What is the Fibroptico FO-GLC-5531DD-20KM?
The Fibroptico FO-GLC-5531DD-20KM is a SFP optical transceiver module, listed by the manufacturer as "FO-GLC-5531DD-20KM 1000BASE-BX BI-DIRECTIONAL SFP TRANSCEIVER; 1550 TX/1310 RX". It is part of Circular Telecom's surplus and refurbished telecom/IT equipment inventory.