Optical modules whose models have the SS letters are single-fiber SFP modules,
such as the USFP-03/SS35-D-R. These SFP optical modules must be used in pair,
which means that the Tx wavelength of the sender SFP optical module must be
consistent with the Tx wavelength of the receiver SFP optical module, and vice versa.
For example, the USFP-03/SS13-D-R and USFP-03/SS15-D-R should work together.