RUTX50 - new 5G SA connection not working

davyjones · February 15, 2025, 5:37pm

Today I purchased a SIM from an ISP here in Finland that supposedly is now offering 5G SA (Standalone) as a SIM only plan without having to also purchase their equipment.

The sales person informed me this is a 5G SA connection however when place the SIM in the RUTX 50 I don’t get a 5G only option and if I set the connection so be SA then it defaults to 4G LTE like my previous 5G NSA (Non Standalone) SIM from another ISP.

And the RUTX 50 software UI is also prompting something about MTU 1280 or 1500 on the new connection and I don’t know what this means exactly.

So I am thinking either this is not actually a 5G SA (Standalone) plan, I have wrong settings or perhaps the device requires an external antenna to actually get 5G only and 5G SA connnection. If anyone could offer some advice I would appreciate it.

davyjones · February 16, 2025, 8:45am

Update: I was able to configure the connection to use 5G only by selection LTE bands that are not available so it’s now running in SA mode it seems but there is still no 5G only network type selection.

Is there some kind of configuration script I can run to get it to lock to 5G N78 and ignore all else or something like that?

Daumantas · February 17, 2025, 8:41am

Hi @davyjones ,

Preferred network type is usually controlled by the operator or SIM card. Have you changed to 5G SA plan and kept the old SIM? It might be that you need to replace it for the preferred network type to be 5G SA.
However, if this device is stationary, you can select 5G NR-only mode by navigating to System → Troubleshoot, and in Modem debug section run this AT command:

AT+QNWPREFCFG= "mode_pref",NR5G

This change will likely be overwritten once the device is rebooted or mobile connection is re-established, thus I would also suggest placing this command in custom scripts:

gsmctl -A 'AT+QNWPREFCFG= "mode_pref",NR5G'

Best regards,

davyjones · February 17, 2025, 8:54am

Hi, no it’s a completely new SIM as it’s from a different ISP. And yes the device is stationary. I will try those commands and report, thanks!!

davyjones · February 17, 2025, 4:17pm

I have added the custom script after I added the latest firmware.

Some how the device seems to be in an add MTU 1280, then MTU 1500, the MTU 1280 endless loop now.

I had these prompts after I first inserted the new ISP 5G SA SIM, I then set 1280 and then it prompted to add 1500 and the once the connection restarted the prompts disappeared. Now it seems to continue for some reason, odd.

davyjones · February 17, 2025, 7:57pm

Nevermind, the MTU endless loop appears to have calmed down now. Or at least it’s not presenting the MTU 1280 or 1500 messages anymore.

It’s now running at 5G SA based on these connection settings. I understand the point that the connection options will be based on what the operator provides but was the script suggestion supposed to offer a Preferred network type of 5G only?

Daumantas · February 18, 2025, 6:11am

Hello,

The script was offered as a suggestion to lock the device to 5G SA.
It could be that some sort of caching mechanism is now in place and the device will connect to SA network on it’s own. Could you try selecting 4G-only → Save and Apply → change to 5G/4G/3G auto → Change preferred network type to SA and check if the device connects to SA on it’s own?

Best regards,

davyjones · February 18, 2025, 12:39pm

Thanks, this was interesting. I tried it and the first time it did not switch to 5G SA on it’s own so I started to take screenshots to record the process but then I repeated the same process again and it did.

davyjones · February 18, 2025, 6:10pm

Random questions if I may ask.

Since the router can now be running in 5G SA mode even though the following is applied,
Preferred network type: 5G/4G/3G auto
does it technically mean that than it’s in 5G only mode and that is how 5G only in applied in this case.

And I came across another post on the forum here listing the following CLI command to check the operator’s MTU vs what has been applied in the router. Based on what I have applied below are these command results valid?

Network > WAN > WAN interfaces > mob1s1a1 > Advanced Settings > Override MTU: 1500

root@RUTX50:~# gsmctl -A at+qmtuinfo
+QMTUINFO: 1,1500,1280

Daumantas · February 18, 2025, 8:48pm

Hello,

Generally it’s best to check MTU by just using the internet - if you don’t experience any strange issues with certain sites (for example, only Netflix is buffering constantly, while text-based sites are okay) and if everything is working - leave it on 1500. I would be surprised if a modern 5G SA network uses MTU of 1280, as I’ve only seen it on some older networks. Since SA is still relatively uncommon, it may be that the modem interprets operator advertised value incorrectly or RutOS parses it incorrectly (although I haven’t seen any similar reports of this).
Let me know if you experience any further issues!

Best regards,

flebourse · February 18, 2025, 9:01pm

A MTU of 1280 bytes doesn’t seem to be uncommon, at least for IPv6:

root@lgr5g:~# gsmctl -A 'AT+QMTUINFO'
+QMTUINFO: 1,1500,-
+QMTUINFO: 2,1500,1280

davyjones · February 19, 2025, 8:46pm

I have also been discussing this on the forum of the ISP providing the 5G SA connection. And someone there noted the following which was interesting.

i have teltonika TRB500, so thing are not same. but i have 5g only option and i can also select NSA and SA. but i cannot select 4g/5g mixed, which i think is bad. i haven’t test elisa sim card on TRB500.

I have 5G SA running based on the following so all seems otherwise okay so long as I start with as you suggested above, switching to 4G only, then the 5G mixed mode+SA and then it will connect.

Preferred network type: 5G/4G/3G auto
5G mode: SA
Band selection: Auto

Network type: 5G (SA)
Bands: 5G N78

I was wondering though is a “5G only” option an actual option inside the router OS or does it render dynamically based on what the connection is telling the device or the method above that I have, i.e. 5G mixed mode+SA is techically the same as 5G only?

iBoucher · February 19, 2025, 9:01pm

@davyjones ask that person which RUTOS version he have. Most possibly, it will be quite old, as previously this 5G only was available, but it was removed as it confuses users - when 5G only was selected, only SA mode could work, but some users didn’t know that ant expect 5G NSA mode which uses 4G too. That’s why 5G only was removed and 5G network mode selection was introduced.

davyjones · February 19, 2025, 9:44pm

Ah ok, thank you as this I did not know about

davyjones · March 18, 2025, 10:31am

@Daumantas I wanted to provide a sort of longer term update here should it help anyone else experiencing the sames issues as I.

I had things working for 5G SA on the RUTX 50 until it came to a point where some clients could not connect and over ethernet could not even acces the admin console. Anyway so I just factory reset and the device seemed to set itself up for 5G SA without any settings added by me.

And I was planning to reply here telling about the above until I noticed yesterday some connection issues and when I logged into admin it was running on 5G NSA. I tried setting the 5G mode to SA but it did not help so I added the command above to Custom Scripts, rebooted and that seemed to fix things. So the point being that unless I used that command the device not seem to use 5G SA and that is what my ISP plan supports. So just to note that if it helps at all.

And side note - when on 5G SA the RUTX 50 connects to a single 5G frequency so is this normal behaviour? I mean since I am using the default setup without any external antenna or something like that. And would the RUTM52 (and no I’m not looking to upgrade anytime soon ) with dual modem, more antennas and better CPU connect to more bands in a similar configuration and bascially offer better connection peformance.

iBoucher · March 18, 2025, 5:43pm

Hello,
Yes, RUTX50 is available to have only one band on 5G SA. RUTM52 have different modems which are capable to have more than one band on 5G SA.

davyjones · March 21, 2025, 8:09am

Hi, I checked the RUTX50 for 5G SA status this morning and noticed that it was connected to 5G N28 not 5G N78 and the performance seemed a lot less.

I modified the WAN MTU from 1280 to 1500 and restarted the connection and it switched back to 5G N78 and I then placed the MTU back to 1500.

I have a Startup script running to make sure that 5G SA is maintained since Network > Mobile > Connection settings are not sufficient or so I have found. Or maybe they are and it is my ISP that is the issue.

# Put your custom commands here that should be executed once
# the system init finished. By default this file does nothing.

gsmctl -A 'AT+QNWPREFCFG= "mode_pref",NR5G'

exit 0

And when running on 5G N78 the connection details are as follows

root@RUTX50:~# gsmctl -A 'AT+QCAINFO                                                                                                                          
> ^C                                                                                                                                                          
root@RUTX50:~# gsmctl -A 'AT+QCAINFO'                                                                                                                         
+QCAINFO: "PCC",641280,12,"NR5G BAND 78",155

So could someone help me to create the syntax to add to the Startup script so I can lock the device on 5G SA and the 5G N78 band? I understand it should be something like the following but I am not sure of the parameters required.

gsmctl -A '+QNWLOCK: "common/4g",2,6400,354,6400,348'

And then the Startup script would look something like this, again I am not sure of the required syntax

# Put your custom commands here that should be executed once
# the system init finished. By default this file does nothing.

gsmctl -A 'AT+QNWPREFCFG= "mode_pref",NR5G'

gsmctl -A '+QNWLOCK: "NR5G BAND 78",<num of cells>,[[<EARFCN>,<PCI>],...'
exit 0

davyjones · March 23, 2025, 10:46am

I realised later that I can of course just use the UX to lock to 5G SA N78 and don’t need a console command at all. What’s confusing is that I still need to select at least 1 x LTE/UMTS band and I don’t know if the startup script is still needed now either since I’m no longer using Auto. Anyway it functions as expected for now…

Daumantas · March 24, 2025, 4:58am

Hi @davyjones ,

The selection in the WebUI still allows the router to fall back to 4G or 3G (thus the band selection). In essence, it is the same as full auto, but the device can only connect to 5G SA, and not NSA.
My provided command only allows the device to connect to 5G SA, and it won’t be able to fall back to 4G or 3G.

davyjones · March 24, 2025, 7:55am

Okay thanks. So based on that webUI selection when 5G SA is not available it would fall back to 4G or 3G. But the command you provided below in system/maintenance/uscripts prevents the fall back option. And then based on N78 selection in the webUI it should stay locked to N78.

gsmctl -A 'AT+QNWPREFCFG= "mode_pref",NR5G'

exit 0