User manual

36 Publication 1756-RM093F-EN-P - January 2010
Chapter 4 CIP Safety and the Safety Network Number
Unique Node Reference
The CIP Safety protocol is an end-node to end-node safety protocol.
The CIP Safety protocol allows the routing of CIP Safety messages to
and from CIP Safety devices through non-certified bridges, switches,
and routers.
To prevent errors in non-certified bridges, switches, or routers from
becoming dangerous, each end node within a routable CIP Safety
control system must have a unique node reference. The unique node
reference is a combination of a safety network number (SNN) and the
node address of the node.
Safety Network Number
The safety network number (SNN) is assigned by software or by the
user. Each CIP Safety network that contains Safety I/O nodes must
have at least one unique SNN. Each ControlBus chassis that contains
one or more safety devices must have at least one unique SNN. Safety
network numbers assigned to each safety network or network sub-net
must be unique.
CIP Safety Example with More Than One SNN
TIP
More than one SNN 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. This is also the case
for each ControlBus chassis.
Router/
Firewall
SNN_1
SNN_3 SNN_5
SNN_2
SNN_4
SNN_6
SNN_7
1756-L62S
1756-LSP
1756-DNB
1756-ENBT
1768-PB3
1768-L43S
1769-ECR
Switch
Switch
CIP Safety I/O
SmartGuard
1756-IB16
1756-DNB
1756-ENBT
1756-OB16
1768-ENBT 1768-ENBT
CIP Safety I/O
CIP Safety I/O
CIP Safety I/O
CIP Safety I/O
CIP Safety I/O
CIP Safety I/O
CIP Safety I/O