In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i. WDM allows communication in both the directions in the fiber cable. In WDM, the optical signals from different. Internet and Data Networks: Multiplexing is used in internet communications to transmit data from multiple users over a single network line, improving the efficiency and speed of data transfer. It is used in first generation cellular telephone. This allows multiple channels of data to be transmitted simultaneously.