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TCP的握手、挥手。为什么是三次握手而不是两次?为什么是四次挥手而不是三次 #158
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握手三次 确保通信双方的接收和发送能力都是正常的 |
三次握手 确保客户端和服务端都有接受数据和发送数据的能力。 |
由于tcp是双工连接,三次握手保证了双方的接受和发送能力,四次挥手是因为在客户端发送资源完成给服务端后,服务端必须返回ack确认,但是服务端关闭资源处理需要时间,所以会再次发送关闭。 |
三次握手其实就是指建立一个TCP连接时,需要客户端和服务器总共发送3个包。进行三次握手的主要作用就是为了确认双方的接收能力和发送能力是否正常、指定自己的初始化序列号为后面的可靠性传送做准备。实质上其实就是连接服务器指定端口,建立TCP连接,并同步连接双方的序列号和确认号,交换TCP窗口大小信息。第三次握手是为了防止失效的连接请求到达服务器,让服务器错误打开连接。 |
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