Understanding RX1 and RX2 with Network Latency

This page presents three simple examples to explain how LoRaWAN downlink reception works depending on network latency and responsiveness.

The device always opens two reception windows after each uplink:

• RX1 – opens shortly after sending
• RX2 – opens later, giving the network more time

If the network is slow or unstable, the response may arrive too late for RX1 and only RX2 will be usable.

Key Points:

• Low latency (100–300 ms)
• Server close to gateways
• Downlink ready quickly

Result:

• RX1 = OK ✔️
• RX2 is not needed

Key Points:

• Cloud-hosted server (AWS / Azure)
• Gateway in 4G
• Latency fluctuates (800 ms to 1.5 s)

Result:

• RX1 = Borderline ⚠️
• Sometimes RX1 works, sometimes the response arrives too late
• RX2 used as fallback ✔️

Recommendation: Increase RX1Delay (ex: 1 → 3 seconds)

Key Points:

• Weak cellular or satellite links
• High backend processing load
• Latency above 2–3 seconds

Result:

• RX1 = FAIL ❌
• RX2 = Only reliable option ✔️

• RX1 requires the network to respond quickly.
• RX2 provides a safety margin when the network is slow.
• Increasing RX1Delay helps but cannot fix very slow networks.