Two SFP (1.25G) module kit, 20Km, single mode - S-35LC20D is a 1.25G Single Mode optical SFP module with a LC connector, T1310nm/R1550nm, which works for connections up to 20km and supports DDM. The S-53LC20D is a 1.25G Single Mode optical SFP transeiver with an LC connector,T1550nm/R1310nm, which works for connections up to 20km and supports DDM