Unusually low speeds in ECM mode compared to MBIM on RM520N-EU

IoT Modules 5G Module
1

I am experiencing unusually low transfer speeds when module is configured in ECM mode (AT+QCFG="usbnet",1). I’m seeing about 240-260Mbps downlink maximum. When changing to MBIM (AT+QCFG="usbnet",2), I see 600-700Mbps downlink. Uplink remains about same (100-120Mbps) in both modes. In both cases I am connected to Windows machine and performing test in same manner. In both cases I am utilizing same APN configuration. Signal quality remains identical between tests (-72 RSRP, 26 SINR, -10 RSRQ for NR5G). Is this expected behavior? It might be worth to note that speed achievable via ECM varies depending on time of day in a same way speed over MBIM varies, just that ECM speed seems artificially lowered somehow.

I was hoping to utilize these modules in small production (about 4-5 units) of embedded/industrial routers with ethernet port exposed via RTL8125BG and USB lanes connected to low power ARMv7 SoC for control plane utilizing AT commands and QMAP for multi-connection, allowing for remote access to devices behind NAT remotely via control plane. Essentially, I am hoping to utilize IPA offload as hardware NAT solution.

It is my current understanding, that both ECM as well as ethernet driver utilize QMAP for connection and IPA for traffic offload, so speeds should be comparable between both.
For reference - I am seeing same speeds on development board when configured for RTL8125BG and in the process of debugging this problem I have decided to remove any potential variables ethernet introduces.

Module details:

OC: RM520NEUDA-M20-SGASA
SW: RM520NEUDAR03A06M4G_01.201.01.201

Current active MBN profile is “Orange_Poland_Commercial”.

2

It is normal. For RM520N MBIM has better performance than ECM.
If higher performance is required, we even recommend connecting another PHY to the RM520N.
ECM network card mode will go through the module NAT. It is not somehow Hardware NAT, ECM is actually the dial-up on the AP side inside the module, which is then forwarded through the router, and of course the same is true for Ethernet.

3

Does that mean that PHY gets NAT offload via IPA but ECM does not, despite both having dial-up on AP side?

For reference, I’ve checked system load during prolonged test with AT+QUPTIME and the result was load average: 0.32, 0.24, 0.25.