[RQ7.16] SPDU_ID_1, SPDU_ID_2 and SPDU_ID_3 shall be calculated according to Figure 21 and Table 36.

Figure 21 – Calculation of the SPDU_ID

Table 36 – Presentation of the SPDU_ID

SPDU_ID_1:= SafetyBaseID (octets 0…3) XOR SafetyProviderLevel_ID (octets 0…3)

SPDU_ID_2:= SafetyBaseID (octets 4…7) XOR SafetyStructureSignature (octets 0…3)

SPDU_ID_3:= SafetyBaseID (octets 8…11) XOR SafetyBaseID (octets 12…15) XOR SafetyProviderID (octets 0…3)

In case of a mismatch between expected SPDU_ID and actual SPDU_ID, the following rules can be used for diagnostic purposes:

• If all of SPDU_ID_1, SPDU_ID_2, and SPDU_ID_3 differ, there probably is a mismatching SafetyBaseID.
• If SPDU_ID_3 differs, but SPDU_ID_1 and SPDU_ID_2 do not, there is a mismatching SafetyProviderID.
• If SPDU_ID_2 differs, but SPDU_ID_1 and SPDU_ID_3 do not, the structure or identifier of the SafetyData do not match.
• If SPDU_ID_1 differs, but SPDU_ID_2 and SPDU_ID_3 do not, the SafetyProviderLevel does not match.

By these rules, there is a very low probability (<10-9) that a mismatching SafetyBaseID will be misinterpreted. From a practical view, this probability can be ignored.