Network system, management device, and network design method

1. A network system comprising:

a first device configured to:

determine a modulation scheme based on a degree of multilevel and a variable baud rate, and

transmit an optical signal; and

a second device coupled to the first device, and configured to:

calculate a bandwidth of the optical signal narrowed by a wavelength filter from the number of wavelength filters on a transmission route of the optical signal,

select, based on a plurality of combinations of the degree of multilevel and the baud rate according to a transmission rate of the optical signal, and a correspondence between a lower limit value of a bandwidth of the optical signal and a lower limit value of an optical signal to noise ratio (OSNR) for maintaining predetermined quality of the optical signal when the degree of multilevel and the baud rate are set in the first device, one or more first combinations in each of which the lower limit value of the bandwidth is equal to or less than the bandwidth of the narrowed optical signal from the plurality of combinations,

select a second combination from the one or more first combinations based on the lower limit value of the OSNR or the baud rate, and

set the degree of multilevel and the baud rate of the second combination in the first device.

2. The network system according to claim 1 , wherein

the degree of multilevel has digits after a decimal point, and

a multilevel modulation scheme with the degree of multilevel is a multilevel modulation scheme using probabilistic shaping.

3. The network system according to claim 2 , wherein

each of the plurality of combinations includes a basic modulation scheme, the degree of multilevel, and the baud rate, each of which is a basis for a probabilistic shaping process, and

the second device sets the basic modulation scheme, the degree of multilevel, and the baud rate of the second combination in the first device, and

the first device determines a modulation scheme based on the basic modulation scheme, the degree of multilevel, and the baud rate to transmit the optical signal.

4. The network system according to claim 1 , wherein

the second device selects the first combination in which the transmission rate is equal to or more than a predetermined value from the plurality of combinations.

5. The network system according to claim 4 , wherein

the second device selects the second combination that has a highest transmission rate from the one or more first combinations.

6. The network system according to claim 5 , wherein

the second device selects the second combination in which the lower limit value of the OSNR is smallest from the one or more first combinations.

7. The network system according to claim 1 , wherein the second device calculates a plurality of transmission routes through each of which the optical signal is transmitted, and

the second device is further configured to:

calculate a bandwidth of the optical signal after being narrowed by the wavelength filter for each of the plurality of transmission routes, for each of the plurality of transmission routes,

select the one or more first combinations from the plurality of combinations,

select the second combination from the one or more first combinations based on the lower limit value of the OSNR,

acquire an index value regarding receiving side quality of the optical signal following the selected second combination, and

select one of the plurality of transmission routes based on the index value.

8. The network system according to claim 7 , wherein the second device is further configured to:

divide a transmission route in which the index value is less than a predetermined threshold among the plurality of transmission routes into a plurality of optical terminal sections in each of which the index value is equal to or more than the predetermined threshold and the optical signal is terminated, and

selects a transmission route that has the smallest number of the plurality of optical terminal sections among the plurality of transmission routes.

9. A management device coupled to transmission device, the transmission device configured to transmit an optical signal, the management device comprising:

a memory; and

a processor coupled to memory and configured to:

calculate a bandwidth of the optical signal narrowed by a wavelength filter from the number of wavelength filters on a transmission route of the optical signal,

select, based on a plurality of combinations of a degree of multilevel and a baud rate according to a transmission rate of the optical signal, and a correspondence between a lower limit value of a bandwidth of the optical signal and a lower limit value of an optical signal to noise ratio (OSNR) for maintaining predetermined quality of the optical signal when the degree of multilevel and the baud rate are set in the transmission device, one or more first combinations in each of which the lower limit value of the bandwidth is equal to or less than the bandwidth of the narrowed optical signal from the plurality of combinations,

select a second combination from the one or more first combinations based on the lower limit value of the OSNR or the baud rate, and

set the degree of multilevel and the baud rate of the second combination in the transmission device.

10. The management device according to claim 9 , wherein

the degree of multilevel has digits after a decimal point, and

a multilevel modulation scheme with the degree of multilevel is a multilevel modulation scheme using probabilistic shaping.

11. The management device according to claim 10 , wherein

each of the plurality of combinations includes a basic modulation scheme, the degree of multilevel, and the baud rate, each of which is a basis for a probabilistic shaping process, wherein

the processor sets the basic modulation scheme, the degree of multilevel, and the baud rate of the second combination in the transmission device.

12. The management device according to claim 9 , wherein

the processor selects the first combination in which the transmission rate is equal to or more than a predetermined value from the plurality of combinations.

13. The management device according to claim 12 , wherein

the processor selects the second combination that has a highest transmission rate from the one or more first combinations.

14. The management device according to claim 13 , wherein

the processor selects the second combination in which the lower limit value of the OSNR is smallest from the one or more first combinations.

15. The management device according to claim 9 , wherein, the processor further configured to:

calculate a plurality of transmission routes through each of which the optical signal is transmitted,

calculate a bandwidth of the optical signal after being narrowed by the wavelength filter for each of the plurality of transmission routes,

for each of the plurality of transmission routes, select the one or more first combinations from the plurality of combinations,

select the second combination from the one or more first combinations based on the lower limit value of the OSNR, and acquires an index value regarding receiving side quality of the optical signal following the selected second combination, and

select one of the plurality of transmission routes based on the index value.

16. The management device according to claim 15 , wherein the processor is further configured to:

divide a transmission route in which the index value is less than a predetermined threshold among the plurality of transmission routes into a plurality of optical terminal sections in each of which the index value is equal to or more than the predetermined threshold and the optical signal is terminated, and

select a transmission route that has the smallest number of the plurality of optical terminal sections among the plurality of transmission routes.

17. A network design method, comprising:

calculating a bandwidth of an optical signal narrowed by a wavelength filter from the number of wavelength filters on a transmission route of the optical signal transmitted by a transmission device based on a degree of multilevel that has digits after a decimal point and a variable baud rate;

selecting, based on a plurality of combinations of the degree of multilevel and the baud rate according to a transmission rate of the optical signal, and a correspondence between a lower limit value of a bandwidth of the optical signal and a lower limit value of an optical signal to noise ratio (OSNR) for maintaining predetermined quality of the optical signal when the degree of multilevel and the baud rate are set in the transmission device, one or more first combinations in each of which the lower limit value of the bandwidth is equal to or less than a bandwidth of the narrowed optical signal from the plurality of combinations,

selecting a second combination from the one or more first combinations based on the lower limit value of the OSNR or the baud rate; and

setting the degree of multilevel and the baud rate of the second combination in the transmission device.