RE: aws_iot MQTT subscriber keep alive

Charlie — Tue, 21 Dec 2021 12:25:46 GMT

Hi Ted,

[quote user=""]I'm writing to ask about how long a device running Nordic's aws_iot sample app (sdk-nrf 1.6.1 based, Zephyr 2.6.0 based) may be in a "radio idle" state, and the device still wake the radios and be able to receive messages to which its firmware has subscribed?[/quote]

The "radio idle" state length is the parameter "RRC inactivity timer", which is decided by the Cellular IoT network you used. According to Online Power Profiler for LTE, most operators use 7 seconds. You can check with a PPK like a demo from User guide (LTE), or ask your cellular network provider.

[quote user=""]When I increase the firmware's "radio idle" period, I begin to lose subscription reception at about five minutes idle period.[/quote]

Which configuration have you modified since this can not be controlled by UE? Did you actually modify CONFIG_LTE_PSM_REQ_RPTAU?

[quote user=""]In the app prj.conf file, I see no mention of PSM (power savings mode?) settings. [/quote]

You can change PSM settings through Kconfig Menu or add and modify following lines to prj.conf:

CONFIG_LTE_PSM_REQ_RPTAU="00000011"
CONFIG_LTE_PSM_REQ_RAT="00100001"

[quote user=""] Is this correct understanding?[/quote][quote user=""] Should I be looking for some kind of keep alive parameter other than `CONFIG_MQTT_KEEPALIVE`?[/quote]

This is correct understanding as long as the MQTT connection is ALIVE. nRF9160: AWS IoT sample document mentions that NAT timeout could also affect. I found another case that has very similar symptoms as your issue, and it was solved by changing to another network.

Best regards,

Charlie