Aiphone IS-RS Audio Substation Aiphone IS-RS Audio Substation keeps you connected at all times. This device connects to IS-CCU, IS-SCU, or IS-RCU units, using the CAT-5e/6 cable and is a handset style, and an audio only sub-station. It can be wall mounted for easy access. Equipped with options, it can be used hands free with the internal speaker or can be tied to an external 8-ohm speaker. The external speaker is designed to page announcements too.