The numerical count position of a specific security segment that is within the actual received security header/trailer segment group pair, identified by its security reference number. The numbering starts with, and includes, the USH segment as segment number 1. To identify a security segment that contains an error, this is the numerical count position of that security segment. To report that a security segment is missing, this is the numerical count position of the last security segment that was processed before the position where the missing security segment was expected to be. A missing security segment group is denoted by identifying the first segment in the security segment group as missing.