Detecting bit errors in a communications system
Error codes output from a serializer/deserializer in a node of a communications network are detected by error decode logic that assumes that each new error occurrence reflects a one bit error in the word giving rise to the error code. Each error occurrence is then counted. When the error count reaches a predetermined limit (e.g., 250 errors), the total bit count required to accumulate the 250 errors is then determined. The total bits can be determined based on a clock count (time). The BER is then calculated based upon the fixed error limit and the total bit count. This BER is then reported and used to determine the health of the network.
1. A technique for determining a bit error rate comprising:
receiving a digital signal;
resetting an error counter and starting a time counter;
detecting errors in said digital signal, wherein said error counter is updated for each error detected;
determining when said errors counter reaches a predetermined threshold;
stopping the time counter when said errors counter reaches said predetermined threshold; and
calculating a bit error rate based upon said predetermined threshold and a value of the time counter.
2. The method of claim 1 further comprising:
determining a value corresponding to the number of bits received during the time it took for said errors to reach said threshold; and
calculating said bit error rate based on said threshold and said value.
3. The method of claim 1 wherein said digital signal is a serial data stream and wherein said detecting errors comprises detecting errors by a deserializer that converts incoming serial-bit words to parallel-bit words.
4. The method of claim 3 wherein said deserializer converts a serial 10 bit word to a parallel 8 bit word.
5. The method of claim 3 wherein said deserializer performs the method of detecting positive and negative disparities of said serial-bit words and generating a disparity error signal if a disparity is inconsistent with a predetermined data format.
6. The method of claim 1 wherein said detecting errors comprises determining errors based upon whether a disparity of an incoming digital word is not of a predicted disparity.
7. The method of claim 1 wherein said detecting errors comprises determining whether a received digital word meets a requirement for an acceptable word.
8. The method of claim 1 wherein said detecting errors comprises determining a loss of synchronization.
9. The method of claim 1 wherein said detecting errors comprises detecting at least out-of-band errors, disparity errors, and loss of synchronization.
10. The method of claim 9 wherein each of said out-of-band errors, disparity errors, and loss of synchronization errors is treated as a single bit error.
11. The method of claim 1 wherein said predetermined threshold is between 100–1000 bit errors.
12. The method of claim 1 wherein said predetermined threshold is 250 bit errors.
13. A circuit for determining a bit error rate comprising:
a receiver for receiving digital information and determining whether said information contains errors;
an error counter for counting errors;
a count detector connected to an output of said error counter for detecting when said error counter reaches a predetermined error threshold value;
a clock cycle counter for storing a value corresponding to a time from when said error counter is reset to when said error counter to reaches said predetermined error threshold value; and
a processing circuit for calculating a bit error rate based upon said threshold and said value.
14. The circuit of claim 13 wherein said receiver is a serializer/deserializer.
15. The circuit of claim 14 wherein said serializer/deserializer is a model VSC7216 serializer/deserializer.
16. The circuit of claim 13 further comprising a word clock providing clock signals to said error counter and said clock cycle counter.
17. The circuit of claim 13 wherein said circuit is part of a Gigabit Ethernet.
18. The circuit of claim 13 wherein said error counter wraps around when said error counter reaches said threshold.
19. The circuit of claim 13 wherein said processing circuit resets said error counter and said clock cycle counter after reading values output by said error counter and said clock cycle counter.
20. The circuit of claim 13 wherein said threshold is between 100–1000 errors.
21. The circuit of claim 13 wherein said threshold is 250 errors.