IEC 63171:2021 covers shielded and unshielded free and fixed connectors, circular or rectangular, for balanced single-pair data transmission, with current-carrying capacity.It specifies the IEC 63171 series' common mechanical, electrical and transmission characteristics and environmental requirements, as well as required test specifications.This document does not describe a specific mating interface. Detail specifications of mating interfaces complying with this document can be found in the family of detail specification standards IEC 63171-X (type X).Within their own type, the shielded and unshielded connectors are interoperable for their transmission performance and can be exchanged; though the shielded version has improved alien crosstalk and coupling attenuation properties