BLE Extended Advertising
Understanding Extended Advertising
Legacy advertising transmits the entire payload on all 3 primary channels, limiting size to 31 bytes and creating congestion. Extended advertising separates the mechanism: a minimal ADV_EXT_IND on primary channels contains only a pointer (channel, offset, PHY) to secondary advertisements on data channels 0-36 where larger payloads are sent once.
Advertising sets allow a device to maintain multiple independent advertising configurations simultaneously, each with its own address, data, timing, and PHY. Periodic advertising establishes a predictable schedule on data channels for connectionless broadcast, used by Auracast (LE Audio broadcast) and electronic shelf labels.
Extended: 255 B payload on data channels
Primary ADV_EXT_IND: ~15 bytes (pointer only)
Secondary AUX_ADV_IND: up to 255 bytes
Advertising Feature Comparison
| Feature | Legacy (4.x) | Extended (5.0+) |
|---|---|---|
| Max payload | 31 bytes | 255 bytes |
| Channels | 37/38/39 only | 37/38/39 + data ch |
| Advertising sets | 1 | Multiple |
| Periodic mode | No | Yes |
| Coded PHY | No | Yes (long range) |
Frequently Asked Questions
How does it work?
Short ADV_EXT_IND on ch 37/38/39 points to AUX_ADV_IND on a data channel with the full payload. Reduces primary channel congestion.
Periodic advertising?
Fixed-interval broadcast on data channels without connection. Used for Auracast audio, indoor positioning, and electronic shelf labels.
Backward compatible?
BLE 4.x scanners can't see extended ads. Advertisers can transmit both legacy + extended simultaneously via advertising sets.