METRObility Optical Systems R125-34, R135-34, R125-37 manual Link Loss Return LLR, Sonet

Link Loss Return (LLR)

Both ports on the Radiance SONET single interface line card have been de- signed with LLR for troubleshooting a remote connection. When LLR is enabled*, the port’s transmitter shuts down if its receiver 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 with in conjunc- tion with Link Loss Carry Forward.

The diagram below shows a typical network configuration with good link status using two SONET line cards for remote connectivity. Note that LLR is enabled as indicated in the diagram.

Management Switch/Hub			SONET		SONET	Switch/Hub	Remote
Station	w/SNMP	Line Card A			Line Card B	w/SNMP	Station
			LLR2 is ON		LLR2 is ON
			LLR1 is OFF		LLR1 is OFF
			Port 2 Port 1	Remote
				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), Line Card B, with LLR2 enabled, will return a no-link condition to its link partner, Line Card A. Because the line cards are designed with LLCF functionality, the no-link condition is carried forward to the switch/hub where a trap is generated to the management station. The network administrator can then determine the source of the loss.

Management	Switch/Hub	SONET			SONET	Switch/Hub	Remote
Station	w/SNMP	Line Card A		Line Card B		w/SNMP	Station
		LLR2 is ON			LLR2 is ON
		LLR1 is OFF			LLR1 is OFF
				Broken
		Port 2	Conductor		Port 1
Link Loss Carried Forward					Link Loss Carried Forward
			Link Loss Returned
LED lit = established link			LED unlit = no link

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 the LLR function disabled (DOWN).

10 User Guide