eDRX: packets sent from server during idle period

RE: eDRX: packets sent from server during idle period

dejans — Mon, 16 Jun 2025 14:36:12 GMT

Hi Mark,

54 minutes is periodic TAU (T3412 timer expires) and it is expected that UE triggers the connection. UE monitors paging occasions according to paging time window. Signal levels are fine. This could indicate that there is a problem on the network side. It might be that the network does not support data transmissions in 81 seconds eDRX.

Best regards,
Dejan

RE: eDRX: packets sent from server during idle period

Achim Kraus — Mon, 16 Jun 2025 09:10:36 GMT

The capture shows a TAU request. Seems that's used even without PSM. Makes sense for me, to stay registered at the mobile network.

The pain will be now, to distinguish the TAU connect from one caused by eDRX "incoming data".

(I just have not that much experience running devices without PSM.)

RE: eDRX: packets sent from server during idle period

Mark Szente — Sun, 15 Jun 2025 14:18:19 GMT

Captured a longer trace that contains the event.

dejans the modem firmware version is 2.0.2

devzone.nordicsemi.com/.../trace_2D00_2025_2D00_06_2D00_14T15_2D00_37_2D00_46.053Z.mtrace

RE: eDRX: packets sent from server during idle period

Achim Kraus — Fri, 13 Jun 2025 14:16:29 GMT

OK, the idea "PSM TAU interval" doesn't fit, you already wrote, that you don't use PSM and the trace verifies that.

So, I don't know, why that modem gets a RRC active every 54 minutes.

I guess, it would require to capture that, but for that the modem trace must run for an hour.

RE: eDRX: packets sent from server during idle period

dejans — Fri, 13 Jun 2025 13:43:52 GMT

Hi,

Thank you for providing your modem trace.

Which modem firmware version do you use?

Best regards,
Dejan

RE: eDRX: packets sent from server during idle period

Mark Szente — Fri, 13 Jun 2025 12:44:31 GMT

Thanks for the heads-up! Here's the modem trace, hopefully it includes everything.

devzone.nordicsemi.com/.../trace_2D00_2025_2D00_06_2D00_13T12_2D00_37_2D00_54.224Z.mtrace

RE: eDRX: packets sent from server during idle period

Achim Kraus — Fri, 13 Jun 2025 12:24:33 GMT

That may be caused by the PSM TAU interval.

Let me add: if you provide a modem trace, than all infos are included and you will speed up the Nordic experts a lot. For the info you provide it frequently requires some questions back. If you feel not comfortable with such a trace in a public ticket, Nordic is able to make the ticket private.

RE: eDRX: packets sent from server during idle period

Mark Szente — Fri, 13 Jun 2025 12:08:17 GMT

Hello, thanks for the reply. I was using 2.56s for PTW. Changed it to 5.12 as suggested, but seeing the same results unfortunately - can't wake up the device. Went up to 10.24s but there is no change.

Also, it seems the device goes into RCC connected mode briefly every 54 minutes or so even without any packets sent from the server. Not sure if it's expected/related.

[00:00:15.146,270] <inf> xyz: RRC mode: Idle


[00:54:15.480,377] <inf> xyz: RRC mode: Connected

[00:54:15.671,600] <inf> xyz: RRC mode: Idle


[01:48:16.010,925] <inf> xyz: RRC mode: Connected

[01:48:16.200,164] <inf> xyz: RRC mode: Idle


[02:42:16.839,843] <inf> xyz: RRC mode: Connected

[02:42:17.050,048] <inf> xyz: RRC mode: Idle

RE: eDRX: packets sent from server during idle period

dejans — Thu, 12 Jun 2025 14:03:52 GMT

Hi,

Can you check what PTW is assigned to the device by the network using +CEDRXRDP command after eDRX and PTW have been negotiated? This could give information if the configuration was applied as expected.

Please note that our AT reference guide (see +CEDRXS set command) gives this instruction:
To ensure a proper amount of paging occasions and time for reception with all possible DRX cycle lengths, it is recommended to set the PTW length to ≥5.12 s for LTE-M and to ≥10.24 s for NB-IoT when possible.
Can you try using 81.92 s for eDRX cycle and 5.12 s for PTW?

Best regards,
Dejan

RE: eDRX: packets sent from server during idle period

Mark Szente — Thu, 12 Jun 2025 12:42:06 GMT

Only eDRX, not using PSM.

RE: eDRX: packets sent from server during idle period

Achim Kraus — Thu, 12 Jun 2025 12:05:44 GMT

Just to ensure:

Only eDRX is used, no PSM? Or is PSM enabled as well?

RE: eDRX: packets sent from server during idle period

Mark Szente — Thu, 12 Jun 2025 10:24:18 GMT

Interesting, thanks! Yes, in Hungary, only 21670 offers eDRX, so I'm going with them.

I could accept messages not being delivered and only RCC connected event is firing. However what annoys me is that I can't even wake up the device with 81.92 whatsoever. So I guess I have three options here:

- Go with 61.44 (just tested, also works with the above caveats)
- Have the device send some ping message every n minutes and act on the response if needed
- Use SMS

Obviously, all have their tradeoffs in terms of battery lifetime and/or operational cost. Also this sort of stuff requires actual field testing in each country...

RE: eDRX: packets sent from server during idle period

Achim Kraus — Wed, 11 Jun 2025 14:48:38 GMT

My experience with that here in Germany:

I use also 81.92s.

Two providers here deliver the messages, regardless when that have been sent.

One provider requires the message to be sent at most 10s ahead of the end of the idle period. If the message is sent out of that time window I just get a RRC connected event.

In Hungary (21630/LTE-M) I didn't get eDRX with a 1nce SIM. I only tested that with 81.92.