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ISO 8583 is an international standard for financial transaction card originated interchange messaging. It defines a message format and a communication flow so that different systems can exchange transaction requests and responses. This standard is widely used in electronic transactions initiated by cardholders using payment cards, such as those made at point-of-sale (POS) terminals and automated teller machines (ATMs).
Message Type Indicator (MTI)
The Message Type Indicator (MTI) is a four-digit numeric field that indicates the overall function of the message. The MTI includes the ISO 8583 version, the Message Class, the Message Function, and the Message Origin.
ISO 8583 Version
The first digit of the MTI indicates the ISO 8583 version in which the message is encoded:
- 0xxx: ISO 8583:1987
- 1xxx: ISO 8583:1993
- 2xxx: ISO 8583:2003
- 3xxx: Reserved by ISO
- 8xxx: National use
- 9xxx: Private use
Message Class
The second digit specifies the overall purpose of the message:
- x1xx: Authorization message
- x2xx: Financial messages
- x3xx: File actions message
- x4xx: Reversal and charge-back messages
- x5xx: Reconciliation message
- x6xx: Administrative message
- x7xx: Fee collection messages
- x8xx: Network management message
Message Function
The third digit specifies the message function, defining how the message should flow within the system:
- xx0x: Request
- xx1x: Request response
- xx2x: Advice
- xx3x: Advice response
- xx4x: Notification
- xx5x: Notification acknowledgement
- xx6x: Instruction
- xx7x: Instruction acknowledgement
Message Origin
The fourth digit defines the location of the message source within the payment chain:
- xxx0: Acquirer
- xxx1: Acquirer repeat
- xxx2: Issuer
- xxx3: Issuer repeat
- xxx4: Other
Examples of MTI Values
Here are some examples of MTI values and their meanings:
- 0100: Authorization Request – Request from a POS terminal for authorization for a cardholder purchase.
- 0110: Authorization Response – Response to a POS terminal for authorization for a cardholder purchase.
- 0200: Acquirer Financial Request – Request for funds, typically from an ATM or POS device.
- 0210: Issuer Response to Financial Request – Issuer response to request for funds.
- 0400: Acquirer Reversal Request – Reverses a transaction.
- 0800: Network Management Request – Hypercom terminals initialize request, echo test, logon, logoff, etc.
Bitmaps and Data Elements
In ISO 8583, a bitmap is a field within a message that indicates whether other data elements are present. A message will contain at least one primary bitmap, which indicates whether data elements 1 to 64 are present. If a secondary bitmap is present, it indicates whether data elements 65 to 128 are present.
Data elements are the individual fields carrying the transaction information. There are up to 128 data elements specified in the original ISO 8583:1987 standard, and up to 192 data elements in later releases. Each data element has a specified meaning and format, such as numeric, alphanumeric, or binary.
By understanding the structure and components of ISO 8583 messages, financial institutions can ensure seamless communication and interoperability between different systems and networks.