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: • gigabit PON transmission convergence (GTC) layer framing; • upstream time division multiple access mechanism; • physical layer operation, administration and maintenance (OAM) messaging channel; • principles and signalling mechanism of the upstream dynamic bandwidth assignment; • optical network unit (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. Amendment 1 provides necessary extensions to support Class D ODN. Amendment 2 implements the TC layer consistency updates across the ITU-T PON specifications including Deactivation Reason Codes and Forgotten ONU timer.