RUTX50 RG501Q-EU USB/modem crashes on RutOS 7.23/7.24 – stable on 7.22.4

Networking Solutions Issue
1

Hello,

I would like to report a recurring internal modem issue on my RUTX50. I have done several tests with different RutOS versions and another Teltonika router, and the results seem to point to a regression somewhere between RutOS 7.22.4 and 7.23.x, or possibly an interaction between the newer software/kernel and the internal RG501Q-EU modem.

Device information

  • Device: Teltonika RUTX50

  • Hardware revision: 0202

  • Batch: 0018

  • Internal modem: Quectel RG501Q-EU

  • Modem firmware: RG501QEUAAR12A11M4G_04.202.04.202

  • Original Teltonika power supply

  • Mobile operator: Magenta Austria

  • APN: business.gprsinternet

  • Low signal reconnect: disabled

  • No automatic reboot/reconnect rules configured

The router itself does not reboot when the problem occurs. Only the internal modem/mobile connection fails.

Original problem on RutOS 7.24.1

With RUTX_R_00.07.24.1, the mobile connection repeatedly dropped.

The important point is that this was not just a normal loss of mobile registration or PDP connection.

During the failures, the internal RG501Q-EU actually disappeared from the router’s USB bus.

Typical log messages were:

ttyUSB0 ... disconnected
ttyUSB1 ... disconnected
ttyUSB2 ... disconnected
ttyUSB3 ... disconnected

qmi_wwan ... wwan0: unregister

xhci-hcd ...
usb 2-1: reset SuperSpeed USB device

Write to modem failed: errno 5
Failed to send command

Modem `2-1 [2c7c:0800]` is not responsive!

In some occurrences I also saw messages such as:

xhci-hcd: ERROR: unexpected setup address command completion code 0x11
usb 2-1: device not accepting address ..., error -22
usb 2-1: USB disconnect

RutOS then power-cycled/recovered the modem, the modem reappeared as a USB device, and the mobile connection was restored.

These crashes sometimes happened after only a few minutes and sometimes after approximately 20–30 minutes.

RAM / Tailscale investigation

Initially I also found an out-of-memory event in one troubleshoot file. tailscaled was using a considerable amount of RAM, so I investigated this separately.

However, later modem crashes occurred with:

  • approximately 50% RAM usage

  • no OOM event

  • Tailscale not running

  • modem temperature approximately 45–48 °C

The exact same USB/modem failure still occurred.

For that reason, I do not believe RAM exhaustion or Tailscale is the root cause of the modem disconnects.

Test with RutOS 7.23.7

I downgraded the router to:

RUTX_R_00.07.23.7

The configuration was recreated cleanly and only the necessary services were configured.

Unfortunately, the same type of hard modem failure occurred again.

After one clean boot, the internal modem failed after approximately 28 minutes.

Again the logs showed the same general sequence:

ttyUSB... disconnected
qmi_wwan ... unregister
USB/xHCI errors
modem not responsive

A further dropout occurred only a few minutes later.

I therefore upgraded back and concluded that the problem was not specific to RutOS 7.24.1.

Comparison with another router

For comparison, I removed the RUTX50 and connected my Teltonika RUTM54 using the same SIM card at the same location.

The RUTM54 remained stable without mobile disconnect events.

The signal quality at this location is generally good/excellent. Depending on band and antenna configuration, I have seen approximately:

  • LTE RSRP around -70 to -80 dBm

  • good LTE SINR, often around 20 dB

  • 5G n28 also available

I use two external mobile antennas and two antennas directly on the router.

This comparison makes a general SIM/operator problem less likely.

Test with RutOS 7.22.4

I then downgraded the RUTX50 further to:

RUTX_R_00.07.22.4

Again, I performed a clean configuration and initially installed only the necessary settings.

This test has produced a very different result.

The router has now been running for approximately:

3 days 19 hours

without a single occurrence of the previous hard USB/modem crash.

There was one short mobile connection interruption after approximately 19 hours, but the log showed a completely different failure mode.

The modem briefly changed network registration state:

Network registration status: Searching
Network registration status: Registered, home

and the mobile data session was re-established shortly afterwards.

Importantly, during this event there was:

  • no ttyUSB disconnected

  • no qmi_wwan unregister

  • no xHCI error

  • no USB disconnect

  • no Modem is not responsive

  • no modem power-cycle

The RG501Q-EU remained present and responsive on the USB bus.

Therefore I consider this event a normal mobile/network reconnect and not the same issue as the failures seen on 7.23.7 and 7.24.1.

Since then, the connection has remained continuously stable.

Current observation

So far my results are:

RutOS 7.24.1

Repeated hard internal modem/USB crashes.

RutOS 7.23.7

Same hard internal modem/USB crashes.

RutOS 7.22.4

Currently approximately 3 days 19 hours without a hard modem/USB crash.

RUTM54 with same SIM/location

Stable.

This makes me suspect that something changed between the 7.22.x and 7.23.x branches that affects the RG501Q-EU or its USB/xHCI communication.

I understand that correlation does not necessarily mean that RutOS itself is the root cause, but the difference between the versions is significant enough that I would appreciate further investigation.

Questions

Could Teltonika please advise:

  1. Were there any kernel, xHCI, USB, QMI or RG501Q-EU related changes between RutOS 7.22.4 and 7.23.x that could explain this behaviour?

  2. Is this USB disconnect / qmi_wwan unregister / ttyUSB disconnected behaviour known with the RG501Q-EU?

  3. My modem currently runs:

    RG501QEUAAR12A11M4G_04.202.04.202

    Is there a newer modem firmware recommended and officially compatible with hardware revision 0202 / batch 0018?

  4. I have seen references to:

    RG501QEUAAR12A11M4G_04.300.04.300

    on other RUTX50 devices. Is this firmware compatible with my unit, and could it be provided or enabled through the modem firmware updater if appropriate?

  5. Could the difference between 7.22.4 and 7.23.x indicate a kernel/USB driver regression rather than a hardware defect?

  6. If required, I have complete troubleshoot .tar.gz files captured immediately after the failures on the different RutOS versions and can provide them privately.

I would prefer not to upload the troubleshoot archives publicly because they contain device/network information, but I am happy to provide them directly to Teltonika engineers.

Thank you for your help,
Harald

3

Hello,

For troubleshooting purposes, we will require more sensitive information from your end, such as the troubleshoot file, which may contain passwords, public IP addresses, serial numbers, and such. To avoid leaking this information, we have sent you a form to fill out, which you will receive in your e-mail inbox that you have registered your account with in the forums. In the Ticket ID field of the form, please enter the ID of this thread, which is 20814.

Best Regards,
Z.