IEC 62148-6:2020 is available as IEC 62148-6:2020 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 62148-6:2020 covers the physical interface specification of optical transceivers for asynchronous transfer mode-passive optical network (ATM-PON) systems recommended by the International Telecommunication Union (ITU) as ITU Recommendation G.983.1. This second edition cancels and replaces the first edition published in 2003, and constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - inconsistency of types in Clause 4 has been resolved; - part and titles list in the Foreword has been deleted; - references have been updated.