max value MQTT_MESSAGE_BUFFER_SIZE

[ActiTAG]

Hello,

I come to you because I did not find the information on the web about sending MQTT data. I send a buffer of size 1408 with MQTT but I see in the configuration that MQTT_MESSAGE_BUFFER_SIZE = 1024. I wanted to know if this is the maximum that I can send per message(Max value is 1024?) and will my message be sent in multiple times if my message exceeds the value?

Thanks in advance for your answer :) 

[Albrecht Markus Schellenberger]

Hello Tatiana,

the maximum message buffer size is limited by the TLS message size of the modem, which is:

/**@brief Maximum TLS message size in bytes. */
#define NRF_MODEM_TLS_MAX_MESSAGE_SIZE 2048

See ../nrfxlib/nrf_modem/include/nrf_modem_limits.h.

It is also mentioned in the modem firmware relase notes:

*** Limitations

***************

- TLS/DTLS

- ...

- 2kB secure socket buffer size.

Otherwise, you should be good to go! :-)

Regards,

Markus

[Albrecht Markus Schellenberger]

And I forgot to mention: one MQTT message can be divided into several TCP packages.

Regards,

Markus

[ActiTAG]

Thank you for your answer! So one  MQTT message size is defined by MQTT_MESSAGE_BUFFER_SIZE and the max per message is  NRF_MODEM_TLS_MAX_MESSAGE_SIZE 2048, isn't it?

[Albrecht Markus Schellenberger]

Yes, that is correct! :-)

Regards,

Markus