Thanks for you both replies.
"MAC address learning priority of user-side ports higher than that of network-side ports, MAC address will be duplicate"
is it really true? It is different from what some consultant told me before. Below is what he told me.
when OLT in dual homing protection mode, some guy told me the mac address learning priority of network side is higher than user-side, then need to configure layer port isolation on upstream switch (core switch), otherwise, need to wait for 5 minutes when OLT failover.,
Is it correct when OLT failover? Please advise, thanks.