Thank you all. Even though a lot of uncertainty remains [?] these comments have been very helpful.
@re0 - that helps me understand. I’ve seen this iirc, a current rate going above the attainable, and your opinion sounds just right, helping me understand such a confusing and surprising observation.
I realise that I should have asked ‘when does the attainable rate figure change?’ in your experience. I ought to check mine, I just assumed that what I see is set at sync time, dsl connection establishment time, and does not change after that until the next resync. I don’t know why I assumed that and I don’t know whether or not it’s true. Is that right? Or does it change dynamically during the lifetime if the connection?
@aesmith - could be, thanks for that. Those figures are similar to mine relatively. For example I might see 3100 kbps sync rate downstream and an attainable of 3400 kbps, a figure which despite the name is completely unattainable.
That’s why they call it ‘attainable’, because it’s completely impossible. (Unless perhaps that’s at 0dB SNRM, but how long would that last, so what’s the point?)
@ejs - very helpful, the insight about min INP requirement being part of the key to understanding the definition of ‘attainable’ rate. And there’s also the part about artificial limits, ‘caps’, being ignited too. I don’t think that would help me understand in my own particular case of course. Not that that challenges this opinion about the contributors to the definition of attainable.
In my case my real sync rates are not some magic round number, some low integer x times some integer multiple of a power of ten say.