The Physical layer is responsible for the electrical, mechanical, and procedural specification for physical links between hosts on an internetwork. It sends and receives bits and communicates directly with various types of communication media. This is where the interface between the DTE, or Data Terminal Equipment, and the DCE, or Data Circuit-Terminating Equipment, is identified. The DCE is usu. located at the SP and the DTE is an attached device (usu. a router).