Recommendation ITU-T G.987.4 outlines the architecture and interface parameters for 10 Gigabit-capable passive optical network (XG-PON) systems with extended reach using a physical layer reach extension device, such as a regenerator or optical amplifier in the fibre link between the optical line termination (OLT) and optical network unit (ONU). Wavelength converting, continuous mode, 1:N and combination type reach extenders are also described. The maximum reach is up to 60 km with loss budgets of in excess of 28.5 dB being achievable in both spans.