Since the
producing device holds this information, other devices along the path
simply pass this information; they do not need to store it. This has two
significant benefits:
• You do not need to configure routing tables in the bridging
module, which greatly simplifies maintenance and module
replacement.
• You maintain full control over the route taken by each message,
which enables you to select alternative paths for the same end
device.
Understanding the
Producer/Consumer Model
CIP uses the “producer/consumer” networking model, replacing the
old 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 (“multicast”) their data either upon
a change of state (COS) or periodically. 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 ControlLogix backplane and over the EtherNet/IP network.
This data exchange conforms to the producer/consumer model.
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