Annex A uses the frequency range from 25 kHz to 138 kHz for the upstream (138-2.2GHz for the downstream).
Annex B uses the frequency range of 138 kHz and 276 kHz for the upstream (276-2.2GHz for the downstream). The bandwidth for Annex B is therefore less for the downstream.
Annex A can only be used for analogue telephone connections, Annex B can be used for analogue as well as digital (ISDN).
In Switzerland, Annex A is used for analogue, Annex B for ISDN. In Germany, ONLY Annex B exists.
So the D firmware will only support Annex B, which is not used in Switzerland today (because we now have IP telephony and therefore use the larger bandwidth).
I hope this helps to clarify the use of Annex A and B. You can find more detailed information at
https://de.wikipedia.org/wiki...