How does periodic advertising differ from regular advertising?

Regular advertising is event-based with random jitter. Periodic advertising transmits at precise, fixed intervals (7.5 ms to 81.9 s) on data channels, allowing receivers to synchronize and wake only when a packet is expected. This saves receiver power and enables deterministic broadcast scheduling.

Periodic Advertising Sync Transfer allows a device already synchronized to a periodic train to share that synchronization info with another device over a connection, avoiding the slow scan-and-sync process. Essential for Auracast where a phone syncs to a broadcast and transfers the sync to earbuds.

Auracast is the Bluetooth SIG brand for LE Audio broadcast using periodic advertising. It enables one-to-many audio streaming in venues like airports, gyms, and conference rooms. Multiple receivers sync to the same periodic advertising train carrying LC3-encoded audio without individual connections.

Wireless Protocols

BLE Periodic Advertising

BLE Periodic Advertising (Bluetooth 5.0+) transmits extended payloads at precise, fixed intervals on data channels without requiring a connection. Receivers synchronize to the periodic train and wake only at the expected transmission time, saving power. It is the transport mechanism for Auracast (LE Audio broadcast), electronic shelf labels, and real-time indoor positioning systems. The interval ranges from 7.5 ms to 81.9 s.

Category: Wireless Protocols

Interval: 7.5 ms - 81.9 s

Understanding Periodic Advertising

Regular advertising includes random 0-10 ms jitter, making receiver timing unpredictable. Periodic advertising eliminates jitter: the advertiser commits to a fixed interval, and the scanner synchronizes to it. After synchronization, the receiver knows exactly when to wake, spending minimum time listening.

PAST (Periodic Advertising Sync Transfer) lets a connected device share its synchronization with a peer, enabling fast sync handoff. This is critical for Auracast, where a phone discovers and syncs to a venue broadcast, then transfers the sync parameters to connected earbuds.

Periodic Advertising Timing

Interval: 7.5 ms to 81.9 s (1.25 ms steps)
Payload: up to 255 bytes per event
Sync timeout: 100 ms to 163.84 s

Receiver duty cycle (100 ms interval):
Listen window ~2 ms / 100 ms = 2% duty cycle

Periodic vs Regular Advertising

Feature	Regular	Periodic
Timing	Interval + random jitter	Fixed interval, no jitter
Channels	37/38/39 primary	Data channels 0-36
Payload	31 B (legacy) / 255 B (ext)	255 B
Receiver sync	No (scan continuously)	Yes (wake on schedule)
Use case	Discovery, beacons	Auracast, ESL, positioning

Common Questions

Frequently Asked Questions

Periodic vs regular?

Regular has random jitter; periodic is deterministic. Receivers sync and wake only at expected times, saving power.

What is PAST?

Sync Transfer lets a synced device share sync info over a connection, enabling fast handoff (phone to earbuds for Auracast).

What is Auracast?

Bluetooth SIG brand for LE Audio broadcast. One-to-many audio streaming using periodic advertising with LC3 codec.

Related Terms

← Frequency Hopping BLE Power →

Broadcast Audio

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