Media converters work on the physical layer of the network.
They receive data signals from one media and convert them to another
device. They make one cable "look" like another cable without changing
the nature of the network.
In its simplest form, a media converter is a small device with
two media-dependent interfaces and a power supply. It can be installed
almost anywhere in a network. The style of connector depends on
the selection of media to be converted by the unit. In a Fast Ethernet
environment, a 100Base-TX to 100Base-FX Media Converter connects
a 100Base-TX twisted-pair device to a 100Base-FX compliant single
or multimode fiber port that has a fiber-optic connector. In a Gigabit
Ethernet, a media converter commonly is deployed to convert multimode
to single-mode fiber or vice versa.