Recommendation ITU‑T G.9903 contains the physical layer (PHY) and data link layer (DLL) specification for the G3‑PLC narrowband orthogonal frequency division multiplexing (OFDM) power line communication transceivers for communications via alternating current and direct current electric power lines over frequencies below 500 kHz.

This Recommendation uses material from Recommendations ITU-T G.9955 and ITU‑T G.9956; specifically from Annexes A and D of ITU-T G.9955 and Annex A of ITU-T G.9956. New technical material has not been introduced in this version.

The control parameters that determine spectral content, power spectral density (PSD) mask requirements and the set of tools to support the reduction of the transmit PSD can be found in Recommendation ITU-T G.9901.

This consolidated text integrates the following changes:

the support for an optional coherent mode for use in CENELEC bandplans;

support for a new bandplan in CENELEC B;

a regional annex for Japan (Annex F);

a new routing algorithm (LOADng) that replaces the old one (LOAD);

a clause on coexistence with other NB-PLC technologies;

various clarifications and corrections including on header compression, and channel access mechanism;

the removal of contention free access (CFA); and

a major editorial restructuring.