TD Alarms Falsely Reported by Some Boards Using Pluggable Optical Modules in WDM Products

 

Keywords: WDM products, OptiX OSN 8800

Summary:

If no intra-board cross-connection from the WDM side to the client side is configured for

boards that support intra-board cross-connections, these boards may falsely report TD

alarms when their optical port lasers are turned on.

[Problem Description]

Trigger conditions:

The problem occurs on a board when the following conditions are present:

The board is listed in the table above. No intra-board cross-connection shown in Figure 1

is configured on the board. Specifically, no unidirectional cross-connection from the WDM

side to the client side is configured on the board.

Figure 1 Intra-board cross-connection

 

WDM side

WDM side

Pluggable optical modules are used on the board and the optical port lasers are turned on.

Symptom:

TD alarms are reported.

Identification method:

The problem occurs if the trigger conditions and symptom are satisfied.

[Root Cause]

When no intra-board cross-connection shown in Figure 1 is configured on the board, the module

bias current increases. In addition, the laser transmit efficiency decreases when the ambient temperature

increases. To maintain stable module power, the bias current further increases. When the bias current

increases to a value greater than the alarm threshold, TD alarms are reported. The laser transmit efficiency

varies according to modules. Therefore, not all modules have this problem.

[Impact and Risk]

The board falsely reports TD alarms. Consequently, operators may consider that the optical modules are faulty.

[Measures and Solutions]

Recovery measures:

Take either of the following measures:

Turn off the lasers after confirming that no service is deployed.

Configure intra-board cross-connections for the related optical ports.

Workarounds:

Turn on the lasers after configuring intra-board cross-connections.

Preventive measures:

Update the related product manuals. Specifically, add descriptions in the product manuals that intra-board

cross-connections shown in Figure 1 must be configured for the boards listed in the table above if the lasers on

these boards are turned on to test light emitting.

 

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