Every Bluetooth device has a unique 48-bit address called the BD_ADDR. The upper 24 bits of the BD_ADDR refer to the manufacturer specific address and are purchased through the IEEE Registration Authority. This address includes the Organization Unique Identifier (OUI), also known as the company ID, and is assigned by the IEEE. The 24 least significant bits are free for the company to modify.

Three other secure and randomized address formats are available but will be discussed in the BLE security portion of this chapter. The following diagram shows the BLE advertising packet structure and various PDU types. This represents some of the most commonly used  PDUs.