Release assistance indication %RAI with MQTT protocol

Question

Hello, 
 In the document about Release assistance indication %RAI. It says 
 
 In addition to using the %RAI command, the application must tell when the data connection is not needed anymore through the application domain data socket interface. 
 With the interface, the information can be given with the last data packet that is sent or after the application has received the data packet that ends the need for the connection. Each socket client tells their own need for the connection, and the information is combined in the modem domain.

1. Is using RAI feasible in MQTT protocol(because nrfcloud api use MQTT protocol)? 
 2. How can I tell the modem that last data packet is sent?

I would appreciate if someone could give me some advice about this. 
 
 Environment: 
 -Thingy:91 
 -NB-IOT 
 -NCS v1.6.0

Albrecht Markus Schellenberger · Accepted Answer

Hello Leo, 
 1. Is using RAI feasible in MQTT protocol(because nrfcloud api use MQTT protocol)? 
 
 Yes, RAI is possible to use with MQTT. But since MQTT is based on TCP (which means at least two packages, one UL TCP data followed by DL TCP ACK), RAI should indicate early release after receiving one package, though. 
 2. How can I tell the modem that last data packet is sent? 
 The modem will take care of this automatically. The only thing the application has to do here, is to switch to the right socket option. The Serial LTE modem application demonstrates how this can be done. 
 This pull request shows the available socket options . 
 I hope this answers your questions! 
 Regards, 
 Markus