Systems and methods are described for supporting synchronization status messages (SSM) on building integrated timing system synchronization supply unit (BITS-SSU) remote shelves. A method includes providing a composite clock reference to a remote synchronization supply unit from a master synchronization supply unit; providing a synchronization status message to the remote synchronization supply unit; relaying the composite clock reference from the remote synchronization supply unit; and relaying the synchronization status message from the remote synchronization supply unit. An apparatus includes: a master synchronization supply unit; and a remote synchronization supply unit coupled to the master synchronization supply unit, the remote synchronization supply unit including a composite clock reference input to receive a composite clock reference from the master synchronization supply unit, a composite clock output to relay the composite clock reference, a synchronization status message input to receive a synchronization status message, and a synchronization status message output to relay the synchronization status message.