ATM protection switching method and apparatus

1. In an ATM network, in which ATM traffic is carried on a physical network adhering to a physical layer protocol, a method of switching traffic transported on a working entity of said ATM network to a protection entity on said ATM network comprising:

a) monitoring an indicator of signal degrade of said working entity provided by said physical layer protocol;

b) in response to detecting a degraded signal as a result of said monitoring, generating ATM cells indicative of said signal degrade on said ATM network.

2. The method of claim 1 , further comprising:

c) in response to said ATM cells indicative of said signal degrade, receiving said traffic on said protection entity.

3. The method of claim 2 , further comprising:

d) in response to said ATM cells indicative of said signal degrade, transmitting said traffic on said protection entity from a source network element.

4. The method of claim 1 , wherein said physical network comprises a synchronous optical network (“SONET”).

5. The method of claim 4 , wherein said monitoring comprises calculating a bit-error-rate from SONET path overhead.

6. The method of claim 5 , wherein said calculating utilizes a parity check field within said SONET path overhead to determine said bit error rate.

7. The method of claim 6 , wherein said ATM cells indicative of signal degrade are generated in response to said bit-error-rate exceeding a defined threshold.

8. The method of claim 7 , wherein said ATM cells comprise ATM alarm indication signal (“AIS”) cells.

9. The method of claim 8 , wherein said AIS cells are transmitted from a network element detecting said signal degrade to a downstream network element using an ATM signaling channel.

10. The method of claim 9 , wherein said ATM signaling channel comprises an ATM protection switching channel.

11. The method of claim 7 , wherein said ATM cells comprise an ATM protection switching coordination protocol (“CP”) cell.

12. The method of claim 11 , wherein said CP cell is transmitted within one of said working entity and said protection entity.

13. A network element for use in an ATM network, in which ATM traffic is carried on a physical network adhering to a physical layer protocol, said network element operable to cause traffic transported on a working entity of said ATM network to be transported on a protection entity on said ATM network, said network element comprising:

a detector for monitoring an indicator of signal degrade of said working entity provided by said physical layer protocol, and generating a trigger indicative of signal degrade on said working entity to cause said network element to generate ATM cells indicative of said signal degrade on said ATM network.

14. The network element of claim 13 , further comprising an ATM switch, in communication with an ATM processor, wherein said detector is in communication with said ATM processor, and wherein said ATM processor generates ATM cells indicative of signal degrade in response to said trigger.

15. The network element of claim 13 , wherein said ATM cells comprise ATM alarm indication signal (“AIS”) cells.

16. The network element of claim 13 , wherein said ATM cells comprise an ATM protection switching coordination protocol (“CP”) cell.

17. The network element of claim 15 , wherein said AIS cells are transmitted to a downstream network element using an ATM signaling channel.

18. A network element for use in an ATM network, in which ATM traffic is carried on a physical network adhering to a physical layer protocol, said network element operable to switch traffic transported on a working entity of said ATM network to a protection entity on said ATM network, said network element comprising:

means for monitoring an indicator of signal degrade at said physical layer of said working entity provided by said physical layer protocol;

means for generating ATM cells indicative of signal degrade in response to said means for monitoring signal degrade at said physical layer.

19. Computer memory storing program instructions, adapting an ATM network element on ATM network in which ATM traffic is carried on a physical network adhering to a physical layer protocol, to:

a) monitor an indicator of signal degrade of a working entity on said ATM network provided by said physical layer protocol;

b) in response to detecting a degraded signal as a result of said monitoring, generate ATM cells indicative of said signal degrade on said ATM network.

20. An ATM cell comprising an alarm indication signal (“AIS”), embodied in a carrier wave to be transported on an ATM network, said cell comprising:

a) a field identifying said cell as an ATM AIS cell;

b) a field including an indicator of signal degrade on said network.

21. In a communications network in which ATM traffic is transported on a SONET network a method of switching traffic transported on a working ATM entity to a protection ATM entity, said method comprising:

a. monitoring an indicator of signal degrade of said working entity by monitoring an indicator of signal degrade in SONET overhead on said SONET network;

b. in response to detecting a degraded signal as a result of said monitoring, generating ATM cells indicative of the signal degrade to be transported to at least one adjacent node on said network.

22. The method of claim 21 , further comprising:

c) in response to said ATM cells indicative of said signal degrade, receiving said traffic on said protection entity.

23. The method of claim 21 further comprising:

d) in response to said ATM cells indicative of said signal degrade, transmitting said traffic on said protection entity from a source network element.

24. The method of claim 21 , wherein said monitoring comprises calculating a bit-error-rate from SONET path overhead.

25. The method of claim 24 , wherein said calculating utilizes a parity check field within said SONET path overhead to determine said bit error rate.