What Is a Beacon Protocol?
A beacon protocol is the set of rules that tells a thumb-sized radio how often to speak, what to say, and how loudly to say it—then tells receivers how to interpret that single breath of data. Built atop Bluetooth Low Energy advertising packets, these grammars turn raw 2.4 GHz energy into structured messages that phones, gateways, or forklifts can trust.
The Advertising Frame: 31 Bytes of Poetry
At its heart lies a 31-byte payload divided into length-type-value triplets. A single triplet might announce a 128-bit UUID, a 16-bit major/minor pair, or a temperature reading. The first byte declares length, the second the data type, the remaining bytes the payload itself. Miss one byte and the whole stanza collapses; parsers simply skip to the next length byte, making the frame self-healing even in noisy air.
Timing Rules: The Metronome of the Air
Legacy advertising fires every 100 ms—fast enough for a lock to open before a user tugs the handle. Energy-misers stretch to 900 ms, trading latency for years of coin-cell life. Bluetooth 5.2 introduced decision-based advertising: the beacon listens for 80 µs, evaluates RSSI and channel-busy flags, then skips the slot if interference is high. The result is a polite neighbour that speaks only when the air is quiet.
Calibrated Power: Speaking at the Right Volume
The one-byte RSSI value embedded in the frame is not raw signal—it is a signed integer telling receivers what signal strength to expect at one metre. A phone compares this reference to the actual RSSI and infers distance without ever shaking hands. Miscalibrate by 3 dB and your “unlock at 1 m” becomes “unlock at 1.5 m”—enough to frustrate users and drain batteries faster.
Security Layers: Trust in a Whisper
Rolling identifiers rotate every 15 minutes, seeded by a 64-bit factory key. Over-the-air firmware updates are signed with ECDSA; rollback protection fuses old firmware hashes into silicon. The result is a device that can be trusted even though it never pairs, never encrypts, and never asks for a password.
Real-World Dialects: iBeacon, Eddystone, AltBeacon
iBeacon speaks Apple’s terse UUID-major-minor triad; Eddystone adds URL, telemetry, and encrypted frames; AltBeacon offers an open, royalty-free alternative. Each dialect respects the same 31-byte canvas but paints different pictures—coupons, web links, or sensor data—without breaking the grammar.
Collision & Coexistence: Grammar in a Crowd
When forty beacons share the same corridor, probability theory becomes grammar. Randomised advertising intervals (±10 ms) spread packets across time; decision-based skipping spreads them across frequency. The result is a polite conversation where every voice can still be heard.
The Road Ahead: Towards Zero-Byte Silence
Bluetooth 6.0 introduces periodic advertising with responses, allowing thousands of tags to share the same channel without collision. Future revisions may drop the payload to zero bytes, using only the presence or absence of a tone as the message. The protocol will have achieved its ultimate form: silence that still speaks volumes.
Conclusion: Grammar That Outlives the Speaker
A beacon protocol is not a product; it is a contract between transmitter and receiver, written in microseconds and milliwatts. Long after the plastic shell has yellowed and the battery has leaked, the grammar endures—ensuring that tomorrow’s radios can still understand today’s whispers.
