Full Duplex communication is the process of transferring of voice or data signals in both directions at the same time. Full duplex operation normally assigns the transmitter and receiver to different communication channels. When using Hands Free Speakerphone, you might of experience the other party fading in and out while you talk. This is because one frequency is used to communicate in one direction and the other frequency is required to communicate in the opposite direction. This is eliminated with use of a KDb-F Card on the iDCS telephones.