This Recommendation concerns 10 Gigabit-capable passive optical network (XG-PON) 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 optical distribution network(s) ODN(s) involved in this scheme are specified. Single-sided extension is considered as an improvement to the optical line terminal (OLT) interface.

The systems considered here must remain compatible with existing optical network units (ONUs). 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.

Optionally, optical-electronic-optical (OEO) type reach extender (RE) units may support a burst mode to continuous mode (BM to CM) conversion function, as specified in clause 6.2. In this case, it is also necessary to introduce a CM to BM conversion function before the S/R interface at the OLT.

Optionally, both optical amplifier (OA) and OEO type RE units may support the wavelength conversion (WC) function, as specified in clause 6.4. In case of WC-enabled RE units, it is also necessary to introduce a WC-function block before the S/R interface.

Optionally, combination RE units may support all the functions described here in ITU-T G.987.4, and the G-PON RE functions described in [ITU-T G.984.6].

The optional support of a type-B type protection in RE units is described.