What is MTI (Message type indicator) in ISO-8583 message ?

An ISO 8583 message is made of the following parts :

 1. Message type indicator (MTI)

 2. One or more bitmaps, indicating which data elements are present.

 3. Data elements, the fields of the message

MTI (Message type indicator)

This is a 4 digit numeric field which classifies the high level function of the message.

A message type indicator includes the ISO 8583 version, the Message Class, the Message Function and the Message Origin.

0xxx  Version of ISO 8583 (1987 version)

x1xx  Class of the message (Authorization Message)

xx1x  Function of the message (Request Response)

xxx0  who began the communication (Acquirer)

MTI version

Position one of the MTI specifies the versions of the ISO 8583 standard which is being used to transmit the message.

0xxx  ISO 8583-1:1987 version

1xxx  ISO 8583-2:1993 version

2xxx  ISO 8583-1:2003 version

9xxx  Private usage

Message class

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

x1xx  Authorization message

x2xx  Financial message

x3xx  File Actions message (used for hot-card, TMS and other exchanges)

x4xx  Reversal message (Reverses the action of a previous authorization)

x5xx  Reconciliation Message (Transmits settlement information)

x6xx  Administrative Message (Transmits administrative advice. Often used for message reject or failure to apply)

x7xx  Fee Collection Message

x8xx  Network Management Message (used for secure key exchange, logon, echo test and other network functions)

x9xx  Reserved by ISO

Message function

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 timeouts and automatic reversals in place)

Advices are point-to-point messages (e.g., from terminal to acquirer, from acquirer to network, from network to issuer.

xx0x  Request

xx1x  Request Response

xx2x  Advice

xx3x  Advice Response

xx4x  Notification

xx8x  Response acknowledgment

xx9x  Negative acknowledgment

Message origin

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

xxx0  Acquirer

xxx1  Acquirer Repeat

xxx2  Issuer

xxx3  Issuer Repeat

xxx4  Other

xxx5  Other Repeat

Bearing each of the above four positions in mind, an MTI will completely specify what a message should do, and how it is to be transmitted around the network.