in fact it happens all the time

Not generally in Big Internets, although I'd love to know anyone who has been playing with feeding congestion info into their IGPs or whatever, just out of curiosity. Moreover, even where it does happen now, it happens in the middle on a hop-by-hop basis, and not on an end-to-end basis. The latter course introduces all sorts of really interesting problems into something that I thought was nuked as a bad idea a long time ago... Sean. P.S.: I seem to have misplaced my copy of Radia Perlman's _Bridges and Routers_. Does anyone have the ISBN handy?