The capacity of a network is mainly dependent on the type of signalling scheme employed on transmitting and receiving end. In the earlier days, a single wavelength light beam was used to transmit data, which limited the bandwidth to the maximum operating frequency of the transmitting and receiving end equipment. With the application of wavelength division multiplexing (WDM), the bandwidth of OTN has risen up to 100Gbit/s (OTU4 Signal), by emitting light beams of different wavelengths.