Controlling stations' access to a communications medium
View Patent ↗Managing access to a time-slotted communications medium by masking interrogatory codes that are contained in signals demarcating time slots of the medium and comparing the masked interrogatory codes against masked response codes. Access to the medium is dependent on the outcome of these comparisons.
1. A method of operating a station to selectively access a communications medium that is divided into time slots by demarcation signals transmitted from a controller at regular intervals, the method comprising:
receiving a demarcation signal that demarcates a respective one of the time slots and that contains one or more interrogatory codes and a control mask;
masking each of the one or more interrogatory codes from the received demarcation signal with the control mask to produce, for each interrogatory code, a respective masked interrogatory code;
masking a response code stored in the station with the control mask to produce a masked response code;
barring an attempt to access the communications medium in the respective time slot demarcated by the received demarcation signal if none of the one or more masked interrogatory codes matches the masked response code;
joining a network maintained by the controller; and
receiving, from the controller, a control signal containing a new response code.
2. The method of claim 1 , further comprising:
creating the response code by hashing a medium access control (MAC) address of the station.
3. The method of claim 1 , wherein the response code is a random number.
4. The method of claim 1 , wherein the control signal further includes a new control mask.
5. The method of claim 4 , wherein the control mask and the new control mask are binary words of equal length containing bits in either a one state or a zero state, the method further comprising:
selecting the one of the control mask and the new control mask that contains the most bits in the zero state for masking the one or more interrogatory codes and the response code.
6. The method of claim 1 , wherein the control mask, the response code, and the one or more interrogatory codes are binary words.
7. The method of claim 1 , further comprising:
deriving a modified control mask from the control mask.
8. The method of claim 7 , wherein the control mask is a binary word containing bits in either a one state or a zero state, wherein deriving the modified control mask comprises changing one or more bits in the binary word from the zero state to the one state.
9. A station for accessing a communications medium that is divided into time slots by demarcation signals transmitted from a controller at regular intervals, the station comprising:
a receiver configured to receive, from the controller, a demarcation signal that demarcates a respective one of the time slots;
a memory storing a response code; and
a processor configured to:
recover one or more interrogatory codes from the demarcation signal;
recover a control mask from the demarcation signal;
mask each of the one or more interrogatory codes recovered from the received demarcation signal with the control mask to produce for, each interrogatory code, a respective masked interrogatory code;
mask the response code stored in the memory with the control mask to produce a masked response code;
bar an attempt to access the communications medium in the respective time slot demarcated by the received demarcation signal if none of the one or more masked interrogatory codes matches the masked response code; and
recover a new response code from a control signal that is received from the controller in response to the station joining a network maintained by the controller.
10. The station of claim 9 , wherein the response code is a hash of a medium access control (MAC) address of the station.
11. The station of claim 9 , wherein the response code is a random number.
12. The station of claim 9 , wherein the processor is further configured to recover a new control mask from the control signal.
13. The station of claim 9 , wherein the control mask and the new control mask are binary words of equal length containing bits in either a one state or a zero state, and the processor is further configured to select the one of the control mask and the new control mask that contains the most bits in the zero state to mask the one or more interrogatory codes and the response code.
14. The station of claim 9 , wherein the control mask, the response code, and the one or more interrogatory codes are binary words.
15. The station of claim 9 , wherein the processor is further configured to derive a modified control mask from the control mask contained in the demarcation signal that corresponds to the particular time slot, the modified control mask to mask the one or more interrogatory codes and the response code.
16. The station of claim 15 , wherein the control mask is a binary word containing bits in either a one state or a zero state, and the processor is configured to derive the modified control mask by changing one or more bits in the binary word from the zero state to the one state.
17. The station of claim 15 , wherein the modified control mask is derived in response to a collision on the communications medium.
18. The method of claim 7 , wherein the modified control mask is derived in response to a collision on the communications medium.
19. A station configured to access a communications medium that is divided into time slots by demarcation signals transmitted from a controller at regular intervals, the station comprising:
means for receiving a demarcation signal that demarcates a respective one of the time slots and that contains one or more interrogatory codes and a control mask;
means for masking each of the one or more interrogatory codes from the received demarcation signal with the control mask to produce, for each interrogatory code, a respective masked interrogatory code;
means for masking a response code stored in the station with the control mask to produce a masked response code;
means for barring an attempt to access the communications medium in the respective time slot demarcated by the received demarcation signal if none of the one or more masked interrogatory codes matches the masked response code;
means for joining a network maintained by the controller; and
means for receiving, from the controller, a control signal containing a new response code.
20. The station of claim 19 , further comprising:
means for creating the response code by hashing a medium access control (MAC) address of the station.
21. The station of claim 19 , wherein the response code is a random number.
22. The station of claim 19 , wherein the control signal further includes a new control mask.
23. The station of claim 22 , wherein the control mask and the new control mask are binary words of equal length containing bits in either a one state or a zero state, the station further comprising:
means for selecting the one of the control mask and the new control mask that contains the most bits in the zero state for masking the one or more interrogatory codes and the response code.
24. The station of claim 19 , wherein the control mask, the response code, and the one or more interrogatory codes are binary words.
25. The station of claim 19 , further comprising: means for deriving a modified control mask from the control mask.
26. The station of claim 25 , wherein the control mask is a binary word containing bits in either a one state or a zero state, wherein deriving the modified control mask comprises changing one or more bits in the binary word from the zero state to the one state.
27. The station of claim 25 , wherein the modified control mask is derived in response to a collision on the communications medium.