eDRX: packets sent from server during idle period

[Mark Szente]

Hello,

I have been observing some interesting behavior concerning packets sent from server during eDRX idle period. When the period is set to 20.48s or 40.96s, any packet sent will make the device transition to RCC connected state as soon as the idle period ends. However, packets are only received if they were sent a few seconds before the PTW. I guess that's expected, though, as networks may not keep the packets for more than a few seconds.

However, when using 81.92s, which is my goal, I cannot make the device wake up at all. Even if I spam packets every second, or even 0.5 seconds, it won't ever switch to RRC connected mode, let alone receive any of the packets.

What could be the reason behind this? Essentially, I want to be able to wake up the device from the server. 

I am using Onomondo MVNO and the SIM has static IP address behind a VPN. The actual network is One Hungary, with the PTW being 2.56s. Edit: using LTE-M.

Thanks,
Mark

[Achim Kraus]

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.

[Mark Szente]

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...

[Mark Szente]

Only eDRX, not using PSM. 

[dejans]

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

[Mark Szente]

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

[Achim Kraus]

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.   

[Mark Szente]

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

trace-2025-06-13T12-37-54.224Z.mtrace

[dejans]

Hi,

Thank you for providing your modem trace.

Which modem firmware version do you use?

Best regards,
Dejan

[Achim Kraus]

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.