Link Loss Return (LLR)
The fiber ports on the “twister” have been designed with Link Loss Return function- ality for troubleshooting remote connections. When LLR is enabled*, the port’s transmitter (TX) shuts down if its receiver (RX) fails to detect a valid receive link. LLR should only be enabled on one end of a cable and is typically enabled on either the unmanaged or remote device. LLR works in conjunction with LLCF and CLCF.
The diagram below shows a typical network configuration with good link status using two “twister” units for remote connectivity. Note that LLR and LLCF are enabled as indicated in the diagram.
Management Switch/Hub | “twister” | “twister” | Switch/Hub | Remote | |
Station | w/SNMP | A | B | w/SNMP | Station |
LLCF is ON LLR2 is ON LLR1 is OFF
LLCF is ON LLR2 is ON LLR1 is OFF
| Remote |
| Port 2 Port 1 Cable Port 2 Port 1 |
LED lit = established link | LED unlit = no link |
Example: If one of the optical conductors breaks (as shown in the diagram box below), “twister” B, with LLR2 enabled, will return a
Management | Switch/Hub | “twister” |
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| w/SNMP | A |
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| LLCF is ON |
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| LLR2 is ON |
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| LLR1 is OFF |
| Broken | LLR1 is OFF |
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| Port 2 | Conductor | Port 1 |
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| Link Loss Carried Forward |
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| Link Loss Returned |
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| LED lit = established link | LED unlit = no link |
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IMPORTANT: LLR must not be active on both ends of a configuration. If it is, the link can never be established.
*Units are shipped with LLR disabled (OFF). On the
12 User Guide
