Star Wars Shielding

[Sea Skimmer]

They invariably are going to require use of some sort of hyperwave network if not the holonet itself to transmit signals (I doubt one could easily achieve LOS for any sort of transmission across hundreds or thousands of light years, particularily from the Deep Core.) Either they can use such nodes to order shields lowered for such communications (at least some sortts of standard comm signals apparently can pass through shields still) and then transmit the MCS signal, or (more likely) the World Devastators are programmed to communicate with Byss at preprogrammed intervals (or, quite possibly, are programmed to check the nodes for such signals at regular intervals.)

Or they have a ship in orbit that has its shields down to recieve signals and retransmits them in a radio frequency (the fact that there were communications ships in orbit supports that)

They could just be raising a communications mast through there own shields, retracting it as needed to avoid enemy attacks destroying the thing. Something similar has been done more then once with hardened radar antennas. But really, we could come up with solutions all day long for this.