Car wifi is the free wifi provided by the car above, which belongs to the wifi provider company, is the purchase of wifi equipment, in general, unlimited traffic. You need to accept a verification code to enter.
If you want to install in-car wifi, you need to buy equipment. Traffic can be unlimited, different network service providers are different prices, according to the package charges.
example
If you have a China Telecom Tianyi 3G UIM card,
You plug it into the wireless router you bought (just like inserting a SIM card into a mobile phone), then turn on the router, and when the router receives the 3G signal of the telecom, it will automatically convert to WIFI signal, and all your Wifi-enabled devices can be connected to the Internet (of course, you can encrypt the router or change the password, which is usually encrypted by default).
This wireless router with a mobile phone lithium battery as a power source, generally available for about 2-3 hours. You can also buy a car USB charging cable with MINI USB port for easy use in the car. The price of this kind of product is around 200 to 400.