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nRF9160 PSM active time strange behaviour

Hello everyone!

I have just got started working with Nordic devices, in particular the nRF9160. I have been doing tests using the provided UDP sample from nRF Connect SDK and a nRF9160DK board. I am connecting to Sweden's Telia network over LTE-M. I am using PSM and setting the active time (iDRX) to 20 seconds. However from the current consumption and terminal output of the device it seems that the modem is reentering cDRX mode and restarting the iDRX timer afterwards, although there is no data being sent to the nRF9160. The amount of reconnections also change from one transmission event to the next. I am still new to cellular networks and do not understand what can be going on here.

Best regards,

Tomás H.

PSM with active time

Transmitting UDP/IP payload of 78 bytes to the IP address 213.185.10.144, port number 4000
RRC mode: Connected
RRC mode: Idle

RRC mode: Connected
RRC mode: Idle

RRC mode: Connected
RRC mode: Idle

RRC mode: Connected
RRC mode: Idle

RRC mode: Connected
RRC mode: Idle

Transmitting UDP/IP payload of 78 bytes to the IP address 213.185.10.144, port number 4000

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0 user91187 over 4 years ago

Might look like PSM is not happening, can you turn on logging?

Regards,
Jonathan
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0 user113477 over 4 years ago in reply to user91187

Hi Jonathan!

I turned logging on and looked at the trace output with Wireshark. I can see that after sending data the modem receives a random amount of unintended TCP packets from several different sources. If this reception happens to be under the Active mode it triggers the modem back into RRC_CONNECTED state, as expected. I have no idea why these inbound TCP packets are being generated, but they would really impact the power consumption of my application. I attach the RAW and PCAP modem traces.

Best regards,

Tomás
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0 user113477 over 4 years ago in reply to user91187

Hi Jonathan!

I turned logging on and looked at the trace output with Wireshark. I can see that after sending data the modem receives a random amount of unintended TCP packets from several different sources. If this reception happens to be under the Active mode it triggers the modem back into RRC_CONNECTED state, as expected. I have no idea why these inbound TCP packets are being generated, but they would really impact the power consumption of my application. I attach the RAW and PCAP modem traces.

Best regards,

Tomás
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0 user91187 over 4 years ago in reply to user113477

I dont think there should be any TCP traffic so this is strange, what modifications have you done to the UDP sample?

Regards,
Jonathan
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0 user113477 over 4 years ago in reply to user91187

Right now I am using an almost unmodified version of the UDP sample application. I have changed the proj.conf to modify transmission interval and server address, and to set up the desired PSM configuration and modem tracing. The only change in main.c has been adding some text to the data being send over UDP. I attach both files to the message. The server I communicate with is currently unavailable, but I tried using the default "8.8.8.8" Google server and obtained similar results.

Best regards,

Tomás
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