How does OPPO dual-card mobile phone switch traffic?

Take OPPO R9S mobile phone as an example, and the switching mode is as follows:

First, click the "Settings" icon on the desktop of OPPO R9S mobile phone to enter.

2. After entering the settings, select the "Dual Card and Mobile Network" option.

Third, find the "Internet access" item under the default card settings, and click Enter.

Fourth, check the SIM card that will use Internet traffic after entering.