Dense Wavelength Division Multiplexing Cable (DWDM). A technology used to increase the bandwidth of fibre optic cable by transmitting multiple "channels" over the same cable. In DWDM, 8 or 16 frequencies ("colors" if you prefer) are sent over the same cables simultaneously. The number of channels available is constrained by the need to use frequencies that can be amplified with Erbium Doped Fibre Amplifiers.

DWDM is currently used primarily with long haul networks. It allows the bandwidth of an existing cable to be increased without requiring the stringing of additional cables. As of 1999, off the shelf equipment will support 40G/Bit per second bidirectional communications for distances of several hundred km using 16 channels. Amplifiers are required every 80 or 120 km.

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