Embodiments of the claimed subject matter provide a method and apparatus for device discovery in device-to-device communication. Monitoring is conducted to detect a degradation in performance which can be used as a factor in deciding whether tube replacement is justified. A plurality of pixel electrodes are disposed in the pixel regions. A bite valve is provided at one end of the tube to be actuated by a user’s teeth. By the layout method the cost of placing equipment at available placement sites or nodes is minimized based on various constraints, e. The polishing pad is disposed at the table.