NR5101 loses internet connection when getting a call

bastigrun Posts: 6
First Comment
edited March 11 in Mobile Broadband

When the SIM card in my NR5101 is getting a regular voice call, it most of the time loses internet connection. It doesn't loose cell coverage, the whole router just stops connecting to the internet and it also doesn't reconnect when the call is over. It's a multi SIM setup with 2 SIM cards working at the same time. One in the router, one in my mobile phone. The call (if I take it) works fine, but the router is dead and needs a reboot.

Which of course is bad, because all that needs to happen to sabotage my internet connection is ringing me on that number: My mobile phone rings, my router crashes.

I can still login into the web-interface, though. The web-interface doesn't show any problems and considers the connection to be up. The router itself is blinking red. The mobile phone doesn't have any issues at all and stays connected with 5G or 4G all the time.

Otherwise, connection is very good.

Any ideas?

All Replies

  • bastigrun
    bastigrun Posts: 6
    First Comment
    edited March 12

    I can now confirm this behavior by calling the SIM card in the router. (Update: I first thought, this was only true for certain calls from certain providers, but I now was able to reproduce it with pretty much any phone/SIM card or provider).

    This is the behavior I can reproduce:

    Whenever someone is calling the SIM card in my NR5101 device AND the device is sending/receiving datastreams in the 5G network at the same time (like I having a zoom conference via the NR5101 internet connection and then someone calls the SIM card) the NR5101 freezes in the exact millisecond the call comes in. If there's no data transfer during this millisecond, the NR5101 keeps the internet connection, no matter how long the call is ringing or whether I take the call on a multisim on another device or not.

    I can reproduce it by opening up a video conference and calling my number from any phone now. I'm pretty sure it's a freeze because I already waited approx. 8 hours for the router to come back up but nothing changed, only a disconnect from the power network and complete reboot helps.

    This is obviously an unwanted behaviour and might be security risk as well, especially as the router admin and some ports are still active (but it doesn't save any settings). People with knowledge would also be able to sabotage internet connections by call-bombing a SIM card in an NR5101 device with no way to bring it back up as long as not somebody or something disconnects the router from the power supply for some seconds and then waits for it to reboot. This actually already crashed several of my video conferences (that's why I noted it).

    So either my router is broken or there's a bug. Would be interesting to hear if some other people have seen similiar undesired behavior or can reproduce it.

    I tried to look at the logs, but in the router menu, there's nothing saved in the log section. Is this normal? I have not checked log files on the device via SSH, yet, though.

    The only solution that comes to my mind for me now to solve that issue is trying to convince my provider to block calls to that particular SIM card and then try again. Which is not a good solution for me because I use the SIM card for getting calls sometimes, too.

  • tonygibbs16
    tonygibbs16 Posts: 836  Guru Member
    First Anniversary 10 Comments Friend Collector First Answer
    edited March 13

    Hello @bastigrun

    Welcome to the forum.

    I don't work for Zyxel, but are you able to say what firmware release you are running in your NR5101 please?

    Kind regards,


    PS: with a completely different Zyxel product, I had an experience where an incoming landline call would disconnect my DSL connection. I resolved it when I upgraded the firmware on the Zyxel product.

  • bastigrun
    bastigrun Posts: 6
    First Comment

    I am currently running V1.00(ABVC.9)D0.

    I had the same issues with the firmware before that, though.

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