The Trill defense perimeter was a network of drones stationed in orbit of Trill. During the Dominion War, Jadzia Dax upgraded the drones used in the defense perimeter in case the Dominion should attack. In 2376, Verad Kalon was able to get information on the defense perimeter after torturing Ezri Dax and the Dax symbiont and used the drones to attack the USS Enterprise and the USS Defiant. Elias Vaughn's crew were able to find the shield frequency that the drones were using and the Defiant and the Enterprise proceeded to destroy them. (ST - Divided We Fall comic: "United We Stand")