In order to allow a terminal to be able to support multiple card schemes, it is necessary for the EMV kernel being used to perform some common Application Selection and Kernel Activation processing to enable it to determine the applicable scheme rules that should be applied – this is known as Entry Point processing. There are multiple sub processes within Entry Point processing, including the following:
The four start conditions A to D mark the different ways in which the Entry Point can begin a transaction. Typically Start A is how a new transaction will commence, whereas Starts B to D are generally triggered by a previous transaction ending in an incomplete way.
In the cases of Start C or Start D, Entry Point Pre-Processing indicators will be retained and provided between transactions.
Start A is used in most acceptance environments at the initiation of a new transaction and enters the transaction at the Pre-Processing stage, subsequently going through all the other processing stages.
Start B bypasses the Pre-Processing stage and moves straight to Protocol Activation.
This may be possible when the transaction amounts are fixed and so Pre-Processing is not necessary (for example a parking lot with a single fixed price tariff, and where Mag-Stripe Mode is the only supported mode).
Another scenario where Start B may be used is if a card needs to be re-presented. For example, if CDCVM is required and the cardholder has not yet performed it then Start B might be used after the cardholder has been asked to follow the instructions on their consumer device and re-present it to the terminal.
Start C begins the transaction at the Combination Selection stage and is typically only used when it was not possible to process a transaction using a previously selected combination, for example if any of the transaction parameters were not supported by that card application. If there is at least one remaining combination that has not yet been attempted, then the kernel will select the highest priority remaining combination and will proceed with activation of the appropriate kernel. This process could potentially be repeated until all combinations have been attempted.
Start D is used to resume the processing of a specific kernel that was previously activated during the transaction. This may be used for risk management purposes in situations where the Entry Point restarts mid-transaction, for example after an online authorisation was attempted.