https://blog.gongquiz.com/2022/09/22/osi-%ec%b0%b8%ec%a1%b0-%eb%aa%a8%eb%8d%b8%ec%9d%98-%ea%b5%ac%ec%84%b1%ec%9a%94%ec%86%8c-%ec%a4%91-%ec%84%9c%eb%b9%84%ec%8a%a4%ec%99%80-%eb%8d%b0%ec%9d%b4%ed%84%b0-%eb%8b%a8%ec%9c%84%ec%97%90-%eb%8c%80/