A receptacle connector for mating with a plug connector, the receptacle connector includes: a terminal module comprising an insulative housing, two rows of terminals, and a metallic shielding plate, the insulative housing having a base portion and a tongue portion, the tongue portion defining two opposite surfaces, the two rows of terminals being reversely-symmetrically arranged at the two surfaces of the tongue portion, the metallic shielding plate located between the two rows of terminals; and a shielding shell retained to the insulative housing and forming a mating cavity to receive the tongue portion, wherein the shielding shell defines a mating protrusion on one of the plurality of side walls, the mating protrusion extending outwardly to be precluded from reversely mating with the plug connector which has a contour compliant with said mating cavity and an identification protrusion accommodated in the mating protrusion.