https://blog.wongcw.com/2019/03/13/2g%e3%80%813g%e8%a6%81%e9%80%80%e7%b6%b2%e7%94%a8%e6%88%b6%e6%89%8b%e6%a9%9f%e9%82%84%e8%83%bd%e6%ad%a3%e5%b8%b8%e4%b8%8a%e7%b6%b2%e5%92%8c%e6%89%93%e9%9b%bb%e8%a9%b1%e5%97%8e%ef%bc%9f/