Link Loss Return (LLR)
The fiber optic ports of the access line cards have been designed with an LLR function* for troubleshooting a remote connection.
When LLR is enabled, the fiber port’s transmitter shuts down if 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 access line cards for remote connectivity.
| Switch/Hub | Access | Access | Customer |
PC | w/SNMP | Line Card | Line Card | Site |
|
| LLR is OFF | LLR is ON |
|
|
|
| Fiber |
|
|
|
| Cable |
|
LED lit = established link | LED unlit = no link |
| ||
If one of the optical conductors is bad (as shown in the diagram box below), the card 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.
| Switch/Hub | Access | Access | Customer |
PC | w/SNMP | Line Card | Line Card | Site |
|
| LLR is OFF | LLR is ON |
|
|
|
| Broken |
|
|
|
| Fiber |
|
|
|
| Conductor |
|
|
| 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).
18 User Guide