[TCP三次握手](TCP%E4%B8%89%E6%AC%A1%E6%8F%A1%E6%89%8B.md) [OSI7层](OSI7%E5%B1%82.md) [http状态返回码](http%E7%8A%B6%E6%80%81%E8%BF%94%E5%9B%9E%E7%A0%81.md)