What is the iBeacon Bluetooth Profile

For an iBeacon with ProximityUUID E2C56DB5-DFFB-48D2-B060-D0F5A71096E0, major 0, minor 0, and calibrated Tx Power of -59 RSSI, the transmitted BLE advertisement packet looks like this:

d6 be 89 8e 40 24 05 a2 17 6e 3d 71 02 01 1a 1a ff 4c 00 02 15 e2 c5 6d b5 df fb 48 d2 b0 60 d0 f5 a7 10 96 e0 00 00 00 00 c5 52 ab 8d 38 a5

This packet can be broken down as follows:

d6 be 89 8e # Access address for advertising data (this is always the same fixed value)40 # Advertising Channel PDU Header byte 0.  Contains: (type = 0), (tx add = 1), (rx add = 0)24 # Advertising Channel PDU Header byte 1.  Contains:  (length = total bytes of the advertising payload + 6 bytes for the BLE mac address.)05 a2 17 6e 3d 71 # Bluetooth Mac address (note this is a spoofed address)02 01 1a 1a ff 4c 00 02 15 e2 c5 6d b5 df fb 48 d2 b0 60 d0 f5 a7 10 96 e0 00 00 00 00 c5 # Bluetooth advertisement52 ab 8d 38 a5 # checksum

The key part of that packet is the Bluetooth Advertisement, which can be broken down like this:

02 # Number of bytes that follow in first AD structure01 # Flags AD type1A # Flags value 0x1A = 000011010     bit 0 (OFF) LE Limited Discoverable Mode   bit 1 (ON) LE General Discoverable Mode   bit 2 (OFF) BR/EDR Not Supported   bit 3 (ON) Simultaneous LE and BR/EDR to Same Device Capable (controller)   bit 4 (ON) Simultaneous LE and BR/EDR to Same Device Capable (Host)1A # Number of bytes that follow in second (and last) AD structureFF # Manufacturer specific data AD type4C 00 # Company identifier code (0x004C == Apple)02 # Byte 0 of iBeacon advertisement indicator15 # Byte 1 of iBeacon advertisement indicatore2 c5 6d b5 df fb 48 d2 b0 60 d0 f5 a7 10 96 e0 # iBeacon proximity uuid00 00 # major 00 00 # minor c5 # The 2's complement of the calibrated Tx Power

Any Bluetooth LE device that can be configured to send a specific advertisement can generate the above packet. I have configured a Linux computer using Bluez to send this advertisement, and iOS7 devices running Apple's AirLocate test code pick it up as an iBeacon with the fields specified above. See: Use BlueZ Stack As A Peripheral (Advertiser)

This blog has full details about the reverse engineering process.

It seems to based on advertisement data, particularly the manufacturer data:

4C00 02 15 585CDE931B0142CC9A1325009BEDC65E 0000 0000 C5<company identifier (2 bytes)> <type (1 byte)> <data length (1 byte)>    <uuid (16 bytes)> <major (2 bytes)> <minor (2 bytes)> <RSSI @ 1m>

• Apple Company Identifier (Little Endian), 0x004c
• data type, 0x02 => iBeacon
• data length, 0x15 = 21
• uuid: 585CDE931B0142CC9A1325009BEDC65E
• major: 0000
• minor: 0000
• meaured power at 1 meter: 0xc5 = -59

I have this node.js script working on Linux with the sample AirLocate app example.

Just to reconcile the difference between sandeepmistry's answer and davidgyoung's answer:

02 01 1a 1a ff 4C 00

Is part of the advertising data format specification [1]

  02 # length of following AD structure  01 # <<Flags>> AD Structure [2]  1a # read as b00011010.      # In this case, LE General Discoverable,     # and simultaneous BR/EDR but this may vary by device!  1a # length of following AD structure  FF # Manufacturer specific data [3]4C00 # Apple Inc [4]0215 # ?? some 2-byte header

Missing from the AD is a Service [5] definition. I think the iBeacon protocol itself has no relationship to the GATT and standard service discovery. If you download RedBearLab's iBeacon program, you'll see that they happen to use the GATT for configuring the advertisement parameters, but this seems to be specific to their implementation, and not part of the spec. The AirLocate program doesn't seem to use the GATT for configuration, for instance, according to LightBlue and or other similar programs I tried.

References:

1. Core Bluetooth Spec v4, Vol 3, Part C, 11
2. Vol 3, Part C, 18.1
3. Vol 3, Part C, 18.11
4. https://www.bluetooth.org/en-us/specification/assigned-numbers/company-identifiers
5. Vol 3, Part C, 18.2