what is the meaning of S-16.1 defining an interface?

In SDH, what is the meaning of S-16.1 defining an interface?

A.
S-16forSTM-16, 1 for Short Haul

B.
S for Short Haul, 16forSTM-16,1 for 1-port card

C.
S for Short Haul, 16forSTM-16,1 for 1310 nm

D.
S for Short Haul, 16forSTM-16,1 for 1st port on card