DTN uses a "store and forward" technique to send info to other spacecraft or back to NASA. It can store partial bundles of data in connection points and then forward those bundles when the next node becomes available. DTN doesn't require all nodes to be online at the same time, and that can dramatically cut down the time for data to reach its recipient. NASA's animation below explains it well:

NASA has been testing DTN for years, but this its first big deployment. While the ISS isn't exactly having issues beaming data back to the agency, the technique will be especially useful in the future, when there are more probes roaming our solar system and when we're sending spacecraft to much farther locations.