Right, I'm not sure I follow the siginficance of bearer 0 /1. Does that meant there is only interleave on retransmission as a part of G.INP so there is not really an effective delay on my line at all times?
Look at the "AgR" figures for the two bearers - that is the "Aggregate Rate" of each, in kbps. That's 80,614 kbps on bearer 0 and 95kbps on bearer 1.
The VDSL2 specifications allow data to be transferred across a number of "bearer channels" between the two modems. However, the G.INP specs narrows things down to a few options.
In BT's implementation, they choose to put the user data into bearer 0, alongside some of the control and framing data - so it aggregates to a rate of 80.6Mbps. Bearer 0 then has retransmission configured (INP=48, in your case), but with delay=0. However, the modems configure a very small amount of FEC and interleaving in this bearer, and my calculations suggest you see latency of about 0.2ms in your user data (ie the stuff your router passes).
There are only a few of the modem control bits allocated to bearer 1, so it only takes 95kbps. However, the modems obviously think it better to be correct than fast with these control bits, as it uses the old-style FEC and interleaving settings for these (100% FEC overhead and 4ms latency). But none of this data is part of the data seen by your router, even when re-transmission happens.
So, delay would be about 0.2ms as standard, When G.INP is retransmitting a lot, any packets that require retransmission may take up to 5ms. See
this thread for an example.
