Method and system for hybrid protection in optical networks

1. A method of carrying out protection of data traffic in a multi-channel multi-section ring-like optical communications network by simultaneously using Optical Multiplexed Section (OMS) protection and Optical Channel (OCH) protection, the method comprising:

providing the OMS protection for at least one section of the network by ensuring, in case of a failure in said section, switching of the data traffic from one of said configurations to another of said configurations at each of two ends of said section;

providing the OCH protection for at least one optical channel in the network, by transmitting data related to said optical channel from one of said network elements being a source point of said channel to another of said network elements being a destination point of said channel by means of two optical signals, wherein one of said optical signals is transmitted via the main configuration and another of said optical signals is transmitted via the protecting configuration;

preliminarily applying a specific additional pilot tone for transmitting data from the source point of the OCH protected channel via a specific one of said configurations,

selecting an optical signal in an OCH protected optical channel, in case of a fault in a section of said network, by relying on an indication associated with OMS switching functionality required to overcome said fault,

wherein said step of selecting being performed by rejecting the one of the two optical signals of said OCH protected channel, that has undergone the switching from one of said configurations to another of said configurations owing to the OMS protection, the rejecting being based on detecting a discrepancy, from the point of presence of said specific pilot tone, between a received and an expected optical signal from one of said configurations at the destination point of said OCH protected channel, the discrepancy serving said indication,

wherein the communication network consisting of no more than two ring-like configurations respectively formed by no more than two optical fibers connecting network elements, one of said configurations is considered a main configuration and the other is considered a protecting configuration, and

wherein said specific optical signal in said OCH protected optical channel is selected between one signal transmitted via the main configuration and another signal transmitted via the protecting configuration.

2. The method according to claim 1 , comprising:

providing the OMS protection for at least one section of the network by ensuring, in case of a failure in said section, switching of the data traffic from one of said configurations to another of said configurations at each of two ends of said section;

providing the OCH protection for at least one optical channel in the network, by transmitting data related to said optical channel from one of said network elements being a source point of said channel to another of said network elements being a destination point of said channel by means of two optical signals being said one signal and said another signal;

said step of selecting being performed by rejecting the one of the two optical signals of said OCH protected channel, that has undergone said switching from one of said configurations to another of said configurations at least once, by relying on said indication being created in the optical signal while undergoing said switching.

3. The method according to claim 2 , comprising providing switching means for the OMS protection and wherein the step of rejecting comprises detecting said indication in the optical signal having been switched by said switching means.

4. The method according to claim 3 , wherein said indication is a momentary loss created in said signal while switching it in the switching means.

5. The method according to claim 3 , wherein said indication is a signaling artifact added to the signal that has been switched in the switching means.

6. The method according to claim 5 , wherein said signaling artifact is a modulating tone applied to the signal having been switched by said switching means.

7. The method according to claim 2 , wherein the step of providing the OCH protection comprises providing an Optical Add Drop Multiplexer (OADM) at each of the source point and the destination point of the OCH protected channel, both in the main configuration and in the protecting configuration thereof.

8. The method according to claim 2 , wherein the step of providing the OCH protection comprises arrangement thereof for a bi-directional optical channel, wherein each of the source point and the destination point serves as a source/destination point.

9. The method according to claim 8 , wherein one and the same carrier wavelength is used for transmitting data along said bi-directional OCH protected optical channel.

10. A system capable of simultaneously performing Optical Multiplex Section (OMS) protection and Optical Channel (OCH) protection of optical traffic in a multi-channel multi-section optical communications ring-like network, the system being operative to select an optical signal in an OCH protected optical channel, in case of a fault in a section of said network, by relying on an indication associated with OMS switching functionality required to overcome said fault, said system comprising:

an OMS protection arrangement for at least one section of said network, including switching means at both ends of said section,

an OCH protection arrangement for at least one optical channel formed in said network between a source point and a destination point of said channel, the OCH protection arrangement including Optical Add Drop Multiplexer (OADM) in a protecting configuration at the destination point of said optical channel,

means for rejecting use of such an optical signal related to the OCH protected optical channel, that has been switched from one of said configurations to another at least once, by relaying on said indication,

wherein said means for rejecting comprise a modulator at the source point of the OCH protected optical channel for preliminarily applying a specific pilot tone to data transmitted via said channel through a specific one of said configurations, and a tone detector at the destination point of said OCH protected optical channel for detecting said indication in the form of a discrepancy, from the point of presence of said specific pilot tone, between a received optical signal and an expected optical signal from one of said configurations at the destination point of said OCH protected optical channel, and for further rejecting the received optical signal in case the indication is detected,

wherein said network consisting of no more than two ring-like configurations respectively formed by no more than two optical fibers connecting network elements, one of said configurations is considered a main configuration and the other is considered a protecting configuration, and

wherein said specific optical signal in said OCH protected optical channel is selected between one signal transmitted via the main configuration and another signal transmitted via the protecting configuration.

11. The system according to claim 10 , wherein, said means for rejecting use, at said destination point, of such an optical signal related to the OCH protected optical channel, relies on the indication being created in said optical signal while undergoing said switching.

12. The system according to claim 11 , wherein said means for rejecting are situated at the destination point of said optical channel and comprise:

a detector of said indication associated with the switching of said optical signal in the switching means and

a selector for selecting for further use an optical signal not comprising said indication.

13. The system according to claim 12 , further comprising a generator of said indication, associated with the switching means.

14. The system according to claim 10 , wherein said OCH protected optical channel is bi-directional.

15. The system according to claim 14 , wherein one and the same carrier wavelength is used for transmitting data in said OCH protected optical channel in both said directions.