My WS-C3550-48-SMI switch has a lot of fastEth ports (48) and I need to have a lot of gigEth ports. Is replacing the switch teh only option or changing the module can also be thought about? I explored a lot about it on internet/Google but no luck till now.
The 3550 is a fixed chassis switch. The modular switches in the Cisco range are the 4500 and 6500 switches so you need a replacement i'm afraid - either a 3560 or a 3750.