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CARD NUMBER FORMATS
When a contactless or prox card is presented to a reader, the reader captures the number that is programmed into that card over a radio frequency (RF) interface. The reader then sends that number to the system that grants access to doors, networks, or applications on a PC. The various shapes that the card number might have are called formats.
FACILITY CODE AND CARD NUMBERS
Cards are programmed with 0s and 1s, which are often arranged into sections – the facility code or prefix which is the same for each card; and the ID number which is different for each card. The access control system looks first to see that the facility code is correct for that facility, and then it checks the ID number of the card for the requested permission. Sometimes a format is designed without a facility code, in which case each card has a longer ID number.
The most common card format is the 26-bit open format, with available facility codes between 0 and 255, and ID numbers between 0 and 65,535. Other common formats are 34-bits, 35-bits (often called Corporate 1000) and 37-bits.
UNIQUE CARD NUMBERS
It is very important that every card enrolled in a system be recognized by that system as unique. If a particular format cannot meet the requirements of a large institution, it will be difficult to avoid the collision of ID numbers in the system. In the case of the 26-bit format, for each facility code there are only 65,535 unique ID numbers. Upon exhausting all the ID numbers for one facility code, it is possible to create another facility code and start over at 0 with new ID numbers. However, some systems are configured to only look at the ID numbers , resulting in ID number collisions. Here is an example of two cards that could cause this problem:
CARDS AND MORE THAN ONE SYSTEM
Many institutions have a local access control system which manages all the prox card numbers locally. However, some institutions use a Single Sign-On application such as Imprivata, which is managed centrally for several institutions. In this configuration, a prox card number which is unique to the local access control system could collide with other prox card numbers in the enterprise SSO application, especially if the latter were only looking at the ID numbers and not the facility codes.
As organizations grow, their card formats must grow with them, in order to provide enough unique ID numbers. Formats such as Corporate 1000, which has over 1,000,000 ID numbers per facility code, and a 32-bit format with 1000 facility codes and over 2 million ID numbers are available for programming into all types of contactless cards. ColorID has helped thousands of institutions select formats and configure their various systems and readers to read those formats.