Please who knows the difference in the different models of the 3550 switches (i.e. Cisco Catalyst 3550 24 DC SMI Switch, Cisco Catalyst 3550 24 EMI Switch, Cisco Catalyst 3550 24 FX SMI Switch, Cisco Catalyst 3550 24 PWR Switch, Cisco Catalyst 3550 24 SMI Switch). And what is Advanced IP Routing on these swtiches?. Is that support for routing protocols.