MDA is a module that can be inserted into a modular Ethernet switch to provide connectivity between different media types. Modular Ethernet switches typically have two to four media-dependent adapter (MDA) slots on the front panel, where you can easily insert and remove MDAs for providing various media connectivity configurations.
Graphic M-7. Media-dependent adapter (MDA).
By selecting and inserting different MDAs into a modular switch, you can quickly reconfigure complex Ethernet networks. Bridging between the different types of media is performed internally by the chassis circuitry inside the switch.