NRF52840 Thread publish max payload length

[Leandro Zimmer]

Hi,

What's is the max length for the payload data in "mqttsn_packet_sender_publish" method?

EDIT:

Redefining my question above:

What's is the max length for the payload data in "mqttsn_packet_sender_publish" method, for sending only one packet of 127bytes, without fragmentation?

Thanks,

Zimmer

[haakonsh]

I believe the maximum message length is 2^16 bytes as the set and get length functions operate with uint16_t, given that there is enough space in the buffer and message queue ofc. 

[Leandro Zimmer]

My question is because of the specifications:

• IEEE 802.15.4 – 127 bytes (payload)

[haakonsh]

Max packet length of 802.15.4 MAC layer is 127 bytes and the 6LoWPAN layer will dis/assemble its packets to/from 127 byte MAC layer packets. This means that from the application perspective you can operate on packets much larger than 127 bytes. 

[Leandro Zimmer]

Thank you. I understand. Then I redefine my question.
What's is the max length for the payload data in "mqttsn_packet_sender_publish" method, for sending only one packet of 127bytes, without fragmentation?

[haakonsh]

Hmm that is dependent on the MQTTSN protocol overhead who in turn is dependent on the Thread stack overhead (UDP packet over 6LoWPAN), and both MQTTSN and 6LoWPAN probably have options and configurations that increase/decrease that overhead. We're a bit short staffed during the summer vacation, but i'll try to find an answer, it's buried in the Thread and MQTTSN spec somewhere.