Ethernet has a range of about 100meters (328') over copper cable. MiniGBIC port gives you the ability to install / slide in a SFP (Small Form factor Pluggable) module.
Usually these modules can be long haul or short haul optical ethernet connections. These SFP modules can extend ethernet way beyond the 100 meter ( 328' ) copper limitation, allowing for ethernet connectivity , say between buildings or between wireing closets that are beyond 100meters. Ethernet running over fiber is not susceptible to electrical noise, which can affect ethernet running over Cat cabling.
the following link goes into too much information on the SFP modules that can fit into traditional Cisco switches. It relevant for the theory only. Check the SG102-24 guides or datasheet when ordering SFP modules for that switch.
http://www.cisco.com/en/US/products/hw/modules/ps4999/products_tech_note09186a00807a30d6.shtml
regards Dave
