Siemens SIMATIC NET Operating Instructions Manual page 55

Bus topology with fiber-optic link monitoring and segmentation
Use this mode especially when you want a disrupted fiber-optic cable segment to be
separated from the rest of the network, see section "Setting the mode of the electrical
channel (CH1) (Page 23)" or "Setting the mode of the electrical channel (CH0) (Page 24)".
Only use this mode, if you only connect PROFIBUS OLM V4 or V3/V4 to each other.
Monitoring mechanisms
● Send echo: yes
● Monitor echo: yes
● Suppress echo: yes
● Monitor: yes
● Segmentation: yes
In this mode, the individual fiber-optic links are monitored by the two connected modules.
Occurrence of a disruption
If a module fails or a fiber-optic cable breaks or disturbances are detected on the optical
transmission line, the fiber-optic link between the two OLMs is interrupted (segmented). The
PROFIBUS network is separated into two (sub)networks each remaining functional on its
own.
The problem is signaled as follows:
● The channel LEDs change to red.
● The signaling contacts of the two OLMs connected to the disturbed fiber-optic link are
activated.
Eliminating a disruption
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.
Note
If a problem occurs in networks with several active bus nodes, two logical token rings are
formed. As a result, temporary network disturbances may occur due to double tokens or
frame collisions when the full network is restored.
Note
If modules with two optical channels are used at the end of a line, the unused optical channel
must be set to the mode "bus without fiber-optic link monitoring", so that it does not cause a
broken fiber-optic cable signal, see section "Setting the mode of the electrical channel (CH1)
(Page 23)" or "Setting the mode of the electrical channel (CH0) (Page 24)".
Optical link module
Operating Instructions, 01/2020, C79000-G8976-C270-06
Planning/configuring
7.1 Network topologies
55