How to Simulate Jitter Using fault

This guide explains how to introduce variable latency (jitter) into your application flow. Jitter is random, short‐term fluctuations in latency that can disrupt real‐time communication or stream quality.

Prerequisites

Install fault

If you haven’t installed fault yet, follow the installation instructions.
Basic Proxy Setup Be familiar with running fault run --with-[fault] commands from your terminal.

Light Ingress Jitter

In this example, incoming (ingress) traffic experiences a mild, random delay.

Inbound data from the server to the client is randomly delayed by up to 30ms, repeated at a frequency of 5 times per second, causing mild but noticeable fluctuations.

Start the proxy with jitter on ingress
```
fault run \
    --with-jitter \ # (1)!
    --jitter-amplitude 30 \ # (2)!
    --jitter-frequency 5 \ # (3)!
    --jitter-direction ingress # (4)!
```
1. Enable the jitter fault support
2. Set the amplitude which the maximum random delay added to each packet
3. Set the frequency representing how often jitter is applied per second
4. Apply the fault on ingress

Strong Egress Jitter

Here, you impose a larger jitter on outbound traffic, simulating choppy sends from the client to the server.

Outgoing data from the client can sporadically stall by up to 50ms, repeated 10 times a second. This is a heavier jitter that can disrupt interactive or streaming client uploads.

Start the proxy with jitter on egress
```
fault run \
    --with-jitter \ # (1)!
    --jitter-amplitude 50 \ # (2)!
    --jitter-frequency 10 \ # (3)!
    --jitter-direction egress # (4)!
```
1. Enable the jitter fault support
2. Set the amplitude which the maximum random delay added to each packet
3. Set the frequency representing how often jitter is applied per second
4. Apply the fault on egress

Bidirectional Jitter

Here, all traffic, whether inbound or outbound, suffers random short spikes. This is great for testing two‐way real‐time apps.

Start the proxy with jitter on egress and ingress
```
fault run \
    --with-jitter \ # (1)!
    --jitter-amplitude 30 \ # (2)!
    --jitter-frequency 8 \ # (3)!
    --jitter-direction both # (4)!
```
1. Enable the jitter fault support
2. Set the amplitude which the maximum random delay added to each packet
3. Set the frequency representing how often jitter is applied per second
4. Apply the fault on egress and ingress

Next Steps

Combine with Latency: For a more realistic environment, layer static latency (--with-latency) plus jitter for base latency + random spikes.
Vary the Frequency: If your application is bursty, reduce frequency for occasional stutters.
Apply Schedules: Use --jitter-sched to enable jitter in short intervals (e.g., [start:20%,duration:30%]), toggling unpredictably.

By adjusting amplitude and frequency and applying them to ingress, egress, or both, you can simulate a wide spectrum of jitter conditions—from slight fluctuations to severe choppy networks.