The Ethernet layer 1 frame contains information that coordinates data transmission over the physical medium. This medium may be a copper cable, for example, a Cat5/Cat5e/Cat6 twisted pair or coaxial, fiber optic, or wireless. The physical layer is where data is most susceptible to faults and problems. Signals are exposed to electromagnetic interference, physical damage/degradation (for example, signal strength loss or cable breaks), and network device errors.