Hello,
1. check FTP account on OLT, it was not set, so I set it to be similar to that on U2000.
FTP must be set on OLT as it will download XML file from U2000 then configure ONT through OMCI.
2. Checking SNMP parameters on OLT, found trap port set to 161, it should be set to 162.
Traps must be configured correctly as OLT will report to U2000 the status of XML file transfer.
Test again, problem solved and VAS can be configured.
Thanks