User manual

218 Publication ENET-UM001I-EN-P - January 2010
Appendix D EtherNet/IP Network Overview
Use of the Common Industrial Protocol (CIP)
The EtherNet/IP communication modules use the Common Industrial
Protocol (CIP). CIP is the application layer protocol specified for
EtherNet/IP, the Ethernet Industrial Protocol, as well as for ControlNet and
DeviceNet.
CIP is a message-based protocol that implemen
ts a relative path to send a
message from the producing module in a system to the consuming modules.
The producing module contains the path information that steers the message
along
the proper route to reach its consumers. Since the producing module
holds this information, other modules along the path simply pass it along
because they do not need to store the information. This information handling
has two significant benefits.
• You do not need to configure routing tables in the bridging module,
whic
h greatly simplifies maintenance and module replacement.
• You maintain full control over the route taken by each message, which
enab
les you to select alternative paths for the same end module.
CIP uses the producer/consumer networking model instead of a
sourc
e/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
Simple network management
protocol (SNMP)
SNMP is a standard for network management within TCP/IP environments. This protocol enables client
applications monitor and manage network information on host computers and gateways. This protocol
is password-protected.
SNMP uses a distributed architecture consisting of management systems and agents. Data is
passed
from SNMP a
gents, which are hardware or software processes reporting activity in each network
module (switch, router or bridge) to the workstation console used to oversee the network. The agents
return information contained in a management information base (MIB), which is a data structure that
defines what is obtainable from the module and what can be controlled.
Internet Group Management
protocol (IGMP) snooping
IGMP snooping enables switches to route multicast traffic by distributing each packe
t only
to the ports
that need to receive it. Many switches support this feature. However, for IGMP snooping to work, most
of these switches require a system router. If your control system is a stand-alone network or is required
to continue performing if the router is out of service, make sure the switch you are using supports IGMP
snooping without a router present.
This feature is highly recommended for EtherNet/IP s
ystems th
e control I/O.
Protocol Descriptions
Protocol Desc
ription