Siemens SIMATIC NET Operating Instructions Manual page 62

Planning/configuring
7.1 Network topologies
How the LEDs react in the redundant optical ring
A frame received by any channel is passed on to all other channels. If the frame was
received on an optical channel, it will also be sent back to the sender on the same channel
as an echo and therefore serves as a monitoring frame to test the fiber-optic link between
the OLMs.
The OLM recognizes whether a received frame is an echo or a frame that was forwarded. In
the case of an echo frame, the channel LED stays off, whereas in the case of a forwarded
frame it will light up yellow. In networks with more than two OLMs, echo frames and
forwarded frames will alternate quickly. Due to the extended display-time of at least 300 ms,
all channel LEDs are lit yellow continuously.
The channel LEDs may react differently in the redundant optical ring only if the following
conditions are met:
1. The redundant optical ring consists of exactly two OLMs and the two fiber-optic links are of different
length (difference > approx. 2 m).
Under these conditions, the receiving OLM will always receive a sent frame first on the
channel with the shorter fiber-optic link. This channel signals this with a lit yellow channel
LED. The frame on the other optical channel is interpreted as an "echo frame", the channel
LED stays unlit. Since the fiber-optic cable lengths represent static variables, the display
reaction is also static.
Configuration 1 (FOC1 < FOC2) , LED display:
1. Situation, no FO cable interruption:
System LED
CH1/0 LED
CH2 LED
CH3 LED
2. Problem, FOC1 interrupted:
System LED
CH1/0 LED
CH2 LED
CH3 LED
3. Problem, FOC2 interrupted
System LED
CH1/0 LED
CH2 LED
CH3 LED
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OLM 1
Lit green
Lit yellow
Lit yellow
Not lit
OLM 1
Lit green
Lit yellow
Lit red
Lit yellow
OLM 1
Lit green
Lit yellow
Lit yellow
Lit red
Operating Instructions, 01/2020, C79000-G8976-C270-06
OLM 2
Lit green
Lit yellow
Not lit
Lit yellow
OLM 2
Lit green
Lit yellow
Lit yellow
Lit red
OLM 2
Lit green
Lit yellow
Lit red
Lit yellow
Optical link module