TR-069, I presume.
Yes, that all makes sense.
I very much doubt that the Linux kernel installed on the device is receiving any support. I suspect it was a case of build the kernel, install it into the image and forget about it!
With your ISP's usage of TR-069, I suspect any manual intervention may delete the configuration and the ROM-D partition.
Yes, in view of what you have explained, above. However if someone has one of those devices and is not tied to any particular ISP, then clearing the ROM-D partition would be step number two on the list of: "How to Revert Back to a Vanilla ZyXEL Device". (Step one would be obtain the supervisor password.)
That pdf about TR-069 is some serious reading but it;s good to see what kind of tricks they can perform.
I think that in this ips's case LTS stands for very slow service, it takes about 1 week to get a reply...
Frustrated by the slow ips and my Voip problems I decided to give it a try.
Spend the last 2 days flashing and manually "re-constructing" the configuration.
But eventually I got there !
Right now I am on 1.00(AAKL.28)C0.
I started with .7 with the idea I would hopefully be able to upload the "clean" backups that I created earlier, since ROM-D would likely be erased.
Well ROM-D got erased and my configs were not valid, some illegal entries.
So I ended up manually configuring the modem with the notes that I made.
Once sorted out I saved that configuration.
After that I upgraded in small increments, each time restoring config from previous fw backup and create new "upgraded" config.
The config files created seem the load just fine.
Even the supervisor password somehow survived.
Right now I feel like minced meat, but so far it seems to pay off, internet working and hopefully Voip problems solved.
lets hope it will stay that way.
Later when my head is fresh I might have another look at these old configs and see if I can find those illegal entries.
Thanks again for your help !