Board Thread:Episode Discussion/@comment-410526-20151226171120/@comment-4010415-20151227011640

Well, Ozpin did say that Kingdoms were originally only able to have radio frequencies communicate within the Kingdom itself but not the outside world, until the CCTs were built.

He also said that, the farther you get from a Kingdom, the weaker and more unreliable the signal gets, so they had to build smaller transmit towers outside the Kingdoms. However, those towers tend to get destroyed by Grimm.

So, basically, the deal with the CCTs is that they use each other in order for the signal to actually manage to reach every Kingdom. If one falls, the others don't have that bridge needed to reach other Kingdoms.