https://blog.gongquiz.com/2022/09/30/osi-7%ea%b3%84%ec%b8%b5-%eb%aa%a8%eb%8d%b8-%ec%a4%91-1%ea%b3%84%ec%b8%b5%ec%97%90%ec%84%9c-%eb%8f%99%ec%9e%91%ed%95%98%eb%8a%94-%ec%9e%a5%eb%b9%84%eb%a1%9c-%ec%98%b3%ea%b2%8c-%eb%82%98%ec%97%b4/