I understand now, CASR is a TalkTalk-specific thing. Is BBEUnnnnnnn a BT-specific thing and is it similar ? I see BBEU numbers reported to me by AA in a PPPoEoA or PPP connect acknowledgment message. Not sure of the protocol association details. I posted about this last year somewhere.
AA now, thank god, sends you this BBEU plus an upstream IP PDU rate, and current up- and downstream sync rates for the link. A Firebrick can now use this to calculate the right egress rate or upstream PPP bitrate from the upstream sync rate each time you PPP-connect. Before, in the bad old days, you had to guess an upstream rate and specify it in the Firebrick’s XML config, and the number was never up to date as the sync rate upstream could vary.