BLE Advertising

BLE Advertising Overview

A BLE peripheral device can advertise to allow detection and connection by BLE central devices.

Advertising is governed by the Bluetooth GAP (Generic Access Profile) specification. Peripheral devices advertise to a Central device. Typically Peripheral devices have limited resources and use low power, while Central devices are more powerful and provide an interface for human interaction.

For GAP details, see below sections of Bluetooth Core Standard document,

Bluetooth Core Standard version 4, Vol 3, Part C, particularly sections 8 and 11
Core Specification Supplement, Part A

The Bluetooth GAP specification limits advertising data to two packets:

Advertising Data payload
Scan Response payload

For details of the format see BLE Advertising Data Format below.

BLE Advertising with BGX

The BGX supports:

advertising in high or low mode. See adv .
advertising service ID and name
turning off advertising. See adv .

By default, a BGX device advertises the BGX Streaming Service ID and the default module name. See UUID and Name for details.

Advertising Commands and Variables

Commands supporting BLE advertising are:

adv - advertise in high mode or low mode, or turn advertising off

Variables supporting BLE advertising are:

Advertising mode and settings:
- bl t c --- advertising and connection power
- bl v h d --- advertising high mode duration
- bl v h i --- advertising high mode interval
- bl v l d --- advertising low mode duration
- bl v l i --- advertising low mode interval
Advertising data:
- sy d n --- device name

BLE Advertising Data Format

The peripheral device transmits an advertising packet 31 octets in length. The central device scans and receives the advertising packet. The central can then request additional information. In response the peripheral sends a scan response packet, 31 octets in length.

The advertising packet and the scan response packet have the same general format.

The BLE advertising packet and scan response packet both consist of one or more structures of the form:

Length	Type	Content
1 octet	1 octet	Length - 1 octets

Length specifies the length of the data, not including the Length octet. The data consists of an octet specifying the data type, followed by the data content. Length = Content_length + Type_length = Content_length + 1

Unused octets are set to 00 .

The diagram below shows the general structure of the advertising packet and the scan response packet.

Source: Bluetooth Core standard v4, Vol 3, Part C - Generic Access Profile, Section 11, Advertising and Scan Response Data Format

BLE Advertising Format Examples

In the example tables, the top row shows the octets in the advertising packet or scan response packet, with data in hexadecimal notation. The Least Significant Byte (LSB) is on the left. Unless otherwise noted, data is sent in little-endian order. Some proprietary formats package the data in big-endian order.

The bottom line shows the interpretation, with numbers in decimal notation. Configurable parts of the advertising packet are emphasized .

UUID and Name

This is the default advertising mode for a BGX device, and the only advertising mode currently supported.


02	01	05	11	07	0011...EEFF	09	09	0011...6677
Length: 2	Type: Flags	Flags	Length: 17	Type: UUID	UUID: 16 octets	Length: 9	Type: Name	Name: 8 octets

UUID and name are determined as follows:

Value	Associated Variable	Default	Notes
`UUID`	None	`331a36f5-2459-45ea-9d95-6142f0c4b307`	BGX Streaming Service ID - see Xpress Streaming Service
name	sy d n	BGX-####	#### stands for the last 4 digits of the BD_ADDR - see bl a . Example: `BGX-F603`

Note : According to the BLE specification, the Service UUID appears in the advertising response as a hex number in little-endian order, with LSB first.

In the advertising packet, LSB at left: 07b3c4f04261-959d-ea45-5924f5361a33

The name is a string of ASCII character codes, and appears in the advertisement in the same order as the string. For example, the name BGX-F603 appears as 4247582D46363033 .

The entire advertisement, using the BGX Streaming Service ID and example name above, with LSB at left, appears as:

020106110707b3c4f04261959dea455924f5361a3309094247582D46363033

Note : When advertising with the 1M PHY, the maximum length of the name field in the BGX advertising packet is 8 characters. If the name of an advertising BGX ( sy d n ) exceeds 8 characters in length, it will be shortened in the advertising packet to its first 8 characters.

For example, the name:

BGX-12345

will appear in the advertising packet as:

BGX-1234

Version Notes: Starting with version 1.1.1229.0 , the BGX can advertise with both the 1M PHY and the LE Coded PHY (see bl p p and bl p m ). When advertising with the 1M PHY, the name field of the advertising packet is limited to 8 characters as described above. When advertising with the LE Coded PHY, the name field length is not limited in length and can be as long as the maximum allowable length for the System Device Name .