SYSTEM AND METHOD FOR SELECTING AN OPTICAL PATH IN AN OPTICAL NETWORK

1 . A method for selecting an optimal optical path through which to transmit an optical signal, the optimal optical path being one of a plurality of optical paths in a transparent optical network, each of the plurality of optical paths including a plurality of optical elements, the method comprising the steps of:

determining, for each of the plurality of optical paths, a first optical signal to noise ratio for each optical element in the respective optical path;

modeling, for each of the plurality of optical paths, nonlinear distortions caused by each optical element in the respective optical path as Gaussian noise;

determining, for each of the plurality of optical paths, a second optical signal to noise ratio associated with the modeled Gaussian noise of each optical element in the respective optical path; and

selecting the optimal optical path using the sums of the first and second optical signal to noise ratios, respectively, of the optical elements in each of the plurality of optical paths.

2 . The method of claim 1 , wherein the step of selecting the optimal optical path further comprises the steps of:

calculating, using the sums of the first and second optical signal to noise ratios, respectively, an estimate of the bit error rate of each of the plurality of optical paths; and

selecting the optical path with the lowest estimated bit error rate as the optimal optical path.

3 . The method of claim 2 , wherein the step of calculating an estimate of the bit error rate further comprises:

calculating the estimate of the bit error rate of each of the plurality of optical paths using at least one of the chromatic dispersion and the polarization mode dispersion of the respective optical path.

4 . The method of claim 1 , further comprising the steps of:

generating a quality of transmission message for each of the plurality of optical paths, each quality of transmission message comprising values for parameters associated with the first and second signal to noise ratios of the respective optical path;

propagating each quality of transmission message through the plurality of optical elements along the respective optical path;

updating each quality of transmission message to reflect the sums of the first and second signal to noise ratios, respectively, of each element through which the quality of transmission message is propagated; and

forwarding the quality of transmission message to a routing tool for use in selection of the optimal path, once the quality of transmission message has been propagated to the end of the path.

5 . The method of claim 4 , wherein the quality of transmission message is implemented using an extension of the Open Shortest Path First and/or the Resource Reservation Protocol-Traffic Engineering protocols of the Generalised Multi-Protocol Switching protocol.

6 . A computer program comprising computer program code means adapted to perform all of the steps of claim 1 when the program is run on a computer.

7 . A computer program as claimed in claim 6 embodied on a computer readable medium.

8 . A system for selecting an optimal optical path through which to transmit an optical signal, the optimal optical path being one of a plurality of optical paths in a transparent optical network, each of the plurality of optical paths including a plurality of optical elements, the system comprising:

first optical signal to noise ratio determining means arranged to determine, for each of the plurality of optical paths, a first optical signal to noise ratio for each optical element in the respective optical path;

modeling means arranged to model, for each of the plurality of optical paths, nonlinear distortions caused by each optical element in the respective optical path as Gaussian noise;

second optical signal to noise ratio determining means arranged to determine, for each of the plurality of optical paths, a second optical signal to noise ratio associated with the modeled Gaussian noise of each optical element in the respective optical path; and

selecting means arranged to select the optimal optical path using the sums of the first and second optical signal to noise ratios, respectively, of the optical elements in each of the plurality of optical paths.

9 . The system of claim 8 , wherein the selecting means further comprise:

calculating means arranged to calculate, using the sums of the first and second optical signal to noise ratios, respectively, an estimate of the bit error rate of each of the plurality of optical paths; and

selecting means arranged to select the optical path with the lowest estimated bit error rate as the optimal optical path.

10 . The system of claim 9 , wherein the calculating means further comprise:

calculating means arranged to calculate the estimate of the bit error rate of each of the plurality of optical paths using at least one of the chromatic dispersion and the polarization mode dispersion of the respective optical path.

11 . The system of claim 8 further comprising:

quality of transmission generating means arranged to generate a quality of transmission message for each of the plurality of optical paths, each quality of transmission message comprising values for parameters associated with the first and second signal to noise ratios of the respective optical path;

propagating means arranged to propagate each quality of transmission message through the plurality of optical elements along the respective optical path;

updating means arranged to update each quality of transmission message to reflect the sums of the first and second signal to noise ratios, respectively, of each element through which the quality of transmission message is propagated; and

forwarding means arranged to forward the quality of transmission message to a routing tool for use in selection of the optimal path, once the quality of transmission message has been propagated to the end of the path.

12 . The system of claim 11 , wherein the quality of transmission message is implemented using an extension of the Open Shortest Path First and/or the Resource Reservation Protocol-Traffic Engineering protocols of the Generalised Multi-Protocol Switching protocol.