Method and system for detecting false packets in wireless communications systems

• US 7,385,929 B1
• Filed: 09/25/2001
• Issued: 06/10/2008
• Est. Priority Date: 09/25/2001
• Status: Active Grant

• Current Assignee: The Connectivity Patent Trust
• Original Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Inventors: McFarland, William J., Thomson, John S.
• Primary Examiner(s): Pham; Chi
• Assistant Examiner(s): HOM, SHICK C
• Application Number:
  US09/963,217
• Time in Patent Office: 2,450 Days
• Field of Search: 370/241, 370/242, 370/243, 370/244, 370/245, 370/246, 370/252, 370/241.1, 714/45, 714/703, 714/738, 714/799, 714/800, 714/811, 714/818, 714/819
• US Class Current: 370/243
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0063 Single parity check
• CPC Class Codes: H04L 1/242 by comparing a transmitted test signal with a locally generated replica

Abstract

Specific bits of an incoming transmission are compared against a predetermined bit pattern. If the selected bits do not match the predetermined bit pattern, then the incoming transmission is rejected as a false packet. The predetermined bit pattern can include legal values for predetermined bits in a plurality of fields. Notably, these legal values are set by a networking standard. A parity check may check may be performed in addition to checking for predetermined bits in other fields. A user interface can be used to determine the predetermined bit pattern.

Claims

1. A method for detecting a false packet, the method comprising:

receiving a transmission;

accessing bit information regarding a plurality of fields of a valid packet, wherein each field includes at least one predetermined bit, and wherein the bit information includes legal values for the predetermined bits as set by a networking standard, wherein the predetermined bits include at least one of a rate bit, a length bit, a reserved bit, and a service bit;

identifying bits of the transmission;

comparing identified bits of the transmission to the legal values for the predetermined bits; and

rejecting the identified bits as a false packet if a comparison of the identified bits and the legal values do not match.

2. The method according to claim 1, wherein said step of comparing does not include parity bit calculations.

3. The method according to claim 1, wherein said step of rejecting comprises resetting a receiver device that receives the transmissions.

4. The method according to claim 1, wherein said step of rejecting comprises the steps of,

clearing a line busy signal used by at least one of a receiver and a transmitter.

5. The method according to claim 1, wherein said legal values comprise at least one of specific bit values and ranges of bit values.

6. The method according to claim 1, wherein said step of rejecting comprises rejecting other bits associated with the identified bits as the false packet.

7. The method according to claim 1, wherein the legal values corresponding to length bits specify a range of values.

8. The method according to claim 1, wherein the predetermined bits include a parity bit.

9. The method according to claim 1, wherein the identified bits comprise any bits that have at least one of a fixed value and a range of values.

10. The method according to claim 9, wherein said fixed value and range of values are not determined via a parity calculation.

11. The method according to claim 1, further comprising the step of setting at least one legal value based on a user input.

12. The method according to claim 1, further comprising the step of programming the legal values.

13. The method according to claim 1, further comprising the step of writing the legal values to a register for use by said comparing step.

14. The method according to claim 13, wherein said step of writing comprises running a program configured to write said register.

15. The method according to claim 14, wherein said program is a software program configured to determine the legal values and write them to the register.

16. The method according to claim 14, wherein said program is a firmware based program configured to read the legal values and write them to the register.

17. The method according to claim 14, wherein said program is a programmable logic device configured to determine the legal values and write them to the register.

18. The method according to claim 14, wherein said program is controlling software that implements said method.

19. The method according to claim 14, wherein said program is device software.

20. The method according to claim 1, further comprising the step of calculating at least a portion of the legal values.

21. The method according to claim 1, wherein said transmission is an OFDM transmission.

22. The method according to claim 1, wherein said transmission is a wireless transmission.

23. The method according to claim 1, wherein said transmission is an 802.11a transmission.

24. The method according to claim 1, wherein said legal values match selected bits from an 802.11a packet.

25. The method according to claim 1, wherein said legal values are determined prior to receipt of the transmission.

26. The method according to claim 1, wherein said transmission is a wireless transmission and said legal values match selected bits from a packet protocol.

27. The method according to claim 1, further comprising the step of choosing the legal values.

28. The method according to claim 27, wherein the legal values include bit patterns chosen based on previously received packets.

29. The method according to claim 1, further comprising:

testing values used in a field of received packets to determine a range of legal values being transmitted in the tested field; and

adding the tested field to the plurality of fields and adding the range of legal values to the bit information.

30. The method according to claim 29, wherein said step of testing includes the step of checking to determine if received packets are valid, and, disregarding invalid packets.

31. The method according to claim 29, wherein said step of testing comprises testing values of fields within packets of the transmission to determine if they are being used.

32. The method according to claim 30, wherein said step of checking comprises performing an FCS test on the received packets.

33. The method according to claim 29, wherein the tested field is a service field.

34. The method according to claim 29, wherein the tested field includes at least one of rate bits, length bits, reserved bits, and service bits.

35. The method according to claim 29, wherein the received packets are 802.11a packets.

79. The method according to claim 1, further comprising a step of choosing fields of a packet that comprise the identified bits.

80. The method according to claim 79, wherein the step of choosing fields comprises choosing fields based on previously received packets.

36. A device for detecting a false packet, the device comprising:

a receiver configured to receive incoming transmissions;

a bit recognition device configured to recognize selected bits from an incoming transmission;

storage for bit information regarding a plurality of fields of a valid packet, wherein each field includes at least one predetermined bit, and wherein the bit information includes legal values for the predetermined bits as set by a networking standard, said predetermined bits comprising at least one of a data rate bit, a length bit, and another predetermined bit, and said storage comprising a register configured to store the legal values;

a comparator configured to compare the selected bits to the legal values, said comparator comprising a logic device configured to compare the legal values against at least one of the selected bits; and

a rejection device configured to reject the incoming transmission if the selected bits do not match the legal values.

37. The device according to claim 36, wherein the incoming transmission comprises a packet.

38. The device according to claim 36, wherein said bit recognition device comprises a state machine configured to identify bits from the incoming transmission.

39. The device according to claim 36, wherein the rejection device comprises a Medium Access Control device.

40. The device according to claim 36, further comprising:

a packet reject line coupled between said comparator and said rejection device,

wherein;

said comparator is further configured to assert the packet reject line if the selected bits do not match the legal values; and

said rejection device is further configured to reject the incoming transmission if the packet reject line is asserted.

41. The device according to claim 40, further comprising a state machine coupled to the incoming transmission and the packet reject line and configured to produce at least a part of a timing of a channel busy signal based on the packet reject line.

42. The device according to claim 40, further comprising:

a transmitter coupled to the channel busy signal;

wherein said transmitter is configured to allow transmissions based on the channel busy signal.

43. The device according to claim 40, wherein:

said receiver is coupled to the packet reject line; and

said receiver is further configured to reset based on assertion of the packet reject line.

44. The device according to claim 36, further comprising a channel busy line and a state machine configured to assert the channel busy signal when the receiver receives a transmission and clear the channel busy line when an incoming transmission is rejected.

45. The device according to claim 36, further comprising:

memory elements configured to store the selected bits,

wherein said comparator is coupled to said register and the memory elements.

46. The device according to claim 45, wherein said comparator is coupled to each memory element and each register location in the register.

47. The device according to claim 36, wherein the selected bits have set values or a range of values that correspond to the legal values.

48. The device according to claim 36, wherein said bit recognition device is configured to recognize at least one of data rate bits, reserved bits, length bits, and service field bits in a packet of the incoming transmission.

49. The device according to claim 36, further comprising:

a demodulator configured to demodulate received transmissions; and

a packet reject line coupled between said comparator and said demodulator,

wherein said comparator is further configured to assert the packet reject line if the selected bits do not match the legal values, and

wherein said demodulator is further configured to reset if the packet reject line is asserted.

50. The device according to claim 36,

wherein the comparator comprises comparison logic coupled to said register.

51. The device according to claim 50, further comprising:

an input device configured to write the legal values in said register.

52. The device according to claim 51, wherein said input device includes software that queries a user for the legal values to be used.

53. The device according to claim 51, wherein said input device includes software that reads the legal values.

54. The device according to claim 36, wherein said incoming transmissions are wireless.

55. The device according to claim 36, wherein said incoming transmissions are OFDM transmissions.

56. The device according to claim 36, wherein said incoming transmissions are wireless communications conforming to a LAN protocol.

57. The device according to claim 36, wherein said incoming transmissions are 802.11a transmissions.

58. The device according to claim 36, wherein said incoming transmissions are 802.11-like transmissions.

59. The device according to claim 36, wherein said incoming transmissions are wire line transmissions.

60. The device according to claim 36, wherein the storage includes a table of the legal values for at least part of the selected bits.

61. A computer readable media having instructions stored thereon that, when loaded into a computer, cause the computer to perform steps comprising:

accessing bit information regarding a plurality of fields of a valid packet, wherein each field includes at least one predetermined bit, and wherein the bit information includes legal values for the predetermined bits as set by a networking standard, wherein said predetermined bits include at least one of a rate bit, a length bit, a reserved bit, and a service bit; and

loading the legal values into a register,

wherein said register is coupled to a packet screening device that validates incoming packets by comparing the incoming packets to the legal values.

62. The computer readable media according to claim 61, wherein said legal values are not determined via parity calculations.

63. The computer readable media according to claim 61, wherein said legal values comprise ranges of valid bit values.

64. The computer readable media according to claim 61, wherein said predetermined bits include a parity bit.

65. The computer readable media according to claim 61, wherein said legal values comprise any value of a standard of a protocol of the incoming packets, a standard of a device transmitting, receiving or storing the incoming packets, and a standard of any implementation of a device transmitting, receiving, or storing the incoming packets.

66. The computer readable media according to claim 61, wherein said register comprises a software register configured to maintain specific bit values and ranges of bit values.

67. A device, comprising:

means for receiving a transmission;

means for accessing bit information regarding a plurality of fields of a valid packet, wherein each field includes at least one predetermined bit, and wherein the bit information includes legal values for the predetermined bits as set by a networking standard, wherein the predetermined bits include at least one of a length bit, a rate bit, a reserved bit, and a service bit;

means for comparing identified bits of the transmission to the legal values to determine if the identified bits are part of a valid packet; and

means for rejecting the identified bits as a false packet if a comparison of the identified bits and the legal values do not match.

68. The device according to claim 67, wherein said legal values include a parity based pattern.

69. The device according to claim 67, wherein the identified bits include at least one of a length bit, a rate bit, and other reserved fixed value bits.

70. The device according to claim 67, wherein said legal values comprise at least one of a set value and a range of values.

71. The device according to claim 67, wherein said transmission is a packet.

72. The device according to claim 67, wherein said transmission is an OFDM transmission.

73. The device according to claim 67, wherein said transmission is a wireless transmission.

74. The device according to claim 67, wherein said transmission is a wireless 802.11a packet transmission.

75. The device according to claim 67, further comprising:

means for testing values used in the plurality of fields of received packets to determine a range of the legal values being transmitted in the tested fields; and

means for adding the tested fields and adding corresponding comparison data to the bit information.

76. The device according to claim 67, further comprising means for choosing a legal value.

81. The device according to claim 67, further comprising means for choosing fields of a packet that comprise the identified bits.

82. The device according to claim 81, wherein said means for choosing fields comprises means for choosing fields based on previously received packets.

77. A method comprising the steps of:

receiving a transmission;

identifying predetermined bits of the transmission;

comparing identified bits to legal values to determine if the identified bits are part of a valid packet; and

rejecting the identified bits as a false packet if comparison of the identified bits and the legal values do not match;

wherein;

said step of identifying comprises identifying at least one predetermined bit of the transmission that is not a parity bit;

said step of comparing does not include parity bit calculations;

said legal values include patterns determined by other than parity calculations;

said step of rejecting comprises,

rejecting an incoming packet associated with the identified bits as the false packet,

clearing a line busy signal used by one of a receiver and a transmitter; and

resetting a receiver device that receives transmissions;

said legal values comprise set bit values and ranges of bit values corresponding to the identified bits;

the identified bits comprise rate bits, length bits, reserved bits, service bits, and parity bits having set bit values and ranges of values;

said set bit values and said ranges of values are based on at least one of a packet protocol standard, a device standard, and an implementation specific standards of a communications system receiving said transmission;

said method further comprises the step of setting the legal values based on a user input, including the steps of,

displaying a user interface,

retrieving user inputs regarding the set bit values and the ranges of values of the legal values,

storing the legal values, and

running a program that performs a step of writing the legal values to a register for use by said comparing step;

said transmission is a wireless OFDM 802.11a packet transmission; and

said legal values corresponds to selected bits from an 802.11a packet.

78. A device, comprising:

a receiver configured to receive incoming transmissions;

a bit slice recognizer configured to recognize selected bits from an incoming transmission;

a comparator configured to compare the selected bits to legal values; and

a rejection device configured to reject the incoming transmission if the selected bits do not match the legal values;

wherein;

the incoming transmission comprises an OFDM encoded 802.11a wireless packet;

said bit slice recognizer comprises a state machine configured to identify the selected bits from the incoming transmission;

said rejection device comprises a Medium Access Control device;

the device further comprises a packet reject line coupled between said comparator and said rejection device;

said comparator is further configured to assert the packet reject line if the selected bits do not match the legal values;

said rejection device is further configured to reject the incoming transmission if the packet reject line is asserted;

said state machine is coupled to the incoming transmission and the packet reject line and configured to produce at least a part of a timing of a channel busy signal based on the incoming transmission and the packet reject line;

the device further comprising a transmitter coupled to the channel busy signal;

said transmitter is configured to allow transmissions based on the channel busy signal;

said receiver is coupled to the packet reject line;

said receiver is further configured to reset based on assertion of the packet reject line;

said state machine is further configured to assert the channel busy signal when the receiver receives the incoming transmission and clear the channel busy line when the incoming transmission is rejected;

said legal values comprise a predetermined value and a range of values for data rate bits, reserved bits, length bits, and service field bits;

the device further comprising memory elements configured to store the selected bits;

said comparator comprises,

a register configured to store the legal values, and

a logic device configured to compare stored values in the register to stored values in the memory elements;

the comparison device is coupled to each memory element and each register location in the register;

said bit slice recognizer is configured to recognize data rate bits, reserved bits, length bits, service field bits, and other predetermined bits in a packet of the incoming transmission;

the device further comprising a demodulator configured to demodulate the received transmissions;

said demodulator coupled to the packet reject line and further configured to reset if the packet reject line is asserted;

the device further comprising an input mechanism configured to write the legal values in said register;

said input mechanism includes software configured to query a user for the legal values and software to write the legal values to said register; and

at least some of the legal values are written to said register in tabular format.