Method for providing fault tolerance in an XDSL system

1. A method for performing a switchover in an XDSL system, the method comprising:

synchronizing a standby unit to an active unit, wherein the active unit connects with a far end unit over a transmission line, wherein the active unit includes a processor and analog circuits, wherein the standby unit includes a processor and analog circuits, and wherein synchronizing the active unit with the standby unit comprises:

synchronizing the processor in the standby unit to the processor in the active unit; and

synchronizing the analog circuits in the standby unit to the analog circuits in the active unit;

receiving a first transmission signal at the active unit from the far end unit;

providing the first transmission signal from the active unit to the standby unit; and

updating a current state of the standby unit based on the first transmission signal.

2. The method of claim 1 , further comprising:

detecting an indication within the XDSL system to switch from the active unit to the standby unit;

isolating the active unit from the transmission line; and

connecting the standby unit to the transmission line.

3. The method of claim 2 , wherein the indication is a fault.

4. The method of claim 2 , further comprising:

receiving a second transmission signal at the standby unit from the far end unit over the transmission line; and

updating the current state of the standby unit based on the second transmission signal.

5. The method of claim 1 , wherein synchronizing the standby unit with the active unit comprises:

sending state information from the active unit to the standby unit.

6. The method of claim 5 , wherein the state information includes performance monitoring information.

7. The method of claim 5 , wherein the state information includes configuration information.

8. The method of claim 1 , wherein the processor in the active unit stores state information, wherein the state information is stored in a database, and wherein synchronizing the processor in the active unit further comprises:

accessing the state information stored in the database; and

sending the state information to the standby unit.

9. The method of claim 8 , wherein the state information includes performance monitoring information for the transmission line.

10. The method of claim 8 , wherein the state information includes configuration information.

11. The method of claim 8 , wherein the state information includes a signal-to-noise ratio and an attenuation characteristic for the transmission line.

12. The method of claim 8 , wherein the state information includes a line rate for the transmission line, a transmit power, and a target margin.

13. The method of claim 1 , wherein synchronizing the processor in the standby interface with the processor in the active unit comprises:

sending a current state of the processor in the active unit to the processor in the standby interface; and

setting a current state of the processor in the standby unit to reflect a current state of the processor in the active unit.

14. The method of claim 1 , wherein the transmission line carries TDM signals.

15. The method of claim 1 , wherein the XDSL system is an ADSL, G.SHDSL, VDSL, SDSL, HDSL, HDSL2 or HDSL4 system.

16. A method for providing redundancy in an XDSL system, the method comprising:

receiving state information for an active unit;

setting a current state for a processor in a standby unit using the state information for the active unit;

receiving simulated transmission information from a far end unit, wherein the simulated transmission information represents data received from the far end unit at the active unit; and

updating the current state for the processor based on the simulated transmission information received from the far end unit.

17. The method of claim 16 , wherein the state information includes performance monitoring information.

18. The method of claim 16 , wherein the state information includes configuration information.

19. The method of claim 16 , wherein the XDSL system is an ADSL, G.SHDSL, VDSL, SDSL, HDSL, HDSL2 or HDSL4 system.

20. A method for synchronizing a standby unit in an XDSL system, the method comprising:

obtaining a first data signal transmitted to an active unit over a first transmission line;

estimating a signal spectrum for the first data signal as received at the active unit;

creating a second data signal, wherein the second data signal represents the signal spectrum of the first data signal as received at the active unit; and

transmitting the second data signal to the standby unit over a second transmission line.

21. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim 20 .

22. The method of claim 20 , wherein the first and second transmission lines carry TDM signals.

23. The method of claim 20 , wherein the XDSL system is an ADSL, G.SHDSL, VDSL, SDSL, HDSL, HDSL2 or HDSL4 system.

24. A method for switching between line circuits in a TDM system, wherein the TDM system includes a plurality of line circuits in an active unit, wherein each of the plurality of line circuits connects to a different far end unit, wherein the TDM system further includes a plurality of line circuits in a standby unit, wherein each of the plurality of circuits in the active unit corresponds to one of the plurality of circuits in the standby unit, and wherein the standby unit connects to the active unit, the method comprising:

synchronizing the plurality of line circuits in the standby unit with the plurality of line circuits in the active unit;

receiving data for at least one line circuit in the active unit from the far end unit;

updating a current state of the at least one line circuit in the active unit based on the data received from the far end unit; and

updating a current state of a corresponding line circuit in the standby unit to reflect the current state of the at least one line circuit in the active unit.

25. The method of claim 24 , wherein updating the current state of the corresponding line circuit comprises:

receiving signals over at least one connection between the active unit and the standby unit; and

updating the current state of the corresponding line circuit based on the signal received over the connection.

26. The method of claim 25 , further comprising:

receiving an indication to switch from the active unit to the standby unit;

disconnecting the active unit from the far end units; and

connecting the standby unit to the far end units.

27. The method of claim 26 , wherein the indication is a fault.

28. The method of claim 24 , wherein the plurality of line circuits in the standby unit each connect to a different standby far end unit, wherein updating the current state of the corresponding line circuit comprises:

receiving a simulated transmission signal from the standby far end unit connected to the corresponding line circuit; and

updating the current state of the corresponding line circuit based on the simulated transmission information received from the standby far end unit.

29. The method of claim 28 , further comprising:

receiving an indication to switch from the active unit to the standby unit;

disconnecting the active unit from the far end units;

disconnecting the standby unit from the standby far end units; and

connecting the standby unit to the far end units.

30. The method of claim 29 , wherein the indication is fault.

31. The method of claim 24 , wherein the TDM system is an XDSL system.