"This Recommendation concerns GPON systems with optical link budgets up to the logical limits of the transmission convergence (TC) layer. The increased optical capability@ which includes both increased overall fibre length and increased overall splitting ratio@ is referred to in this Recommendation as ""reach extension"". The primary concerns addressed are the increase of the loss budget and the management of optical impairments. This Recommendation considers mid-span extension@ which uses an active extension node placed in the middle of the optical network. The recommended parameters for the ODN(s) involved in this scheme are specified. Single-sided extension is considered as an improvement to the OLT interface@ and is described in [ITU-T G.984.2] as amended. The systems considered here must remain compatible with existing ONTs. Furthermore@ the approaches should maintain compatibility with existing OLTs to the maximum extent possible. It is recognized that some modification of the OLT equipment may be necessary@ but this should be minimized. Two system architectures are considered: optical amplification@ and opto-electronic regeneration. These can be viewed as providing reach extension at the physical layer. The key interfaces and functional blocks in each of these architectures are identified and specified."