Network Topologies
3.3 Ring Topology
SIMATIC NET PROFIBUS, Optical Link Module
12
Operating Instructions, 07/2008, A2B00065774O, Edition V1.5
3.3
Ring Topology
Figure
3-3
Network structure with a redundant optical ring topology
This network topology is a special form of the bus topology.
“C
losing
”
the optical
bus achieves high operational reliability in the network. A redundant optical ring
can only be implemented using modules with two optical channels.
Monitoring mechanisms:
•
Send echo:
yes
•
Monitor echo:
yes
•
Suppress echo:
yes
•
Segmentation:
yes
The interruption of one or both fiber-optic cables between the modules is detected
by the OLM and the ring becomes an optical bus.
If one module fails, only the DTEs connected to this module or the RS-485
segment are disconnected from the ring. The rest of the network itself stays
functional as a bus. The problem is indicated by the LEDs of the two OLMs
connected to the disrupted fiber-optic link and by the signaling contacts of these
OLMs. The segmentation is canceled automatically as soon as both modules
recognize that the segmented fieldbus (sub)network is no longer disrupted based
on test frames that they send out automatically. The bus then closes again to form
a ring.
Ch 1
Ch 2
S E
Ch 3
S E
OLM/P1
2
OLM/G1
2
(-1300)
Ch 1
Ch 2
S E
Ch 3
S E
OLM/P1
2
OLM/G1
2
(-1300)
Ch 1
Ch 2
S E
Ch 3
S E
OLM/P1
2
OLM/G1
2
(-1300)
DTE/
bus segment
DTE/
bus segment
DTE/
bus segment
DTE/
bus segment
FOC
RS-485
Ch 1
Ch 2
S E
Ch 3
S E
OLM/P1
2
OLM/G1
2
(-1300)
