I am currently using a Billion BiPAC 7800N router.
I tried your suggested values but then found that I could neither access the User Interface, nor access the internet. Reset back to makers settings and OK.
What did not help was that there is so much scattered on different pages and I got the impression that I had lost access before I could get to the next page.
I thought that setting up a Cisco PAP2T for VoIP was a severe challenge, but the finer points of a Billion/DrayTek set-up may be an equal challenge
Andrews & Arnold FTTC
DrayTek Vigor 2920Vn
Andrews & Arnold Data SIM