CAIRN is an internetwork testbed network funded primarily by the Information Technology office of the Defense Advanced Research Projects Agency (DARPA), but also supported by the NASA EOSDIS Office and NSF.
Other major testbeds are intended to demonstrate new high-speed transmission technologies and to support a variety of Computer Science research. CAIRN, in contrast, is primarily intended as a testbed for advanced computer network protocols research and development. The most salient characteristic of CAIRN is: "a network we can break".
CAIRN is a follow-on testbed to the DARPA Research Testbed network or DARTNET, built in 1991 with T1 lines. CAIRN includes DARTnet plus higher speed lines, more research sites, and a more diverse research community. However, it is likely that the name "DARTnet" will linger indefinitely as a synonym for "CAIRN".