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CAN bus CRC - Probability of Undetected Failure

William Glover

I wonder if anyone could help me please.

I am writing an assessment of the safety implications of functions that are reliant on a CAN bus.  

More specifically, I am interested in the Probability of Undetected Failure of the CAN bus CRC-15 Cyclic Redundancy Check.  I have found some figures and graphs for some specific CRCs, for some Bit Error Ratios, but not for the specific CRC of interest.  I know there are ways of calculating these figures given the CRC polynomial, packet length, and BER, but in the papers I have seen, the maths looks a bit beyond me.  Also, as it is a commonly used CRC I am interested in, I was hoping to find a source of pre-calculated values, ideally for a range of BERs.

Any assistance or guidance would be appreciated. 

Thanks

Bill

Parents
  • 0

    I am afraid the description is too vague for me to help, although you hint at specificity. The manufacturer of the kit would be the obvious body to ask. Otherwise some user group such as CiA https://www.can-cia.org/about-us/ 

  • 0 in reply to Peter Bernard Ladkin

    Hi Peter

    Thanks for your response to my query.  I must apologise for the delay in my response.

    For various reasons, I am unable to expand on the details of the system I am dealing with, which is why the original question is deliberately vague about the application.

    The system I am dealing with is fully developed and in trials.  Some of the CAN network nodes in the system were developed by my company, some by sub-contractors to our main customer, and some are supplied by the ultimate end user for the system.  It will not be possible to get detailed technical information about all of the nodes to support my safety case.  However, that is not germane to my question.

    Regardless of the safety integrity to which the network nodes were developed, there is still a possibility that a frame on the CAN bus could be corrupted in transmission in such a way that the CRC does not detect it.  Our customer has asked us very specifically to include that failure in our safety case.  This will involve including the failure “message corruption in transmission, undetected by CRC” in a Fault Tree.  I therefore need to assign a probability to that failure.  This is why my question is very focused on the probability of undetected failure of the CAN 15-bit CRC, and not on any other failure mode of the network, as those other modes are accounted for elsewhere.

    I can find information on the probability of undetected failures for some other CRCs, dependent on packet length and BER, but I can’t file this information for the CAN 15-bit CRC.

     If you could provide this specific information, or any pointers to where I should look next, I would really appreciate it.

    Best Regards

    Bill

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  • 0 in reply to Peter Bernard Ladkin

    Hi Peter

    Thanks for your response to my query.  I must apologise for the delay in my response.

    For various reasons, I am unable to expand on the details of the system I am dealing with, which is why the original question is deliberately vague about the application.

    The system I am dealing with is fully developed and in trials.  Some of the CAN network nodes in the system were developed by my company, some by sub-contractors to our main customer, and some are supplied by the ultimate end user for the system.  It will not be possible to get detailed technical information about all of the nodes to support my safety case.  However, that is not germane to my question.

    Regardless of the safety integrity to which the network nodes were developed, there is still a possibility that a frame on the CAN bus could be corrupted in transmission in such a way that the CRC does not detect it.  Our customer has asked us very specifically to include that failure in our safety case.  This will involve including the failure “message corruption in transmission, undetected by CRC” in a Fault Tree.  I therefore need to assign a probability to that failure.  This is why my question is very focused on the probability of undetected failure of the CAN 15-bit CRC, and not on any other failure mode of the network, as those other modes are accounted for elsewhere.

    I can find information on the probability of undetected failures for some other CRCs, dependent on packet length and BER, but I can’t file this information for the CAN 15-bit CRC.

     If you could provide this specific information, or any pointers to where I should look next, I would really appreciate it.

    Best Regards

    Bill

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  • 0 in reply to William Glover

    The guy who convenes the German safety-standards committee for reliable/safe communication networks is a close colleague of mine, a former full-time academic who prefers to work in industry (although he still has a part-time academic position). I'll ask. He is off work at the moment until later in the week.

  • 0 in reply to Peter Bernard Ladkin

    Hi Peter

    Thanks for your swift response.  That would be great, thanks.

    Bill

  • 0 in reply to William Glover

    The response from Frank.  

    [begin quote]

    The official CAN group is here: https://www.can-cia.org/

    They should give the information needed.

    If the polynomial is proper then the max Residual Error Probability is 2^-15.

    I can calculate it for a specific data length but he might need an official value.

    Below are all values for data lengths between 1 and 800 bits. [pic omitted here]

    They probably have used a small bit error probability and a kind of data redundancy additionally. I remember, I tried to get some specific information about 15 years ago and gave up quickly since it was not important at all to me at that time.

    I use CAN as an example for Res. Err. Prob. only.

    [end quote]

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