The concern is that during transmission, a 1 bit will be converted to a 0 bit or vice versa, thus destroying the bit structure integrity of the character. In other words, the original character is incorrectly presented as a different yet valid character. Errors of this sort, if undetected, could alter financial numbers. A parity check can detect errors at the receiving end. The system again counts the 1 bits, which should always equal an odd number of 1 bits for the character will be even, which would signal an error.
The problem with using vertical parity alone is the possibility that an error will change two bits in the structure simultaneously, thus retaining the parity of the character. In fact, some estimates indicate a 40 to 50 percent chance that line noise will corrupt more than one bit within a character. Using horizontal parity in conjunction with vertical parity reduces this problem. In Figure 3.8, notice the parity bit following each block of characters. The combination of vertical and horizontal parity provides a higher degree of protection from line errors.
Audit Objectives Relating to Equipment Failure
The auditor’s objective is to verify the integrity of the electronic commerce transactions by determining that control are in place to detect and correct message loss due to equipment failure.
Audit Procedures Relating to Equipment Failure
To achieve this control objective, the auditor can select a sample of message from the transaction log and examine them for garbled content caused by line noise. The auditor should verify that all corrupted message were successfully retransmitted.