Recommendation ITU-T G.984.3 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. This Recommendation includes the specifications of the following: o gigabit PON transmission convergence (GTC) layer framing; o upstream time division multiple access mechanism; o physical layer OAM messaging channel; o principles and signalling mechanism of the upstream dynamic bandwidth assignment; o ONU activation method; o forward error correction; o 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.