The OptiXtrans E6600 and OptiX OSN 1800 series use a hierarchical system architecture divided into three layers: L0 (optical layer), L1 (multiplexing layer), and L2 (service layer). According to HCIP-Transmission documentation, the E6608T/E6616 and OptiX OSN 1800 II TP/OSN 1800 V Pro models implement the L0+L1+L2 architecture, providing comprehensive functionality across optical signal management, multiplexing, and client service handling. This architecture enables scalable, flexible, and efficient transmission systems supporting various services and network demands. Other options mention partial model sets or incorrect combinations, making option B the accurate statement reflecting the system architecture.