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 supports indoor and outdoor communications over low-voltage lines@ medium-voltage lines@ through transformer low-voltage to medium-voltage and through transformer medium-voltage to lowvoltage power lines in both urban and long distance rural communications. This Recommendation addresses grid to utility meter applications@ advanced metering infrastructure (AMI)@ and other 'Smart Grid' applications such as the charging of electric vehicles@ home automation and home area networking (HAN) communications scenarios. This Recommendation does not contain the control parameters that determine spectral content@ power spectral density (PSD) mask requirements and the set of tools to support a reduction of the transmit PSD; all of which are detailed in Recommendation ITU-T G.9901.