ISO 8583

ISO 8583 is an international standard for financial transaction card originated interchange messaging. It is the International Organization for Standardization standard for systems that exchange electronic transactions initiated by cardholders using payment cards.

ISO 8583 defines a message format and a communication flow so that different systems can exchange these transaction requests and responses. The vast majority of transactions made when a customer uses a card to make a payment in a store (EFTPOS) use ISO 8583 at some point in the communication chain, as do transactions made at ATMs. In particular, the MasterCard, Visa and Verve networks base their authorization communications on the ISO 8583 standard, as do many other institutions and networks.

Message format

An ISO 8583 message is made of the following parts:

• Message type indicator (MTI)
• One or more bitmaps, indicating which data elements are present
• Data elements, the actual information fields of the message

Message type indicator (MTI)

The first digit of the MTI indicates the ISO 8583 version in which the message is encoded

Position two of the MTI specifies the overall purpose of the message.Position two of the MTI specifies the overall purpose of the message.

Position three of the MTI specifies the message function which defines how the message should flow within the system. Requests are end-to-end messages (e.g., from acquirer to issuer and back with time-outs and automatic reversals in place), while advices are point-to-point messages (e.g., from terminal to acquirer, from acquirer to network, from network to issuer, with transmission guaranteed over each link, but not necessarily immediately).

Position four of the MTI defines the location of the message source within the payment chain.