Summary The present Recommendation describes the Transmission Convergence Layer for Gigabit-capable Passive Optical Networks - a family of flexible access networks capable of providing a range of broadband and narrow-band services, operating at the rates of 2.48832 Gbit/s downstream, and 1.24416 or 2.48832 Gbit/s upstream. The Recommendation includes the specifications of the following: " Gigabit PON Transmission Convergence (GTC) layer framing; " Upstream Time-Division Multiple Access mechanism; " Physical layer OAM messaging channel; " Principles and signalling mechanism of the Upstream Dynamic Bandwidth Assignment; " ONU activation method; " Forward Error Correction; " Security. This Recommendation forms an integral part of the G.984 series of ITU-T Recommendations that, together, specify a single coherent set of access transmission systems.