What defines the maximum payload size and transmission time? (AU915)

ElectronicallyE
Tue, 06 May 2025 07:17:48 +0000
End Devices (Nodes)

A number of forum posts talk about the maximum permitted payload size, however, don’t discuss why there is a limit:

Maximum “Universal” Application Payload Size - End Devices (Nodes) - The Things Network

How to Find Maximum Packet Size - The Things Network

What is the maximum number of characters I can send with LMiC? - End Devices (Nodes) / LMIC - The Things Network

Reviewing the RP002-1.0.4 Regional Parameters, under 2.8.6 AU915-928 Maximum Payload Size, it states the following:

The maximum MACPayload size length (M) is given by the following table for both uplink dwell time configurations: No Limit and 400ms. It is derived from the maximum allowed transmission time at the PHY layer, taking into account a possible repeater encapsulation.

What is the “maximum allowed transmission time at the PHY layer” and how is it determined? Is this called out in documentation?
Given that in Australia there is no duty cycle limit, why is there a “maximum allowed transmission time”?

15 posts - 5 participants