User`s guide

User’s Guide 15
Link Loss Return (LLR)
The fiber optic ports of the Metrobility AutoTwister have been designed
with LLR
*
functionality for troubleshooting a remote connection.
When LLR is enabled, the fiber port’s transmitter shuts down when its
receiver fails to detect a valid receive link. LLR is normally enabled on
one end of the link and is typically enabled on either the unmanaged or
remote device. Setting LLR on both ends of the link necessitates auto-
recovery. See Auto-Recovery on page 17.
The diagram below shows a typical network configuration with good link
status using AutoTwisters for remote connectivity.
If one of the optical conductors is bad (as shown in the diagram box
below), the AutoTwister with LLR enabled will return a no-link condition to
its link partner. This aids the network administrator in determining the
source of the loss.
PC
Remote
Station
Switch/Hub
w/SNMP
Switch/Hub
w/SNMP
AutoTwister AutoTwister
TP TPFiber
Cable
LED lit = established link LED unlit = no link
LLR is OFF
LLR is ON
PC
Remote
Station
Switch/Hub
w/SNMP
Switch/Hub
w/SNMP
AutoTwister AutoTwister
Link Loss Returned
LED lit = established link LED unlit = no link
TP TPBroken
Fiber
Conductor
LLR is OFF LLR is ON
*Units are shipped with the LLR function disabled (OFF).