Nrf9160 DK does not send periodic TAU when no tx is due

Question

Hi, 
 in NB-IOT the UE should make a Traffic Area Update TAU when timer T3412 expires. I have a project based on the UDP_with _PSM sample. When I configure the PSM timer to be 1 minute and a data transmission every 10 minutes, it is my understanding that the UE should do the TAU every minute even if there is no data to transmit. However the UE only does a TAU after sending data every 10 minutes. 
 I have tried different settings for the defines below, but these are the current ones 
 #define CONFIG_LTE_PSM_REQ_RPTAU "10100001"
#define CONFIG_LTE_PSM_REQ_RAT "00100000" 
 DK version is 0.8.2, and I tried with ConnectSDK Tag v0.4.0 and v1.0.0. Modem firmware is 1.0.1 
 Any help would be appreciated. 
 -David

GNotman · Accepted Answer

The UE can request certain PSM timers however, the network must agree to the requested timers. 
 The network may agree the requested timers, override the request with their own values, or simply not allow PSM. 
 
 A 1 minute T3412 timer is very short, I would be surprised if the network would allow it. 
 
 Also I believe your T3324 (Requested RAT) value is invalid. You are you requesting 1m. x 0. 
 You can request both the T3324 and T3412 to be the same duration. 
 This works, however, the UE will remain active throughout the PSM cycle. 
 
 After the PSM request has been sent you can view the actually in use timers with either: 
 AT+CPSMS? 
 AT%XMONITOR 
 Note: You may need to wait a few seconds after the initial request is sent.

Nrf9160 DK does not send periodic TAU when no tx is due

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