https://qooah.com/2011/12/29/ntt-docomo-%e6%97%a5%e9%9f%93%e8%81%af%e6%89%8b%e5%90%88%e8%b3%87%e7%a0%94%e7%99%bc%e6%89%8b%e6%a9%9f%e6%99%b6%e7%89%87/