"Is Cisco 3550 using a WS-G5486 Gigabit module? What's SFP module would you use to connect a Cisco WS-C3750X-48P-L PoE switch ? Does anyone have experience with SX to LX adapters and if they are reliable?"

A:Hi, to connect them well, you would need to use a GLC-LH-SMD transceiver for this, and a LC-SC single-mode patch cord (if they're being connected directly without an intermediate patch-panel).