ISO 8583 Tutorial – Introduction for Beginners

http://jimmod.com/blog/2011/07/25/jimmys-blog-iso-8583-introduction-beginners-tutorial/

ISO 8583 Tutorial article

• Introduction for Beginners
• Build and Parse ISO Message using JPOS library

Introduction

Lately I’ve handle several financial project that allow me to understand bank and financial transaction better.
All (or most?) financial transaction is using ISO 8583 standard, which at first I thought is a complicated standard. But after learn and see how it implemented it’s not as complex as I thought.
In this post I will try to explain (based on my experience  before I go deeper on the programming side.

Although it’s a ‘standard’ I see that’s many variant for the detail implementation of ISO 8583.

Financial transaction is communication between 2 system through socket connection.
After connection established, each system can send message in ISO 8583 format which commonly will be request and the other system will response.
From my experience the communication will be start with sign on and then the financial transactions.
Periodically an echo message is send to make sure the other system is still alive.

If I break down the flow:

1. System A open connection to System B (through specific IP and Port).
2. Connection established.
3. System A send Sign-On request message.
4. System B send Sign-on response message.
5. System A will start send Echo request message periodically (e.g every 1 minute).
6. System B will send Echo response message when receive Echo request message.
7. When financial transaction happen, System A will send Transaction request message.
8. Then System B will send Transaction response message.
9. If something wrong happen (usually timeout so System A didn’t get the response), System A will send Reversal request message to cancel the previous transaction.
10. System B will send Reversal response message.

I hope my explaination give clear basic understanding about the flow.
Next the question will be what’s this ISO 8583 message looks like.
We can separate the message into 3 parts:

• Message Type Identifier
• Bitmaps
• Data Elements

ISO8583 - structure

Message Type Identifier

Message Type Identifier or MTI is 4 digits numeric that describe the message type. It will explain the message function.
Commonly used:
- 02xx : Financial Message (e.g 0200 for request, 0210 for response)
- 04xx : Reversal Message (e.g 0400 for request, 0410 for response)
- 08xx : Network Management Message (e.g 0800 for request, 0810 for response)
* I found more detail & complete list at wikipedia

Bitmaps

Bitmaps is field that contain information about which data element is presence or absence. Based on the variant it could be 16 hexadecimal characters.
An example will make it clear.

The bitmap is:

B220000000100000

If we break down to binary (I hope you understand how to convert hexadecimal to binary:) :

1011001000100000000000000000000000000000000100000000000000000000

Since I’m nice  I create graphical illustration.

Bitmap sample

You can see that in this bitmap it explain that data element in the message is 1, 3, 4, 7, 11.
There’s special meaning of first bit of bitmap, if it has value of 1 that mean there’s secondary bitmap.
And what the hell is this secondary bitmap?
Since 16 hexadecimal characters will can only contain info of 64 data element, some transactions contain data element number 64 – 128. That mean the 16 hexadecimal characters is not sufficient.
With set the first bit to ’1′ that will inform there’s additional bitmap, which is another 16 hexadecimal characters.
So in this case the full bitmap example should be:
B2200000001000000000000000800000
Convert to binary:
10110010001000000000000000000000000000000001000000000000000000000000000000000000000000000000000000000000100000000000000000000000
From the bitmap, data element presence in the message : 3, 4, 7, 11, 105.

Sample Bitmap complete

Data Elements

Data Elements is the essense of the whole ISO message, contain information about the transaction (transaction type, amount, customer id, etc).
Each data element have their on format, attribute and length.
Each data element number also have standard purpose, for example DE #4 is transaction amount.
I will explain based on the example above, since this is only introduction I don’t want to confuse beginner reader. In wikipedia there’s full list.
For our examples, the data element list:

• #3 – Processing code – n 6
• #4 – Transaction amount – n 12
• #7 – Transmission date & time – n 10
• #11 – Systems trace audit number – n 6
• #44 – Additional response data – an ..25
• #105 – Reserved for ISO use – ans …999

To make it practical let’s just use example.
We want to send :

• DE #3 : 201234
• DE #4 : 10000
• DE #7 : 1107221830
• DE #11 : 123456
• DE #44 : A5DFGR
• DE #105 : ABCDEFGHIJ 1234567890

Using above value, the data in data elements :

ISO8583 - de

Based on the type each value will be formatted.

• a : alpha (including blanks)
• n : numeric value
• s : special characters
• x (no dot) : length is x (fixed)
• .x (one dot) :  max length is x (1 digit in front as length info)
• ..xx (two dot) :  max length is xx (2 digit in front as length info)
• …xxx (three dot) :  max length is xxx (3 digit in front as length info)

ISO Message

From above examples the whole ISO message will be :

0200B2200000001000000000000000800000201234000000010000110722183012345606A5DFGR021ABCDEFGHIJ 1234567890

Conclusion

Ok. This article already long enough 
Actually I always prefer short article, but on this case it’s cannot be to short.
Anyway, I hope this article is clear enough for you.