4 - communicate over networks, The safety network, Managing the safety network number (snn) – Rockwell Automation 1768-L45S Compact GuardLogix Controllers User Manual
Page 39: Chapter 4, Communicate over networks, Managing the safety network, Chapter
Rockwell Automation Publication 1768-UM002C-EN-P - April 2012
39
Chapter
4
Communicate over Networks
The Safety Network
The CIP Safety protocol is an end-node to end-node safety protocol that allows
routing of CIP Safety messages to and from CIP Safety devices through bridges,
switches, and routers.
To maintain high integrity when routing through standard bridges, switches, or
routers, each end node within a routable CIP Safety Control System must have a
unique reference. This unique reference is a combination of a safety network
number (SNN) and the node address of the network device.
Managing the Safety Network Number (SNN)
The SNN assigned to safety devices on a network segment must be unique. You
must be sure that a unique SNN is assigned to each CIP Safety network that
contains safety devices.
The SNN can be software-assigned (time-based) or user-assigned (manual).
These two formats of the SNN are described in the following sections.
Topic
Page
Standard DeviceNet Communication
TIP
Multiple safety network numbers can be assigned to a CIP Safety subnet or
a ControlBus chassis that contains more than one safety device. However,
for simplicity, we recommend that each CIP Safety subnet have
one, and only one, unique SNN.