Method and apparatus for reducing false hook detection

1. A method to reduce false switch hook detection in a line card coupled to a subscriber loop via a ring and tip terminal, comprising:

operating in a first state of the line card;

receiving a control signal;

disabling switch hook detection in the line card;

storing a value representative of a voltage level between the ring and tip terminal in response to receiving the control signal;

determining an initial condition of a second state of the line card; and

operating in the second state of the line card in response to receiving the control signal, wherein the second state begins to operate from the determined initial condition; and

providing a ringing signal to the subscriber loop, wherein the ringing signal is provided in response to the ringing signal crossing the stored voltage value.

2. The method of claim 1 , wherein receiving the control signal comprises receiving a ringing control signal.

3. The method of claim 2 , wherein operating in the first state comprises operating in at least one of a standby state and an active state of the line card.

4. The method of claim 3 , wherein determining the initial condition of the second state includes determining the initial condition of the ringing state of the line card.

5. The method of claim 4 , wherein determining the initial condition of the second state comprises determining the initial condition based on a ratio of a full scale current value in the first state and a full scale current value in the second state.

6. The method of claim 1 , further activating the switch hook detection in the line card in response to providing the ringing signal.

7. The method of claim 1 , wherein receiving the control signal comprises receiving a control signal to stop ringing providing that ring trip has not occurred.

8. The method of claim 7 , wherein operating in the first state comprises operating in a ringing state of the line card.

9. The method of claim 8 , wherein operating in the second state comprises operating in at least one of a standby state and an active state of the line card.

10. The method of claim 9 , wherein determining an initial condition of the second state of the line card comprises setting the initial condition to a value less than a switch hook threshold.

11. The method of claim 10 , wherein the second state begins to operate from the determined initial condition includes adjusting a current to the subscriber loop.

12. A method to reduce false switch hook detection in a line card coupled to a subscriber loop via a ring and tip terminal, comprising:

operating in a first state of the line card;

receiving a control signal, wherein receiving the control signal comprises receiving a ring trip detection signal to stop ringing;

disabling switch hook detection in the line card;

storing a value representative of a voltage level between the ring and tip terminal in response to receiving the control signal;

determining an initial condition of a second state of the line card;

operating in the second state of the line card in response to receiving the control signal, wherein the second state begins to operate from the determined initial condition;

providing a ringing signal to the subscriber loop; and

stopping the ringing signal in response to the ringing signal crossing the stored voltage value.

13. The method of claim 12 , wherein operating in the first state of the line card further comprises operating in a ringing state of the line card and wherein operating in the second state of the line card further comprises operating in an active state of the line card.

14. The method of claim 12 , wherein determining an initial condition of the second state of the line card further comprises setting the initial condition to a value larger than a switch hook threshold and wherein the second state begins to operate from the determined initial condition includes adjusting a current to the subscriber loop.

15. The method of claim 12 , wherein the value is retrievably stored, and further storing at least one of adaptive echo parameter, cancellation parameter, and filter coefficient.

16. An apparatus to reduce false switch hook detection, the apparatus capable of operating in at least a first and a second state, comprising:

switch hook detector; and

a processor adapted to:

receive a control signal;

store a value representative of a voltage level between a ring and tip terminal in response to receiving the control signal;

interrupt switch hook detection;

determine an initial condition of the second state;

operate in the second state in response to receiving the control signal, wherein the second state begins to operate from the determined initial condition; and

provide a ringing signal to a subscriber loop in response to the ringing signal crossing the stored voltage value.

17. The apparatus of claim 16 , wherein the processor adapted to receive a control signal comprises the processor adapted to receive a ringing control signal.

18. The apparatus of claim 17 , wherein the processor adapted to operate in the first state comprises operating in at least one of a standby state and an active state.

19. The apparatus of claim 18 , wherein the processor adapted to determine the initial condition of the second state includes the processor adapted to determine the initial condition of the ringing state.

20. The apparatus of claim 19 , wherein the processor adapted to determine the initial condition of the second state comprises the processor adapted to determine the initial condition based on a ratio of a full scale current value in the first state and a full scale current value in the second state.

21. The apparatus of claim 16 , wherein the processor is further adapted to activate the switch hook detection in the line card in response to providing the ringing signal.

22. The apparatus of claim 16 , wherein the processor adapted to receive the control signal comprises the processor adapted to receive a control signal to stop ringing.

23. The apparatus of claim 16 , wherein the processor is adapted to stop the ringing signal in response to the ringing signal crossing the stored voltage value.

24. The apparatus of claim 23 , wherein the processor adapted to operate in the first state comprises the processor adapted to operate in a ringing state and wherein the processor adapted to operate in the second state comprises the processor adapted to operate in at least one of a standby state and an active state.

25. The apparatus of claim 24 , wherein the processor adapted to determine the initial condition of the second state comprises setting the initial condition to a value less than a switch hook threshold.

26. The apparatus of claim 25 , wherein the second state begins to operate from the determined initial condition includes adjusting a current to the subscriber loop.

27. A line card, comprising:

a subscriber line interface circuit coupled to a subscriber loop via a ring and trip terminal; and

a processor coupled to the subscriber line interface circuit, wherein the processor is adapted to:

operate in a first state of the line card;

receive a control signal;

store a value representative of a voltage level between the ring and tip terminal in response to receiving the control signal;

interrupt switch hook detection in the line card;

determine an initial condition of a second operating state of the line card;

operate in the second state of the line card in response to receiving the control signal, wherein the second state begins to operate from the determined initial condition; and

provide a ringing signal to the subscriber loop in response to the ringing signal crossing the stored voltage value.

28. The line card of claim 27 , wherein the subscriber line interface circuit is a voltage-feed subscriber line interface circuit.

29. The line card of claim 27 , wherein the processor adapted to receive a control signal comprises the processor adapted to receive a ringing control signal.

30. The line card of claim 29 , where the processor adapted to operate in the first state comprises operating in at least one of a standby state and an active state of the line card.

31. An apparatus to reduce false switch hook detection in a line card coupled to a subscriber loop, comprising:

means for operating in a first state of the line card;

means for receiving a control signal;

means for disabling switch hook detection in the line card;

means for storing a value representative of a voltage level between a ring and tip terminal in response to receiving the control signal;

means for determining an initial condition of a second operating state of the line card;

means for operating in the second state of the line card in response to receiving the control signal, wherein the second state begins to operate from the determined initial condition; and

means for providing a ringing signal to the subscriber loop, wherein the ringing signal is provided in response to the ringing signal crossing the stored voltage value.

32. A method to reduce false switch hook detection in a line card coupled to a subscriber loop, comprising:

operating in a first state of the line card;

determining if a ring trip occurs;

disabling switch hook detection in the line card in response to determining that the ring trip has occurred;

determining an initial condition of a second state of the line card;

operating in the second state of the line card in response to determining the ring trip, wherein the second state begins to operate from the determined initial condition; and

providing a ringing signal to the subscriber loop, wherein the ringing signal is provided in response to the ringing signal crossing a stored voltage value.