ISO8583 flows, fields meaning and values

This tutorial will present message flows, data elements values and meanings. To get more information on ISO8583 message format follow Introduction to ISO8583 financial transaction message format tutorial.

Introduction

If we imagine a generic message flow between 2 institutions regardless the scope, this can be captured in the following diagram.

Message Flows

Bellow is a list with most used message types.

• X100/X101 - Authorization message
• X200/X201 - Financial presentment message
• X220/X221 - Financial accumulation presentment message
• X300/X301 - File action message
• X400/X401 - Reversal message
• X420/X421 - Reversal advice message
• X500/X501 - Reconciliation message
• X600/X601 - Administrative message
• X800/X801 - Network management message

X100/X101 - Authorization message

An authorization message is an approval or guarantee of funds given by the card issuer to the acquirer.

X200/X201 - Financial presentment message

A financial presentment message can be used as a complete transaction: to transfer the money from one account to another.

X220/X221 - Financial accumulation presentment message

A financial accumulation presentment message completes the transactions, usually used in combination with an x100 message.

X300/X301 - File action message

A file action message is used to add, change, delete or replace a file or record or inquire into a file or perform card administration.

X400/X401 - Reversal message

A reversal message is the partial or complete cancellation of the effects of a previous authorization (x100), financial transaction (x200), or financial transaction advice (x220) that cannot be processed as instructed.

X420/X421 - Reversal advice message

A reversal advice message is a notification that the initial transaction failed. This can be an authorization (x100) or financial transaction (x200).

X500/X501 - Reconciliation message

A reconciliation message is the exchange of totals between two institutions. e.g. sent at the end of the day.

X600/X601 - Administrative message

Can any message related to the technical infrastructure between financial institutions.

X800/X801 - Network management message

Network management contains a large range of messages, like:

• system initialization or shutdown;
• system security management, e.g. sending automatical key changes;
• system audit controls;

Examples

Lets take 2 real examples of iso8583 flows usage.

Top-up a mobile phone

Let's say we have a system that can accept credit/debit cards to top-up a mobile phone. This can be done if the following steps:

• x100 message to the bank to authorise the transaction and verify the amount availability;
• x200 message to the mobile phone company to increase the phone account balance.
• x220 to the bank to complete the transaction, or x420 to the bank to cancel the authorisation if the x200 failed.

ATM

Let's imagine an ATM day:

• ATM receives x800 to start;
• ATM send x800 request the encryption key (master key exchange);
• ATM send x100 messages during the day for balance inquiry;
• ATM send x200 messages during the day for cash withdraw;
• ATM receive x600 from bank to check the total cash amount available.
• ATM send x500 reconciliation message at the end of the day with daily activity.

Data elements

Depends on the message scope, some of the data elements are used more than the others. Here is a list of some of the most used data elements and the possible values.

• Field 2 - Primary account number
• Field 3 - Processing code
• Field 4 - Amount transaction
• Field 7 - Transmission date & time
• Field 11 - System trace audit number (STAN)
• Field 12 - Time, local transaction (hhmmss)
• Field 13 - Date, local transaction (MMDD)
• Field 22 - Point of service entry mode
• Field 37 - Retrieval reference number
• Field 39 - Response code
• Field 41 - Card acceptor terminal identification
• Field 42 - Card acceptor identification code
• Field 43 - Card acceptor name/location
• Field 49 - Currency code, Transaction

Field 2 - Primary account number

A number identifying the cardholder and the card issuer. If the field is missing and the message contains data element 35, the PAN can be read from there.

The primary account number is composed of:

• Issuer Identification Number (IIN), first 6 digits;
• a variable length (up to 12 digits) individual account identifier;
• a single check digit calculated using the Luhn algorithm.

Field 3 - Processing code

The Processing code is a constructed data element and is composed of 3 fields:

• Transaction type code, an 2 - describes the specific transaction type;
• Account type code 1, an 2 - describes the account type affected for debits ("from");
• Account type code 2, an 2 - describes the account type affected for credits ("to").

Transaction type values:

Account type values:

Field 4 - Amount transaction

The amount transaction field represents the funds requested by the cardholder in the local currency (field 49).

Field 7 - Transmission date & time

Contains the date and time the message initiator sends this message expressed in UTC (MMDDhhmmss).

Field 11 - System trace audit number (STAN)

A number assigned by a transaction originator to assist in identifying a transaction uniquely. The systems trace audit number remains unchanged for all messages within a transaction.

Field 12 - Time, local transaction (hhmmss)

Contains the time local transaction in hhmmss format providing the time when the transaction takes place at the card acceptor location.

Field 13 - Date, local transaction (MMDD)

Contains the date local transaction in MMDD format providing the date when the transaction takes place at the card acceptor location.

Field 22 - Point of service entry mode

POS entry mode field is a constructed data element (field) and is used to capture the account number and pin capture capability of the terminal:

• PAN entry mode, digit 1-2
• PIN entry capability digit 3.

PAN entry mode

PIN entry capability

Field 37 - Retrieval reference number

An alphanumeric code assigned to a transaction in order to uniquely identify a transaction. This code remains unchanged throughout the life of the transaction.

Field 39 - Response code

Response Code used to indicate whether the transaction is approved or declined.

Field 41 - Card acceptor terminal identification

A unique code identifying a terminal at the card acceptor location. This code is also referred to as the Terminal Identifier or 'TID.'

Field 42 - Card acceptor identification code

A code identifying the merchant. This code is also referred to as the Merchant Identifier or 'MID.'

Field 43 - Card acceptor name/location

The name and location of the card acceptor. This is a composed field:

• 1-23: address;
• 24-36: city;
• 37-38: state;
• 39-40: country.

Field 49 - Currency Code, Transaction

The local currency of the acquirer or source location of the transaction. The field can contain both alphanumeric or numeric code from ISO 4217 standard. e.g. USD or 840.

References

• Introduction to ISO8583 financial transaction message format
• Luhn algorithm
• Luhn Digit Calculator