Single Message System
Mastercard offers merchants two ways to process payment card transactions. With the single message system, authorization, clearing, and settlement occur in a single message.
The single message system is most commonly used for transactions with a PIN confirmation, such as card-present and ATM transactions.
The single message system differs from the dual message system which sends an authorization request with the first message and requests settlement with the second message.
The dual message system is most commonly used for transactions with signature confirmation, both physical signatures for card-present transactions and electronic signatures for card-not-present transactions.