802.15.4 Beacon Animation

Explore beacon interval, active superframe timing, CAP, CFP, GTS, and duty-cycle trade-offs

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802.15.4
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Interactive IEEE 802.15.4 beacon-enabled superframe workbench with BO/SO timing formulas, 16-slot visualization, CAP/CFP/GTS allocation, slotted CSMA-CA sequence, duty-cycle and battery estimates, and mobile-safe reference material.

802.15.4 Beacon Animation

Animation IEEE 802.15.4 Beacon mode

802.15.4 Beacon Superframe

Explore how a PAN coordinator uses beacons to synchronize sleepy devices, divide time into a 16-slot active superframe, reserve optional GTS slots, and trade latency against power saving.

983 msBeacon interval
25%Active duty cycle
12 CAPContention slots
30 dRough battery life
1Beacon sets time

The coordinator broadcasts a beacon every beacon interval so devices know when the next active period begins.

2BO controls interval

Beacon Order stretches the time between beacons. Larger BO usually means more sleep time.

3SO controls activity

Superframe Order sets the active duration. SO must not exceed BO in normal beacon-enabled operation.

4Slots split traffic

CAP is contention-based. CFP/GTS is scheduled. Inactive time is when devices can sleep.

1. Beacon

Coordinator announces timing.

2. Sync

Devices align to the slot clock.

3. CAP

Devices contend with slotted CSMA-CA.

4. CFP

Reserved GTS slots transmit.

5. Sleep

Inactive period saves energy.

6. Next

Cycle repeats at the next beacon.

Animated Beacon Cycle

The PAN coordinator sends a beacon that defines the superframe timing and wakes synchronized devices.

Stage Beacon
IEEE 802.15.4 beacon-enabled superframe animation A PAN coordinator, synchronized devices, 16-slot active superframe, CAP, CFP, inactive sleep period, and timing metrics update when Beacon Order, Superframe Order, GTS slots, and current assumptions change. Beacon-enabled PAN Beacon mode: synchronized superframes with CAP, optional CFP, and inactive sleep. PAN coordinator D1 sensor D2 meter D3 alarm D4 sleepy beacon Superframe timeline BI 983 ms, SD 245.8 ms, inactive 737.3 ms inactive sleep Slot 0 carries the beacon; CAP uses slotted CSMA-CA; CFP uses reserved GTS slots. CSMA-CA and GTS view 12 CAP slots 3 GTS slots 25% active CAP is above the 440-symbol teaching threshold.

Experiment Controls

Change BO and SO first. Then reserve GTS slots or test a traffic scenario to see how synchronization, power, latency, and CAP capacity move together.

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4
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45%
12 mA
5 uA
BeaconPredictable wake windows

Devices can wake near the next beacon, listen during needed slots, then sleep during the inactive period.

CAP OKCAP has contention space

Enough active slots remain for association, commands, and slotted CSMA-CA traffic.

Duty cycleLower duty cycle saves power

Battery life grows when BO is larger than SO, but latency and missed-beacon recovery can become harder.

Formula Trace

Calculating...

Reference Material

Beacon Superframe Quick Reference
Beacon interval

BI is the time between coordinator beacons. It is controlled by Beacon Order, BO.

Active duration

SD is the active superframe duration. It is controlled by Superframe Order, SO.

Allowed relationship

In normal beacon-enabled operation, 0 <= SO <= BO <= 14. SO larger than BO is invalid.

Sixteen slots

The active superframe is divided into 16 equal slots. Slot duration grows as SO increases.

Inactive period

If BO is greater than SO, the remaining beacon interval is inactive and devices may sleep.

SO equals BO

When SO equals BO, the active period fills the beacon interval and the duty cycle is 100%.

CAP, CFP, and GTS Notes
CAP

The Contention Access Period uses slotted CSMA-CA, so devices contend at aligned backoff boundaries.

CFP

The Contention-Free Period contains reserved Guaranteed Time Slots near the end of the active superframe.

GTS limit

802.15.4 allows up to seven GTS allocations in a superframe, subject to remaining CAP space.

Minimum CAP

The CAP must remain long enough for management traffic. This page highlights a 440-symbol teaching threshold.

CSMA-CA load

Higher traffic load increases contention in CAP. GTS can help time-critical devices avoid that contention.

Teaching model

This page treats each GTS allocation as one slot for clarity. Real allocations can vary by descriptor and implementation.

Power and Design Checklist
Low power

Increase BO relative to SO to create a longer inactive period, then verify that latency remains acceptable.

Low latency

Lower BO shortens the time to the next beacon, but devices wake more often and consume more energy.

Time-critical traffic

Use GTS when a device needs deterministic access inside the superframe and the coordinator can reserve slots.

Robustness

Long beacon intervals save energy but require good clock tolerance and careful missed-beacon recovery.

Non-beacon mode

Unslotted CSMA-CA can be simpler, but power saving and deterministic access move to higher layers.

Validate hardware

Battery estimates depend on radio current, sleep current, wake time, beacon tracking, retries, and application behavior.

Related Practice

802.15.4 CSMA-CA

Inspect the channel access algorithm used inside the CAP.

 802.15.4 GTS

Focus on guaranteed time slot allocation and deterministic access.

 802.15.4 Simulator

Connect beacon timing with frame building and channel access.

 Book chapter

Read the full PHY/MAC overview and related IoT protocol context.