Planet FST-802S15 [14/17] Link loss return llr

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4.2 Link Loss Return (LLR)

The fiber ports of FST-80X have been designed with an LLR function for troubleshooting a remote connection. LLR works

in conjunction with LLCF.

When LLR is enabled*, the port’s transmitter shuts down when its receiver fails to detect a valid receive link. LLR should

only be enabled on one end of the link and is typically enabled on either the unmanaged or remote device.

The diagram below shows a typical network configuration with a good link status using FST-80X for remote connectivity.

Note that LLR and LLCF are enabled as indicated in the diagram.

Management Switch/Hub Media Media Switch/Hub Management

Station w/SNMP Converter Converter w/SNMP Station

● LED lit = established link ○ LED unlit = no link

LLCF is ON

Fiber

Cable

If one of the optical conductors is bad (as shown in the diagram box below), the converter with LLR enabled will return a

no-link condition to its link partner. With LLCF also enabled, the no-link condition is carried forward to the switch/hub where

a trap is generated to the management station, and the administrator can then determine the source of the loss.

Management Switch/Hub Media Media Switch/Hub Management

Station w/SNMP Converter Converter w/SNMP Station

● LED lit = established link ○ LED unlit = no link

LLCF is ON

Port 2

Broken

Fibe

Port 1

Link Loss Carried Forward Link Loss Carried Forward

Link Loss Returned

Notice:

1: LLR must NOT be active on both ends of a configuration. If it is, the link can never be established.

2. Units are shipped with the LLR function disabled (DOWN).