This is a pretty awesome looking protocol-- sort of like a TCP/UDP frankenstein with what they call "mult-homing" and "multi-streaming" and a couple of other goodies.
Mult-homing is the ability to split SCTP connections across networks, so like you could aggregate a bunch of networks together even if they had different IPs.
Multi-streaming is multiple streams within an association, or connection.
There are places where overhead is much higher than TCP, but also places where it's much lower. It's also included in Linux 2.6. Check out the article here: http://www.ibm.com/developerworks/linux/library/l-sctp/