becasue OLT provious version doesn't support IPv6, need to upgrade the intermediate version and then upgrade the latest versioin. if OLT already supports IPv6, upgrade the latest version directly.

upgrade steps:

1. if OLT current version is less than V2.03.57R, please upgrade to V2.03.57R first.
  (1)uncompress the file V1600D_V2.03.57R.rar, upgrade V1600D_UBI_V2.03.57R.ubi and reboot OLT. then upgrade V1600D_IMG_V2.03.57R.img and reboot OLT again.
  (2)ugprade V1600D_V2.03.57R_IPv6_ALLinONE.ubi and reboot OLT.

2. if OLT current version is or over V2.03.57R, please upgrade V1600D_V2.03.57R_IPv6_ALLinONE.ubi. then reboot OLT again.

3. after upgraded to V2.03.57R, please upgrade the latest version.(after upgraded both files ubi and img, reboot OLT)