# What is channel utilization and why does it matter?

## What Channel Utilization Means

Channel utilization is the percentage of time the LoRa radio channel is occupied by transmissions. It's displayed in the [Meshtastic app](https://wiki.meshamerica.com/books/hardware-guide/page/meshtastic-app) as a percentage (visible in the channel info or device telemetry).

Think of it like a single-lane road. If utilization is 10%, there's plenty of room for everyone. At 25%, it's getting busy. Around 40-50%, there's constant congestion and collisions. At 80%+, the channel is saturated and very few packets get through.

## Why the 25% Threshold Matters

Meshtastic's flood routing uses random backoff timing to reduce collisions - nodes wait a random short period before retransmitting a packet. At low utilization, these collisions are rare. The ~25% figure is a community rule of thumb (not a hard physical constant): around 25% utilization, rising collision probability starts to degrade throughput noticeably, and once you reach roughly 40-50% the network becomes largely unusable.

## What Drives High Channel Utilization

In order of typical impact:

1. **Position broadcast interval too short** - The default fixed position broadcast interval is 15 minutes, but users can lower it, and with smart broadcast enabled a moving node can transmit as often as every 30 seconds (the smart-broadcast minimum). On a 100-node network with everyone broadcasting every 30 seconds, position traffic alone saturates the channel. Fix: set position broadcast to 5-30 minutes for fixed nodes, 1-5 minutes for mobile nodes. `meshtastic --set position.position_broadcast_secs 1800`
2. **Telemetry too frequent** - If many nodes broadcast device/environment telemetry at 5-minute intervals, the aggregate airtime adds up. Fix: set telemetry intervals to 15-30 minutes.
3. **Long-range preset with many nodes** - The Long Slow preset uses a high spreading factor, so each packet takes on the order of several seconds of airtime (the exact figure depends on payload size and bandwidth). With 50+ nodes, even moderate message rates saturate the channel. Fix: migrate to Medium Slow or Medium Fast, which cut airtime per packet substantially; note this trades some range for much lower airtime.
4. **High hop limits creating more retransmissions** - Total airtime for a packet scales with the number of nodes that actually rebroadcast it, so lowering the hop limit (for example from 5 to 3) reduces airtime by an amount that depends on how many relays would otherwise have re-transmitted, not a fixed percentage.
5. **Too many Router role nodes** - Every node set to ROUTER retransmits every packet it hears. In a dense area, CLIENT nodes should outnumber ROUTER nodes significantly. Fix: set personal handheld devices to CLIENT role, not ROUTER.

## Target Values for a Healthy Network

<table id="bkmrk-channel-utilizations"><thead><tr><th>Channel Utilization</th><th>Status</th><th>Action</th></tr></thead><tbody><tr><td>0-10%</td><td>Healthy</td><td>None needed</td></tr><tr><td>10-25%</td><td>Moderate</td><td>Monitor; consider reducing position intervals</td></tr><tr><td>25-40%</td><td>Congested</td><td>Reduce intervals; consider faster preset</td></tr><tr><td>40%+</td><td>Saturated</td><td>Immediate action needed: reduce broadcasts, change preset</td></tr></tbody></table>