Discussion of ECN API?

[Bruce Barnett <dccp@grymoire.com>]

I've been involved with the application perspective of DCCP
programming, or rather - application programming aware of congestion,
and I was wondering if there exists any API for other transport
protocols that make congestion information available to the
application?  In particular, is there any existing API to extract the
ECN information that can be used for a model?  Or if it is missing, -
how should it be specified?

One approach is to provide an array of ECN values. But how big would
this be?  And how would it be packed?  

Or one could return a monotonicly increasing count of ECN failures. But
what is a failure, as there are several kinds.  Some errors should be
handled by the kernel (Routers that don't support ECN, etc.). Others
should be of interest to the application (there is congestion in the
return path).


One could also provide a error percentage, but how would this be calculated?


Anyone have any ideas or resources I could check?