Apparatus and method for a non-symmetrical half-duplex DSL modem

1. A method for communicating data from a data terminal unit (DTU), the method comprising:

receiving a poll from a central office DTU, the poll comprising at least an address header;

determining if the address header identifies the DTU;

determining if a variable length frame communicated from a digital type device resides in a buffer when the address header identifies the DTU;

encapsulating the variable length frame between a second address header and a frame check sequence when the variable length frame resides in the buffer, wherein the second address header identifies at least a destination device; and

communicating the encapsulated variable length frame onto a digital subscriber line, wherein length of the encapsulated variable length frame is determined by length of the variable length frame received from the digital type device.

2. The method of claim 1 , wherein the communicating further comprises communicating the encapsulated variable length frame to the central office DTU.

3. The method of claim 1 , wherein the communicating further comprises communicating the encapsulated variable length frame to a second DTU, the second DTU residing on the subscriber line and identified by the second address header.

4. The method of claim 1 , further comprising communicating a response when the address header identifies the DTU, the response comprising at least the encapsulated variable length frame.

5. The method of claim 1 , further comprising communicating a response when the address header identifies the DTU and when no variable length frame resides in the buffer, the response comprising a third address header and the frame check sequence.

6. The method of claim 1 , further comprising communicating a response when the address header identifies the DTU and when no variable length frame resides in the buffer, wherein the response is silence from the DTU.

7. The method of claim 1 , further comprising:

starting a response when the address header identifies the DTU, a response start indicated by turning on a carrier; and

ending the response, a response end indicated by turning off the carrier.

8. The method of claim 1 , further comprising;

converting serial data streams received from the DTU into parallel data; and

storing the parallel data in a buffer, the parallel data corresponding to the variable length frame.

9. The method of claim 8 , wherein encapsulating further comprises encapsulating the parallel data between the second address header and the frame check sequence.

10. The method of claim 1 , further comprising:

communicating a telephone signal over a first frequency range; and

communicating the encapsulated variable length frame over a second frequency range, the second frequency range different from the first frequency range.

11. The method of claim 10 , further comprising communicating another signal over a third frequency range, the third frequency range different from the first frequency range and the second frequency range.

12. A central office data terminal unit (DTU) comprising:

an interface coupled to a communication system;

at least one buffer coupled to the interface and configured to receive a variable length frame from a remote digital type device, the variable length frame having an amount of data to be communicated to a remote DTU residing on a subscriber loop coupled to the central office DTU; and

a modulator/demodulator coupled to the subscriber line and the buffer, and configured to communicate a poll to the remote DTU, wherein length of the poll is determined by the amount of the data residing in the variable length frame, and wherein the modulator/demodulator is further configured to receive a response from the remote DTU, the response comprising at least a second variable length frame generated by a digital type device coupled to the remote DTU, and wherein length of the response is determined by a second amount of data residing in the second variable length frame.

13. The central office DTU of claim 12 , further comprising:

a plurality of interfaces coupled to the communication system; and

a plurality of buffers, each of the plurality of buffers uniquely coupled to one of the plurality of interfaces and configured to receive a third variable length frame from one of a plurality of remote digital type devices, the third variable length frame having data to be communicated to the remote DTU, and wherein length of the third variable length frame is determined by a third amount of data residing in the third variable length frame.

14. The central office DTU of claim 12 , wherein the modulator/demodulator is configured to encapsulate the variable length frame between an address header and a frame check sequence when the variable length frame resides in the buffer, wherein the address header identifies the remote DTU.

15. The central office DTU of claim 14 , wherein the address header uniquely identifies the remote DTU from a plurality of DTUs coupled to the subscriber line.

16. A system for communicating data from a data terminal unit (DTU), comprising:

means for receiving a poll from a central office DTU, the poll comprising at least an address header;

means for determining if the address header identifies the DTU;

means for determining if a variable length frame communicated from a digital type device resides in a buffer when the address header identifies the DTU;

means for encapsulating the variable length frame between a second address header and a frame check sequence when the variable length frame resides in the buffer, wherein the second address header identifies at least a destination device; and

means for communicating the encapsulated variable length frame onto a digital subscriber line, wherein length of the encapsulated variable length frame is determined by length of the variable length frame received from the digital type device.

17. The system of claim 16 , wherein the means for communicating further comprises means for communicating the encapsulated variable length frame to the central office DTU.

18. The system of claim 16 , wherein the means for communicating further comprises means for communicating the encapsulated variable length frame to a second DTU, the second DTU residing on the subscriber line and identified by the second address header.

19. The system of claim 16 , further comprising means for communicating a response when the address header identifies the DTU, the response comprising at least the encapsulated variable length frame.

20. The system of claim 16 , further comprising means for communicating a response when the address header identifies the DTU and when no variable length frame resides in the buffer, the response comprising only a third address header and the frame check sequence.

21. The system of claim 16 , further comprising means for communicating a response when the address header identifies the DTU and when no variable length frame resides in the buffer, wherein the response is silence from the DTU.

22. The system of claim 16 , further comprising:

means for turning on a carrier to indicate a start of a response, wherein the response comprises the encapsulated variable length frame; and

means for turning off the carrier to indicate an end of the response.

23. The system of claim 16 , further comprising:

means for converting serial data streams received from the DTU into parallel data; and

means for storing the parallel data in a buffer, the parallel data corresponding to the variable length frame.

24. The system of claim 23 , wherein the means for encapsulating further comprises means for encapsulating the parallel data between the second address header and the frame check sequence.

25. The system of claim 16 , further comprising:

means for communicating a telephone signal over a first frequency range; and

means for communicating the encapsulated variable length frame over a second frequency range, the second frequency range different from the first frequency range.

26. A system for communicating data from a central office data terminal unit (DTU), comprising:

means for communicating a poll from the central office DTU onto a subscriber line, the poll comprising a first variable length frame having at least an address header identifying a remote DTU coupled to the subscriber line, and wherein length of the first variable length frame is determined by a first amount of data; and

means for receiving a response from the remote DTU, the response comprising a second variable length frame, the second variable length frame generated by a digital type device coupled to the remote DTU, and wherein length of the response is determined by a second amount of data residing in the second variable length frame.

27. The system of claim 26 , further comprising:

means for encapsulating the second variable length frame and a second address header identifying a destination device into a frame, the second address header specified in the received response; and

means for communicating the frame onto a communication system coupled to the central office DTU, wherein length of the frame is determined by the second amount of data residing in the second variable length frame.

28. The system of claim 26 , wherein the means for communicating further comprises means for communicating the encapsulated variable length frame from the central office DTU onto a communication system.

29. The system of claim 26 , further comprising:

means for detecting a start of the response when the remote DTU turns on a carrier; and

means for detecting an end of the response when the remote DTU turns off the carrier.

30. The system of claim 26 , further comprising:

means for communicating a telephone signal onto the subscriber line over a first frequency range; and

means for communicating the poll onto the subscriber line over a second frequency range, the second frequency range different from the first frequency range.