Communication method, apparatus, and system

1 . A method comprising:

sending a first bit sequence having a length of N 1 bits to a first device, wherein the first bit sequence comprises P subsequences, each referred to as a subsequence A, and having a length of N 1 /P bits, wherein each of the P subsequences A comprises one or more first forward error correction (FEC) code blocks, and wherein P is a positive integer;

obtaining a quantity of abnormal bits in the first bit sequence;

obtaining a first bit error rate (BER) based on the quantity of abnormal bits in the first bit sequence;

sending a second bit sequence having a length of N 2 bits to the first device, wherein the second bit sequence comprises Q subsequences, each referred to as a subsequence B, and having a length of N 2 /Q bits, wherein N 2 is greater than or equal to N 1 , wherein each of the Q subsequences B comprises one or more second FEC code blocks, wherein Q is a positive integer;

obtaining a quantity of abnormal bits in the second bit sequence;

obtaining a second BER based on the quantity of abnormal bits in the second bit sequence; and

outputting the first BER and the second BER.

2 . The method of claim 1 , further comprising sending the second bit sequence to the first device when the first BER equals or exceeds a first preset BER threshold.

3 . The method of claim 2 , wherein the one or more FEC code blocks consist of X third FEC code blocks and Y fourth FEC code blocks, wherein all first bits in a first data element sequence of each of the X third FEC code blocks are normal bits, wherein a second data element sequence of each of the Y fourth FEC code blocks comprises abnormal bits of a fixed quantity or abnormal bits of a fixed proportion, wherein Y or a ratio of Y to (X+Y) corresponds to the first preset BER threshold, and wherein X and Y are positive integers.

4 . The method of claim 3 , wherein all bits in the second data element sequence of each of the Y fourth FEC code blocks are abnormal bits.

5 . A method comprising:

receiving a first bit sequence having a length of N 1 bits from a first device, wherein the first bit sequence comprises P subsequences, each referred to as a subsequence A, and having a length of N 1 /P bits, wherein each of the P subsequences A comprises one or more first forward error correction (FEC) code blocks, and wherein P is a positive integer;

obtaining a quantity of abnormal bits in the first bit sequence;

obtaining a first bit error rate (BER) based on the quantity of abnormal bits in the first bit sequence;

receiving a second bit sequence having a length of N 2 bits from the first device, wherein the second bit sequence comprises Q subsequences, each referred to as a subsequence B, and having a length of N 2 /Q bits, wherein N 2 is greater than or equal to N 1 , wherein each of the Q subsequences B comprises one or more second FEC code blocks, and wherein Q is a positive integer;

obtaining a quantity of abnormal bits in the second bit sequence;

obtaining a second BER based on the quantity of abnormal bits in the second bit sequence; and

outputting the first BER and the second BER.

6 . The method of claim 5 , further comprising obtaining the second BER when the first BER equals or exceeds a first preset BER threshold.

7 . The method of claim 6 , wherein the one or more first and second FEC code blocks consist of X third FEC code blocks and Y fourth FEC code blocks, wherein all first bits in a first data element sequence of each of the X third FEC code blocks are normal bits, wherein a second data element sequence of each of the Y fourth FEC code blocks comprises abnormal bits of a fixed quantity or abnormal bits of a fixed proportion, wherein Y or a ratio of Y to (X+Y) corresponds to the first preset BER threshold, and wherein X and Y are positive integers.

8 . The method of claim 7 , wherein all bits in the second data element sequence of each of the Y fourth FEC code blocks are abnormal bits.

9 . The method of claim 5 , wherein a length of each of the P subsequences A is equal to a length of each of the Q subsequences B.

10 . The method of claim 5 , wherein 1 is a first value of an abnormal bit when a second value of a normal bit is 0, and wherein 0 is the first value when the second value is 1.

11 . The method of claim 10 , wherein the second value is 0, wherein all bits in the one or more first FEC code blocks are 0, wherein all abnormal bits of a fixed quantity or a fixed proportion in the one or more second FEC code blocks are 1, and wherein all remaining bits in the one or more second FEC code blocks are 0.

12 . The method of claim 5 , wherein before receiving the first bit sequence, the method further comprises performing link training with the first device.

13 . A test equipment comprising:

a memory configured to store instructions; and

at least one processor coupled to the memory and configured to execute the instructions to cause the test equipment to:

send a first bit sequence having a length of N 1 bits to a first device, wherein the first bit sequence comprises P subsequences, each referred to as a subsequence A, and having a length of N 1 /P bits, wherein each of the P subsequences A comprises one or more first forward error correction (FEC) code blocks, and wherein P is a positive integer;

obtain a quantity of abnormal bits in the first bit sequence;

obtain a first bit error rate (BER) based on the quantity of abnormal bits in the first bit sequence;

send a second bit sequence having a length of N 2 bits to the first device, wherein the second bit sequence comprises Q subsequences, each referred to as a subsequence B, and having a length of N 2 /Q bits, wherein N 2 is greater than or equal to N 1 , wherein each of the Q subsequences B comprises one or more second FEC code blocks, wherein Q is a positive integer;

obtain a quantity of abnormal bits in the second bit sequence;

obtain a second BER based on the quantity of abnormal bits in the second bit sequence; and

output the first BER and the second BER.

14 . The test equipment of claim 13 , wherein the at least one processor is further configured to execute the instructions to cause the test equipment to send the second bit sequence to the first device when the first BER equals or exceeds a first preset BER threshold.

15 . The test equipment of claim 14 , wherein the one or more FEC code blocks consist of X third FEC code blocks and Y fourth FEC code blocks, wherein all first bits in a first data element sequence of each of the X third FEC code blocks are normal bits, wherein a second data element sequence of each of the fourth FEC code blocks comprises abnormal bits of a fixed quantity or abnormal bits of a fixed proportion, wherein Y or a ratio of Y to (X+Y) corresponds to the first preset BER threshold, and wherein X and Y are positive integers.

16 . The test equipment of claim 15 , wherein all bits in the second data element sequence of each of the Y fourth FEC code blocks are abnormal bits.

17 . The test equipment of claim 13 , wherein a length of each of the P subsequences A is equal to a length of each of the Q subsequences B.

18 . The test equipment of claim 13 , wherein 1 is a first value of an abnormal bit when a second value of a normal bit is 0; and wherein 0 is the first value when the second value is 1.

19 . The test equipment of claim 18 , wherein the second value is 0, wherein all bits in the one or more first FEC code blocks are 0, wherein all abnormal bits of a fixed quantity or a fixed proportion in the one or more second FEC code blocks are 1, and wherein all remaining bits in the one or more second FEC code blocks are 0.

20 . The test equipment of claim 13 , wherein the at least one processor is further configured to execute the instructions to cause the test equipment to perform link training with the first device.