DCCP is the Datagram Congestion Control Protocol. A very quick and easy way to think about it is as UDP with congestion control. The DCCP specification is still under development: see this page for more information. The announcement for these patches (including caveats) is here

In 2002 I worked on a research Linux Kernel implementation of DCCP. My implementation runs inside the kernel as a new transport layer on top of IP, using protocol number 33. My patches are currently against version 2.4.18 of the kernel. Whether or not they apply to other versions is anyone's guess. (Actually, I know they are pretty portable but can't say with certainty to which versions - so stick with 2.4.18 for now.)

The patch files are here, their filenames represent the date of their respective snapshots.

A production level implementation of DCCP is in "modern" 2.6 Linux kernels - these patches should only be of historical interest. They did form an inspirational basis for the code that made it way into the kernel, but not much of the implementation is left. That's ok, that is what a prototype should do.