Networking device and method for making cyclic redundancy check (CRC) immune to scrambler error duplication

• US 6,609,226 B1
• Filed: 04/10/2000
• Issued: 08/19/2003
• Est. Priority Date: 04/10/2000
• Status: Expired due to Term

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Figueira, Norival R.
• Primary Examiner(s): Baker, Stephen M.
• Application Number:
  US09/545,660
• Time in Patent Office: 1,226 Days
• Field of Search: 714/798, 714/807
• US Class Current: 714/807
• CPC Class Codes: H03M 13/093 CRC update after modification of the information word
• CPC Class Codes: H04L 1/0061 Error detection codes
• CPC Class Codes: H04L 1/0083 Formatting with frames or packets; Protocol or part of protocol for error control

Abstract

A networking device and method for transparently modifying a cyclic redundancy check (CRC) of a message so that higher layers (e.g., data link layer and above) can detect error duplication caused by scrambling and descrambling. No increase in the size of the messaging is needed so that the invention may be used for current and future technologies. In one embodiment, the networking device comprises logic employed within a physical layer of the device. This logic, referred to as a scrambler, modifies an original cyclic redundancy check (CRC) value associated with a message. This enables detection of a duplication of bit errors at a targeted destination of the message.

Claims

1. A networking device comprising logic employed within a physical layer of the device to modify an original cyclic redundancy check (CRC) value associated with a message and enable detection of a duplication of bit errors at a targeted destination of the message, the logic comprises a scrambler that comprises (1) a CRC engine to calculate a value based on a bit sequence including a state of the scrambler prior to scrambling a body of the message and a plurality of zero bits equal in number to a bit size of the message, and (2) an adder to perform modulo 2 addition on the value and the original CRC value of the message to produce a modified CRC value.

2. The networking device of claim 1, wherein the duplication of bit errors is caused by bit errors occurring a predetermined number of bits before a beginning of the message.

3. The networking device of claim 1 further comprising a data link layer in communication with the physical layer.

4. The networking device of claim 3, wherein the modification of the CRC value is transparent to the data link layer.

5. The networking device of claim 4, wherein a format of the transmitted message remains unmodified even after modification of the CRC value.

6. A networking device comprising logic employed within a physical layer of the device to modify an original cyclic redundancy check (CRC) value associated with a message and enable detection of a duplication of bit errors at a targeted destination of the message, the logic is a x^N+1 scrambler, where N being a positive whole number, including

a CRC engine to calculate a resulting CRC value based on a bit sequence including a state of the x^N+1 scrambler after a last bit of a body of the message has been scrambled;

a table to produce an inverse value to the resulting CRC value;

an adder to perform modulo 2 addition on the inverse value and a bit pattern from a selected portion of the message having a least significant bit N bits away from a least significant bit of the message.

7. The networking device of claim 6, wherein the duplication of bit errors is caused by bit errors occurring a predetermined number of bits after an ending of the message.

8. A networking device comprising:

a data link layer; and

a physical layer including a descrambler to perform operations on a message transparent to the data link layer to enable the data link layer to detect a duplication of bit errors caused by scrambling of information within a body of the message prior to receipt of the message, the descrambler includes

a CRC engine to calculate a value based on a bit sequence including a state of the descrambler prior to descrambling of the body of the message and a plurality of zero bits equal in number to a bit size of the message, and

an adder to perform modulo 2 addition on the value and a modified CRC value contained in the message to produce an original CRC value of the message.

9. The networking device of claim 8, wherein a format of the received message remains intact even after descrambling the body of the message.

10. The networking device of claim 8, wherein the duplication of bit errors is caused by bit errors occurring a predetermined number of bits before a beginning of the message.

11. A networking device comprising:

a data link layer; and

a physical layer including a descrambler to perform operations on a message transparent to the data link layer to enable the data link layer to detect a duplication of bit errors caused by scrambling of information within a body of the message prior to receipt of the message, the descrambler is a x^N+1 descrambler, where N being a positive whole number, that comprises

a CRC engine to calculate a resulting CRC value based on a bit sequence including a state of the x^N+1 scrambler after a last bit of a body of the message has been descrambled;

a table to produce an inverse value to the resulting CRC value;

a first adder to perform modulo 2 addition on the inverse value and a bit pattern from a selected portion of the message having a least significant bit N bits way from a least significant bit of the message; and

a second adder to perform modulo 2 addition on the inverse value and a modified CRC value contained in the message.

12. The networking device of claim 11, wherein the duplication of bit errors is caused by bit errors occurring a predetermined number of bits after an ending of the message.

13. The networking device of claim 12, wherein the descrambler is a x^N+1 descrambler, where N being a positive whole number.

14. A network comprising:

a first networking device including a scrambler employed within a physical layer of the first networking device that only modifies an original cyclic redundancy check (CRC) value of a message prior to scrambling of a body of the message before transmission; and

a second networking device in communication with the first networking device, the second networking device including a descrambler employed within a physical layer of the second networking device to perform descrambling operations on the body of the message and subsequently modifying the CRC value based on a bit sequence including a state of the descrambler just prior to descrambling of the body of the message and a plurality of zero bits equal in number to a bit size of the message.

15. A method comprising:

loading a bit sequence to act as coefficients of a polynomial into a cyclic redundancy check (CRC) engine, the bit sequence including a state of a scrambler at a moment that a first bit of a transmitted message is to be scrambled and a number of zero bits equal in size to a number of bits contained in the transmitted message;

calculate a first resulting CRC value; and

performing arithmetic computations on the first resulting CRC value and an original CRC value to produce a modified CRC value.

16. The method of claim 15, wherein the arithmetic computations includes modulo 2 addition.

17. The method of claim 15, further comprising:

loading a bit sequence to act as coefficients of a polynomial into a cyclic redundancy check (CRC) engine, the bit sequence including a state of a descrambler at a moment that a first bit of the transmitted message is to be descrambled and a number of zero bits equal in size to a number of bits contained in the transmitted message;

calculate a second resulting CRC value; and

performing modulo 2 addition on the second resulting CRC value and the modified CRC value.

18. A program loaded in memory of a networking device for execution therein, the program comprising a scrambler being code to modify an original cyclic redundancy check (CRC) value of a message through modulo 2 addition prior to scrambling of a body of the message before transmission.

19. The program of claim 18 further comprising:

a descrambler being code to perform descrambling operations on a body of an incoming message and subsequently modifying a CRC value of the message based on a bit sequence including a state of the descrambler just prior to descrambling of the body of the message and a plurality of zero bits equal in number to a bit size of the message.