I should have looked at the standard default config that the brand new ones come with, for inspiration.
Rationale: not entirely rational. [Remember I am completely full of drugs.
]
I bought one from AA ages ago when they still had some stock and that was really cheap. I specifically wanted to use the AA config, although with Burakkucat’s help I did disable the TR-069 remote updating, because as you said, I have custom firmware.
AA staff did the donkey work so that it just worked immediately out of the box in modem-only mode as I asked, as they set up the basic ADSL settings.
I also have a slightly tuned config in other respects: (1i) going on a tip from Burakkucat, I have locked it to G.992.3 only, disabling auto-mode because I do not want it to select G.992.5. This optimistic tweak is in hope of slightly higher performance by reducing the input frequency range window and so reducing the total noise ingested. That is the idea, but it does not seem to deliver any improvements from the evidence of experiments. Since it doesn't hurt, I have kept it in though. (2) I also have slightly reduced overhead by changing from RFC2684 LLC to the more efficient VC-MUX, which I can safely do because I am not on 20CN whereas AA would have to do two configurations.
I hoped I could get internet access to the modem going, behind my usual firewalling, but have not got that far. I wanted to get NTP to work and DNS and also ideally I wanted to make it really easy for AA staff to directly log in and have a peep at stats without me having to dig them out and send them to AA, cutting out the round trip. For that reason I wanted some other AA customisations such as correct IP addresses set for AA's NTP server, DNS servers etc.