Automatic bidirectional OTDR scan

Automatic OTDR scan triggering events

The OTDR scan, starts automatically when events like span fault, span restoration, automatic OTDR scan enabling, device power cycling, and line card cold reload occur.

Autoscan direction and duration

The OTDR autoscan scans events in both Tx and Rx directions.

In both span up and span down events, the bidirectional OTDR scan process terminates after both Rx and Tx scans have been completed successfully. You can stop the scan sequence by disabling the autoscan feature.

The autoscan duration for Auto and Expert modes, the scan takes upto three minutes to complete. . During the autoscan, the OTDR-SCAN-IN-PROGRESS-RX and OTDR-SCAN-IN-PROGRESS-TX alarms are raised and get cleared once the scan is finished.

Autoscan behavior

The autoscan has these key behaviors:

• The autoscan reserves the span on the peer node and locks the OTDR resource to prevent manual triggering of a scan using the otdr-start command . However, if a manual scan is already in progress, the autoscan will wait until the manual scan is completed before proceeding.

• The autoscan terminates the ongoing scan and starts a new one if a change in Span Status is detected.

Span fault and restoration events detection

This table details how the span fault and span restore events are detected:

Unidirectional and bidirectional fiber cuts

The bidirectional OTDR auto scan functions in the event of unidirectional and bidirectional fiber cuts, and during fiber restoration events.

In a span including both broken and non-broken fibers, the scanning behavior differs based on the type of fiber cut:

• Unidirectional Fiber Cut:

  • The broken fiber is scanned in both the Rx and Tx directions by the Near End (NE) and Far End (FE) nodes.

  • The non-broken fiber is scanned only in the Tx direction.

• Bidirectional Fiber Cut:

  • Both fibers are scanned in both the Rx and Tx directions.

Span down event

For a bidirectional autoscan triggered by a span down event:

• Timeslots are used for both unidirectional and bidirectional fiber cuts as the node communication and hence negotiation is not possible.

• Timeslots are of equal duration and are alternately assigned to Rx and Tx directions. This order is consistent across both NE and FE node.

• If a scan cannot be completed inside the assigned timeslot or the scan execution failed for any reason, the execution is rescheduled at the next available timeslot for that port/direction.

Span up event

For a bidirectional autoscan triggered by a span up event:

• Rx and Tx scans are executed sequentially through negotiation with the remote node, eliminating the need for time slots.

  The OSC and associated Ethernet communication must be functioning properly to initiate the scan.

In both span up and span down events, the bidirectional OTDR scan process terminates after both Rx and Tx scans have been completed successfully. You can stop the scan sequence by disabling the autoscan feature.