4 - communicate over networks, The safety network, Managing the safety network number (snn) – Rockwell Automation 1756-L7x GuardLogix 5570 Controllers User Manual
Page 43: Chapter 4, Communicate over networks, Managing the safety network, Chapter
Rockwell Automation Publication 1756-UM022A-EN-P - November 2012
43
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 the following:
• Each CIP Safety network that contains safety devices
• Each chassis that contains one or more GuardLogix controllers
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
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.