BLE Advertising packet format | BLE Data packet format

This page describes BLE (Bluetooth Low Energy) packet formats viz. BLE advertising packet format and BLE data packet format as per BLE specifications v4.2 and v5.1.

Introduction:
Bluetooth is the standard defined by Bluetooth SIG (Special Interest Group). The technology provides way to exchange information between wireless devices e.g. mobile phones, tablets, laptops, PDAs, printers and digital cameras. Bluetooth provides secure connection using 2.4 GHz ISM frequency band.

BLE Packet Format as per BLE v4.2

BLE Packet Formats v4.2-advertising packet,data packet

• Bluetooth Low Energy (BLE) protocol architecture has link layer which defines packet formats for advertising channel and data channel.
• The BLE packet format shown in the figure-1 is specified in as per Bluetooth Low Energy specification document v4.2, Vol.6, Part B, Sec.2.1.

Preamble: It is used by receiver for synchronization (time, frequency) and to perform AGC (Automatic Gain Control). It is predefined pattern of size 1 byte which is known to the receiver. Advertising packet use "10101010" in binary. Data packet use either "10101010" (if LSB of access address is 0) or "01010101" (if LSB of access address is 1) in binary form.

Access Address: For all advertising packet is uses fixed pattern "0x8E89BED6" in hexadecimal form with size of 4 octets. or 32 bits. For data packets it consists of 32 bit random value generated by BLE device in "initiating state". The same value is used in a "connection request (CONNECT_REQ)" message.

PDU:It consists of either "advertising channel PDU" or "data channel PDU" as defined in the figure.

CRC:It is 24 bit in size. It is calculated over PDU. It is used for error detection of the packet. CRC is calculated using polynomial of the form x²⁴ + x¹⁰ + x⁹ + x⁶ + x⁴ + x³ + x + 1.

BLE Advertising Packet

The advertising channel PDUs serve following functions.
• It broadcasts the data.
• It helps in discovering slaves in order to connect with them.
• There are different types of advertising PDUs each with different payload formats and functions.
➤Advertising PDUs ( ADV_IND, ADV_DIRECT_IND, ADV_NONCONN_IND, ADV_SCAN_IND)
➤Scanning PDUs (SCAN_REQ, SCAN_RSP)
➤Initiating PDUs (CONNECT_REQ)

BLE Data Packet

• It helps in transmission and reception of data between BLE devices after connection is established between them.
• The data channel PDUs are exchanged during scheduled "connection events".
• The maximum data payload is 246 bytes after deducting header, MIC and other useful informations carried by data channel PDU.