FRITZ!Box devices will ask you to select an Annex during the configuration. This setting depends on the type of your connection so you may need to adapt it in case your line gets converted from ADSL to VDSL, or vice versa.
With an ADSL subscription you should use Annex A.
As for VDSL, all recent FRITZ!OS are programmed in a way that no matter what Annex you select, the device configures itself with Annex A if the following requirements are met:
- You have chosen Belgium in Regional Setting
- Your VDSL line is connected to Broadcom DSLAM
The only situation where you absolutely need to select Annex B is when DSLAM is Ikanos and not Broadcom.
How do I know which DSLAM I am connected to?
Go to Internet on the left menu and click on DSL Information in a drop-down list. Hit Overview tab. Under DSL Central Exchange you will see whether DSLAM is Broadcom or Ikanos.
All DSLAMs at ROPs that support vectoring (so a vast majority of them) are Broadcom. If your line is connected to ROP with vectoring support, you can basically select any setting, the device will switch to Annex A anyway.