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8821cu-20210916/docs/Concurrent_Mode.md

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2022-12-27

What is Concurrent Mode?

Concurrent Mode creates 2 wireless network interfaces (wlan0, wlan1) and those two interfaces share the same WiFi adapter.

This feature allows performing 2 separate wireless tasks at the same time with a single WiFi adapter.

For example:

Use station mode (also called managed or client mode) to connect with an AP to access the internet at the same time as it also performs as an AP to allow other devices to connect to the second interface.

Note: Only supports 3 combinations

  1. Station mode + Station mode
  2. Station mode + AP mode
  3. Station mode + P2P mode

Note: Monitor mode is not supported.

How do I Enable Concurrent Mode?

Edit the Makefile with a text editor:

${EDITOR} Makefile

Change the following line:

#EXTRA_CFLAGS += -DCONFIG_CONCURRENT_MODE

to

EXTRA_CFLAGS += -DCONFIG_CONCURRENT_MODE

and then install the driver per the installation steps. If the driver is already installed, run the following first:

sudo ./remove-driver.sh

and then reinstall the driver with:

sudo ./install-driver.sh

Once the driver is fully installed and you have rebooted the system, you can verify that this works by typing the “iw dev” command. You should see two wireless interfaces, and the MAC address of the secondary interface is nearly the same as the first except for one digit.

FAQ:

Q: Which wireless interface can run in station mode? Which wireless interface can run in AP mode?

A: It is recommended to run station mode in wlan0 and AP or P2P mode in wlan1.

Q: How is the throughput with 2 wireless interfaces in concurrent mode?

A: Because there is only one physical hardware device, the two wireless interfaces (wlan0, wlan1) will share the transmit bandwidth.

For example:

Assume the throughput limitation of current environment is 85Mb/s, then the throughput of wlan0 + the throughput of wlan1 is basically equal or smaller than 85Mb/s.

Q: Everything is fine when I only start hostapd, but when I start running station mode in the other interface at the same time, hostapd will disconnect for a moment then will reconnect again, however ,the channel is differ from before. Is something wrong?

A: Don’t worry, it is fine! As mentioned before, those two wireless interfaces share the same physical hardware device. That means those 2 wireless interfaces must use the same channel. The AP/P2P interface should use the same channel as the station interface. If both interfaces are running in station mode, the connected APs MUST be on same channel.