Dear friend!
Please refer to the following information:

| 1. Interface board area | 2. Fan area |
| 3. Processing board area | 4. Cable routing area |
Interface board area: This area houses the interface boards of the OptiX OSN 3500.
Fan area: This area houses three fan modules, which dissipate heat generated by the equipment.
Processing board area: This area houses the processing boards of the OptiX OSN 3500.
Cable routing area: This area houses fiber jumpers in a subrack.
Slot Description:

The slots in an OptiX OSN 3500 subrack are allocated as follows:
Slots for service interface boards: slots 19-26 and 29-36
Slots for service processing boards: slots 1-8 and 11-17
Slots for cross-connect and timing boards: slots 9-10
Slots for system control and communication boards: slots 17-18 (slot 17 can also house a processing board)
Slots for power interface boards: slots 27-28
Slot for an auxiliary interface board: slot 37
Slots for fan boards: slots 38-40
More: Hardware Description
Thank you!