What is the difference between multimode and singlemode fibre?
Multimode fibre has a relatively large light carrying channel, usually 50 or 62.5 microns in diameter. It is commonly used for short distance transmissions with LED based optical fibre equipment, and has limitations in regards to bandwidth capacity and distance.
The typical distance limitation of a 100Mbps 50/125µm multimode (MM) fibre is 5km.This reduces to 550m for Gigabit.
Singlemode fibre has a smaller light carrying channel of 8 to 10 microns in diameter. It is used for large bandwidth transmissions over longer distance, and uses laser diode based optical fibre transmission equipment.
Standard 9/125µm multimode (SM) fibre can provide a distance of 25km at 100Mbps. Again, this reduces for Gigabit. Using readily available industrial equipment, distances up to 120km are possible. Longer distances would generally require more specialised ($) equipment.