Problems to increase MQTT payload size for more than 2kb

[Felipe Dantas]

Hi everyone,

In nRF9160 with ncs 2.9.0 I've problems when trying publish a MQTT payload bigger than 2700 bytes aproximately. In advanced I already was adequated buffer size and put

"CONFIG_MQTT_MESSAGE_BUFFER_SIZE=4096 CONFIG_MQTT_PAYLOAD_BUFFER_SIZE=4096" lines in my prj.conf. I can't see faults in application log, but no data is received on broker. Looking for possibles llimitations in hardware, I figure out that 91 series modem have a limit on socket size of 2kb. Can I work around of this limitation by any other approach?

Send payloads up to 4096 bytes is an project requirement, and split payload in smaller parts is not an option at now.

Thanks for some help!

[Hakon]

Hello,

if you are using TLS then it won't work. The modem TLS data buffer is limited to 2KB, so any payloads bigger than that are not guaranteed to work. You can look at the MbedTLS stack instead if you want to increase the payload size.