In order to achieve consistent and compatible fibre systems, it is recommended that the convention defined in ISO / IEC 11801 is used where channel A (right) is the input and channel B (left) is the output.
Extract from ISO / IEC 11801 Fibre patch cord termination configuration:
‘It is recommended that connection of patch cords and equipment cords to the duplex adapter be made by means of a duplex connector assembly. Optical fibre patch cords, whether they are used for cross connection or interconnection to equipment, shall be of a crossover orientation such that position A goes to position B on one optical fibre, and position B goes to position A on the other optical fibre of the optical fibre pair.’
‘Each end of the fibre patchcord shall be identified to indicate position A and position B if the components can be separated into its simplex components. For alternate connector designs utilising latches, the latch defines the positioning in the same manner as the keys. For simplex connectors, the connector that plugs into the receiver shall be considered position A, and the connector that plugs into the transmitter shall be considered position B.’