User's Manual

Gigabit “twister” and SONET “twister” 13
Link Loss Carry Forward (LLCF)
The fiber-to-fiber “twister” units incorporate LLCF functionality to assist in trouble-
shooting a remote connection. When LLCF is enabled
*
, the ports do not transmit link
signals until they receive link signals from the opposite port. When a lost link signal
is returned to an unmanaged “twister” unit, that lost link must then be carried
forward to a managed device (switch/hub) for trap generation. LLCF works in
conjunction with LLR.
The diagram below shows a typical network configuration with good link status
using two fiber-to-fiber “twister” units for remote connectivity. Note that LLCF is
enabled as indicated in the diagram.
Management
Station
Management
Station
Switch/Hub
w/SNMP
Switch/Hub
w/SNMP“twister”“twister”
LED lit = established link LED unlit = no link
Remote
Cable
LLCF is ON LLCF is ON
Link Loss Carried Forward Link Loss Carried Forward
LED lit = established link LED unlit = no link
Management
Station
Management
Station
Switch/Hub
w/SNMP
Switch/Hub
w/SNMP“twister”“twister”
Broken
Remote
Cable
LLCF is ONLLCF is ON
Link Loss Carried Forward
LED lit = established link LED unlit = no link
Management
Station
Management
Station
Switch/Hub
w/SNMP
Switch/Hub
w/SNMP“twister”“twister”
Broken
Cable
Remote
Cable
LLCF is ON
LLCF is ON
If a connection breaks, the “twister” units will carry that link loss forward to the
switch/hub which generates a trap to the management station. The administrator can
then determine the source of the problem.
*Units are shipped with LLCF disabled (DOWN). On the fiber-to-fiber converters (2151-AD-, 2125-xx- and 2135-34-01), LLCF is
always enabled and cannot be disabled.