ACK/NACK Timing Visualizer

Visualize acknowledgments, negative acknowledgments, timeout margins, and retransmission timing

ACK/NACK Timing Visualizer

Animation Reliability Timing

ACK/NACK Timing Visualizer

Reliable protocols are timing decisions. This workbench shows a sender waiting for feedback, a receiver returning ACK or NACK, and the timeout boundary that decides whether the sender waits, retries, or creates duplicate traffic.

ACK before timeout current timing result

420 ms observed feedback time

380 ms timeout margin

0 retries extra transmissions

What

A data packet starts a timer. Feedback from the receiver either confirms delivery, reports an error, or arrives too late.

Why

Timeouts that are too short waste energy and airtime. Timeouts that are too long make real loss recovery slow.

Try First

Press Step Event. Watch DATA cross to the receiver, ACK return, and the timeout line decide whether retry happens.

Notice

ACK confirms success. NACK reports known failure. Silence is ambiguous, so the sender waits until timeout.

Controls

Timing Model

Scenario CoAP balanced CoAP balanced Timeout too short NACK repair Duty-cycled radio

Round-trip time 300 ms

Jitter sample 60 ms

ACK delay 60 ms

Timeout 800 ms

Receiver feedback ACK ACK received Late ACK ACK lost NACK returned

Scenario Presets

Timing and Retransmission Workbench

A confirmable IoT message receives feedback before timeout, so the sender cancels the timer and avoids retransmission.

ACK before timeout

Learning Support

ACK means stop waiting

Once an ACK arrives, the sender cancels the retransmission timer for that packet or message.

NACK is faster than silence

A NACK tells the sender that the receiver detected a problem. The sender can retry without waiting for timeout.

Timeout handles uncertainty

If no feedback returns, the sender cannot tell whether data, ACK, or radio access failed. Timeout is the fallback.

Late ACKs create duplicates

If timeout fires before a valid ACK returns, the sender may retransmit data the receiver already accepted.

Quick Reference

Observed feedback

feedback = RTT + ACK_delay + jitter

This page uses a simple teachable model for one message exchange.

Timeout margin

margin = timeout - feedback

Positive margin means feedback arrives before timeout. Negative margin means timeout fires first.

Safe starting point

safe_timeout = RTT + ACK_delay + 2*jitter

This is a planning rule of thumb, not a TCP replacement.

TCP RTO idea

RTO uses smoothed RTT and variance

TCP adapts over time. Many IoT protocols use simpler timers or application-level policies.

ACK

positive acknowledgment

The receiver confirms that the packet or message was accepted.

NACK

negative acknowledgment

The receiver explicitly reports a missing or corrupted item when the protocol supports it.

Retry cost

extra_tx = retransmissions

Every retry spends airtime, energy, and channel capacity.

Duplicate risk

timeout < feedback

A late ACK can arrive after a retry was already sent, so duplicate detection matters.

Guided Practice

Make timeout too short

Use Short timeout. The timer fires before ACK, producing a spurious retransmission.

Repair with NACK

Use NACK repair. Notice that explicit negative feedback starts recovery before timeout.

Add duty-cycle delay

Use Duty-cycle delay. The ACK is valid, but the receiver waits before it can transmit it.

Find the margin

Increase jitter until timeout margin becomes small. This is where rare radio delays can cause retries.

Network Conditions EmulatorExplore delay, loss, jitter, and their effect on protocols. MQTT QoS SimulatorSee acknowledgment patterns in QoS 1 and QoS 2 delivery. Protocol State PlaygroundConnect timing events to sender and receiver states. Packet FragmentationCompare reliability timing with packet loss and reassembly.