Which one of the following protection schemes can provide OLT-level protection?

OLT-level (device-level) protection is achieved by dual-homing ONUs to two independent OLT interfaces so that services can switch to another OLT when one fails. In Huawei protection taxonomy, the dual-homing scheme (as contrasted with single-homing) provides device-side redundancy for the OLT. By comparison, Ethernet port protection groups and LACP protect uplink links and bandwidth at Layer 2, not the OLT device itself; single-homing does not protect against OLT failure.