METRObility Optical Systems 2152-A7-01, 2152-AY-01, 2152-77-01 manual Link Loss Carry Forward Llcf

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 Switch/Hub				Switch/Hub Management
Station	w/SNMP	“twister”	“twister”	w/SNMP	Station
		LLCF is ON	LLCF is ON
			Remote
			Cable
LED lit = established link		LED unlit = no link

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.

Management Switch/Hub				Switch/Hub Management
Station	w/SNMP	“twister”	“twister”	w/SNMP	Station
		LLCF is ON	LLCF is ON
		Broken
		Remote
		Cable
	Link Loss Carried Forward		Link Loss Carried Forward
LED lit = established link		LED unlit = no link

Management Switch/Hub				Switch/Hub Management
Station	w/SNMP	“twister”	“twister”	w/SNMP	Station
		LLCF is ON	LLCF is ON
		Remote		Broken
		Cable		Cable
	Link Loss Carried Forward
LED lit = established link		LED unlit = no link

*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.

Gigabit “twister” and SONET “twister” 13