A method of local contrast mapping that changes the dynamic range of an original image to more closely match the dynamic range of the medium used for the reproduction. The TDM OLT communicates with a first group of customer premises via TDM signals while the WDM OLT communicates with a second group of CPs via WDM signals. As a result, it is possible to reduce a defective rate of the non-volatile semiconductor memory device. Along the lower edge is a centrally located downwardly projecting portion flanked on each side by downwardly sloping wing portions. In optional embodiments, the user can connect to the frame by way or a collarharness. The preferred embodiment provides not only a method to check data flow to optimize the method of assigning and withdrawing wireless channels assigned to the mobile station, but also a method of assigning and withdrawing wireless channels by checking a wireless environment and a data flow at the same time using NAK frame affected by wireless environment.