RM500Q-GL uplink issue

Hi Community,

I am facing an issue with several Quectel RM500Q-GL connected to a 5G SA network. In particular, when I start an iperf between the device and the 5G node, the communication seems good for some minutes before stopping the data exchange. Here, the data (DRBs) are not sent anymore from the device but signalling (SRBs) is correctly sent to the 5G gNB. In the DL, this behavior is not detected and the communication works smoothly.

Could it be an issue in the Quectel firmware of the RM500Q-GL. Indeed, I am also using a OnePlus8 connected to the network (same Qualcomm chip-set of the RM500Q-GL) and it properly works.
Do you have any suggestions?

Thank you.

Performing some test, I discovered that TCP UL communication seems to work, while UDP UL stops as described in the previous post. Thus,I am wondering if we need to “acknowledge” somehow the communication with Quectel to make it works.

@herbert.pan-Q in this comment you suggest that a heartbeat is necessary.

Could you please let me know if my hypothesis is correct?


Is the current problem occurring at RM500QGL?

Yes, the problem is occurring with RM500Q-GL, fw version RM500QGLABR11A06M4G.

I am still testing the communication for both DL and UL. In DL it correctly works while in UL only TCP works and UDP stops working after a while.

I was able to capture the packet at MAC-NR level. When it stops working in UDP mode, the Quectel starts to send short Buffer Status Reports (BSRs) in UL-SCH with Buffer Size (BS) = 0. However, before failing, BS is always >= 0 which means that the device is sending data.
Even if the device is not sending data anymore, the SRB (Signalling Radio Bearers) are always sent and the MAC scheduling works as expected. Overall, the device continues to be attached to the network and all the control plane procedures correctly work.

Please let me know if you need further information to find the issue.


@herbert.pan-Q some updates about latest tests.

In TCP mode, I have some issues about synchronization between gNB and Quectel. This synchronization lack causes many TCP retransmission and it triggers RA procedures even if the UEs are already connected (most probably it may happen something like handover, where data are exchanged between the UE and the source node while the UE performs a RA procedure with target node).

Thus, to confirm the hypothesis about acknowledged communication, I started a test with UDP in UL and an acknowledge mechanism that allows for some DL data exchange. In this case, also UDP works while in the previous tests it shown the issues described in the first post.

Honesty speaking, I am starting to feel that there is bug in the firmware version RM500QGLABR11A06M4G. I am wondering if I can have the source code of the firmware to check if I might be right.
Is it possible for you to share the fw code of the RM500Q-GL? If not, could you please verify that my concerns are correct?

I am guessing that you may be the right person to discuss this kind of issue. If I am wrong, could you please provide me with the contact of the one responsible of these topics?

Thanks a lot.

Any news on this topic? I acquired several RM500Q modules and I need to know if there are issues with them. Please let me know any information that may help.