The money transfer between customers' accounts consists of two steps: The communication of the transaction records (who to debit or credit and what to print on

The money transfer between customers' accounts consists of two steps: The communication of the transaction records (who to debit or credit and what to print on their statement) and the settlement of the resulting total money transfer between the banks. The latter is what usually happens through the central bank, where both banks have accounts that are used to settle the total of all money movements between the two banks within a given period, in a single transaction between the two accounts. The transmission of the transaction records is independent from that and can happen in any way the banks see fit, including SWIFT (and sometimes the central bank, if it offers that service).