LTE connection timeout after 30x modem on/off

RE: LTE connection timeout after 30x modem on/off

MBeonas — Wed, 20 Jan 2021 15:27:14 GMT

Looks like the modem is able to get a LTE connection again after a while.

Thank you for your helpful answer and your pointers.

Best Regards

Martin

RE: LTE connection timeout after 30x modem on/off

Heidi — Wed, 20 Jan 2021 12:58:11 GMT

It's the GSMA specified Radio Policy Manager (RPM) feature which is blocking the ATTACH command. RPM is used for protecting the network from excessive signaling loads in various scenarios. In this case, the default value 30 is used for PDP Context Activation Requests (TS.34 - IoT Device Connection Efficiency Guidelines page 43 TS.34_8.2.4_REQ_010).

This is implemented in the modem firmware. I don't believe there's any way for the user to change this default value, but I will double-check with the developers.

[quote user="MBeonas"]I was about to start preparing a Modem Trace. Is this still needed?[/quote]

If you have confirmed that the device is able to connect to the network again if you wait an hour, a modem trace is not needed as this isn't a bug.

If you're enabling/disabling the LTE modem to get a GPS fix, you could try setting a higher priority on the GPS process (https://github.com/nrfconnect/sdk-nrf/pull/2711).

And putting a lower accuracy threshold on the GPS fix will give you a lower TTFF as well (https://github.com/nrfconnect/sdk-nrf/pull/3427).

Best regards,

Heidi

RE: LTE connection timeout after 30x modem on/off

MBeonas — Wed, 20 Jan 2021 11:35:49 GMT

Hi Heidi,

I was about to start preparing a Modem Trace. Is this still needed?

Where is this threshold of 30 attaches per hour defined/documented? Is this defnied by the modem or by the LTE standard? Is there any way to change this limit?

We are planning on a low-latency tracking mode with our software in which we are recording GPS for one minute, then enable the LTE modem to upload the data and then switch back to GPS tracking as fast as possible.

We need to put the modem in offline state for that. If we would rely on the modem for re-enabling the GPS while we are still connected to a LTE network, the modem needs to wait in LTE mode for the RRC timeout until it can switch back to GPS. That timeout is >20s with our carrier which is hardly acceptable regarding lost GPS data points.

RE: LTE connection timeout after 30x modem on/off

Heidi — Tue, 19 Jan 2021 11:57:59 GMT

Hi again,

[quote user=""]On the 30th cycle (31st time switching the modem on after power-on reset), we suddenly fail to get a LTE connection and run into our timeout handling. All subsequent tries also fail.[/quote]

Could you check if it is able to connect again after one hour?

You're only allowed to do 30 attaches per hour, so if you exceed this limit you have to wait another hour before you can connect again.

RE: LTE connection timeout after 30x modem on/off

Heidi — Mon, 18 Jan 2021 18:04:41 GMT

Hi!

Thanks for the report. Are you able to take a modem trace when this issue occurs?

Best regards,

Heidi