Supplement 63 to ITU-T G-series Recommendations describes how a flexible ITU‑T G.989.3 transmission convergence (TC) layer implementation can be used to support an ITU‑T G.987.3 or ITU‑T G.9807.1 passive optical network (PON).

ITU‑T G.989.3 was largely derived from ITU-T G.987.3. The ITU-T G.9807.1 Appendix C TC layer specification was derived from ITU-T G.989.3, with ITU-T G.9807.1 Appendix II describing this derivation in detail. ITU‑T G.9807.1 also specifies that an ITU-T G.9807.1 compliant optical line terminal (OLT) will interwork with an ITU‑T G.987.3 compliant optical network terminal (ONT).

It should be evident from this chain of derivation that a flexible TC layer implementation that supports ITU‑T G.989.3 can support an ITU-T G.9807.1 or ITU-T G.987.3 operation. This Supplement describes the implementation flexibility required.