An overhead processor processes overhead bytes in a stream of Synchronous Optical Network frames in multiple levels. By this, data communication efficiency is enhanced in a communication environment for communicating a communication terminal equipment on a cable network through a radio line or another access link. To prevent confusing a left ventricle beat for a left atrium beat, some devices use cross-chamber blanking, a technique which disables sensing of atrial beats for a certain time period after sensing. The reflective layer is located on the first type semiconductor layer.