Cannot use promiscuous sample to capture Wi-Fi packets under station mode

[Muhammad Abdullah Jean]

Hello! I am using the nRF7002 in promiscuous mode to capture Wi-Fi traffic. Everything went smooth in AP mode where we use another nRF7002DK as a transmitter and our computer as a receiver to transmit data. I can capture all the QoS packages from that 7002 board, and the length is 1190 Bytes.

When using station mode, at the beginning of the capture, I can see several dozen QoS Data frames, but after that I only receive beacons, broadcast/multicast frames, and control frames. I also tried to reset the transmit board and start the transmittion again, but no data frame was captured.

BTW I'm using v3.0.1SDK and toolchain for your reference.

I would like to know why the QoS Data frames only appear for a short time and then stop, and whether there is any recommended way to keep receiving them continuously.

Thanks!

[Amanda Hsieh]

Hi,

Are you sure that you are operating in the Promiscuous mode ? Or do you mean Monitor mode? I'm asking since Promiscuous mode is not expected to work in AP mode, where you say it is working fine. Promiscuous mode is expected to work only in Connected Station mode and is expected to capture frames only from the BSSID to which it is connected.

More details can be found in the documentation at :

• Promiscuous mode: https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/protocols/wifi/advanced_modes/promiscuous_op…
• Monitor mode: https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/protocols/wifi/advanced_modes/sniffer_rx_ope…

Regards,
Amanda H.

[Muhammad Abdullah Jean]

Hello, thanks for your reply!

I 'm sure I am using promiscuous mode since I have enabled 'CONFIG_NRF70_PROMISC_DATA_RX=y' in prj.conf. And no commands about monitor mode are established.

You said that promiscuous mode is not expected to work in AP mode, but I can actually capture the packages which are transmitted from another 7002dk board working in AP mode to a computer. I think perhaps it is because my promiscuous board works as a client in station mode? And it is not possible to enable promiscuous mode for the AP mode transmitter?

Btw I would like to ask whose RSSI am I actually measuring? Is it the RSSI of the packets received by the promiscuous board from the transmitter, or the RSSI from the router?

My previous understanding was that the RSSI captured by the promiscuous board comes from the packets transmitted by the transmitting board. Regardless of whether in AP mode or STA mode, the closer the promiscuous board is to the sender, the higher the RSSI will be.

Therefore, when testing in AP mode, the promiscuous board should be placed as close as possible to the computer network card of the receiver. In STA mode, the promiscuous board should be placed as close as possible to the router. The reason for doing this is that we want to study the signal strength transmitted by the capsule (transmitter), while the signal strength from the router to the receiver cannot be quantitatively controlled. Thus, we focus on the link from the sender to the router, i.e., the signal strength received at the router.

Is this understanding correct?

Thanks again for your help!

Best regards,

Jean

[Amanda Hsieh]

Hi, 

Muhammad Abdullah Jean said:

Is this understanding correct?

Promiscuous mode is only supported when the device is operating as a connected Station (STA), not as an Access Point (AP). See Promiscuous mode operation: "Promiscuous mode of operation is only supported in connected Station mode." 

Muhammad Abdullah Jean said:

Btw I would like to ask whose RSSI am I actually measuring? Is it the RSSI of the packets received by the promiscuous board from the transmitter, or the RSSI from the router?

The RSSI you measure is the signal strength of the packets received by your promiscuous board from the transmitter. See Promiscuous mode receive packet metadata. 

...

For accurate measurement of a transmitter's signal, place your promiscuous board close to the transmitter.

-Amanda H.

[Ziyao Zhou]

Hi,

I am also quite curious about this problem:

 

You mentioned if I have four devices, a transmitter working in STA, a router connected to the transmitter, receiver and promiscuous board. The RSSI in wireshark is the one from the transmitter to my promiscuous board. But What is modulation index? Should it be the index from transmitter to router. Or Should it be the index from router to receiver.

Then how about the transmitter is working on AP mode. The RSSI should be the one from the transmitter to my promiscuous board the same? And how about the MCS, is it the one from transmitter to promiscuous or transmitter to receiver?

Thank you so much!

[Amanda Hsieh]

RSSI in Wireshark is the signal strength of the received packet on the sniffer/promiscuous board.  The Modulation and Coding Scheme (MCS) index is a list of modulation schemes and coding schemes that are currently used to send data from WiFi devices (transmitters).

[Ziyao Zhou]

Thank you!