Working on scalability improvements to JXTA. Lately mostly working on the transports area, but moving into the Endpoint layer with gusto!
It's always a tragedy when you have to break backwards protocol compatibility, even if it fixes an otherwise unsolvable problem. None of the attempts I have ever seen at "forward-compatible", extensible protocols have ever worked that well in practice. ATA and SCSI being prime examples.
In SCSI there is the classic problem that you can't tell what the current state of fast and wide negotiation is and that when you set it, there may be no error status returned. Of course it can also get reset by a bus reset for some devices some of the time (and you never know which ones and when the reset happens).
Finding some of the wire level protocol work for JXTA to be much the same and despairing that it has the same problems as the "prior art".