Abstract: A method and apparatus for identifying at least one characteristic of at least one optical link of an optical network. The method comprises modulating a predetermined optical channel with a predetermined frequency component, and transmitting the modulated predetermined optical channel onto an optical waveguide at a predetermined power such that at least one optical data channel co-propagating along the optical waveguide with the modulated predetermined optical channel is modulated with the predetermined frequency component.

Abstract: A method of reducing Raman tilt in a transmission apparatus capable of transmitting a plurality of signals, occupying contiguous channels in a transmission band, through a length of optical transmission cable which exhibits the Raman effect of transferring energy from the shorter wavelength signals at one end of the transmission band towards the longer wavelength signals at the other end of the transmission band, including the transmission of half the maximum number of signals at twice the normal channel frequency spacing at a higher-than-normal level and the transmission signals in selected ones, fewer than all, of the available channels at the normal channel spacing at a normal power level. As new channels are added at the lower frequency channel spacing, the powers of both neighboring channels are reduced to the normal power level.