Recommendation ITU T G.9903 contains the physical layer (PHY) and data link layer (DLL) specifications for the G3-PLC narrowband orthogonal frequency division multiplexing (OFDM) power line communication transceivers for communications over power lines over frequencies below 500 kHz. G.9903 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. Amendment 1 to Recommendation ITU-T G.9903 (2014) adds support for coexistence with other narrowband PLC technologies via the preamble based coexistence mechanism specified in IEEE 1901.2 Clause 10.