Recommendation ITU-T G.9991 specifies the system architecture, physical (PHY) layer and data link layer (DLL) for high-speed indoor optical wireless communication transceiver using visible light. Amendment 1 includes updates on security to accept IEEE 802.1X-based authentication and alignment with G.9960/G.9961 Recommendations. Corrigendum 1 includes alignment to ITU-T G.9961/ITU-T G.9962 Recommendations. Amendment 2 includes a mechanism to support advanced inter-domain mobility through an external controller.