从一个HTTP请求来读懂HTTP、TCP协议

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"从一个HTTP请求来看网络分层原理"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"两台主机间会通过非常多网络设备，不管哪个网络设备都会发生数据丢失，如果发生数据丢失的话，会发生数据重传，会出现数据重复(之前丢失的包并不是丢失而是产生了延时)。数据传输的介质也可能多样，如内网里通过网线进行传输，连接到公网的话会通过光纤进行连接，所以要实现不同介质间信号的转换，还有从光纤到路由器无线脉冲转换，距离远的话还有信号衰减问题。所以在网络传输过程中有非常多的问题需要解决，把问题分组分层，不同层次间解决不同问题，不同层次间定义标准化接口让它们间可以进行数据的通信。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"复杂的网络"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s2.51cto.com/oss/202010/20/2ca881c90ac1021517ea89c524ddd692.png-wh_600x-s_379608925.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/89/898d19e0668f3b2d5ce640b5c293f186.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s2.51cto.com/oss/202010/20/2ca881c90ac1021517ea89c524ddd692.png-wh_600x-s_379608925.png","title":null}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"为了简化网络的复杂度，网络通信的不同方面被分解为多层次结构，每一层只与紧挨着的上层或者下层进行交互，将网络分层，这样就可以修改，甚至替换某一层的软件，只要层与层之间的接口保持不变，就不会影响到其他层。"}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"OSI( Open System Interconnection Reference Model): 开放系统互联参考模型"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TCP/IP 协议族"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"OSI七层理论体系结构"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s6.51cto.com/oss/202010/20/cce1692da335fa5d2dde2a8a30f93227.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/e7/e723e4d74254b14ae715a21e7f3abdd6.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s6.51cto.com/oss/202010/20/cce1692da335fa5d2dde2a8a30f93227.png","title":null}}]},{"type":"numberedlist","attrs":{"start":null,"normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"物理层："},{"type":"text","text":"解决两台主机的通信问题—A往B发送比特流(0101)，B能接收到这些比特流。定义了物理设备的标准如网线的类型，光纤的接口类型以及传输介质的传输速率等。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"数据链路层：由于物理层上的传输的比特流可能会出现错传、误传等，所以数据链路层定义了如何格式化数据即将比特流封装成帧，提供了错误检测。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"网络层："},{"type":"text","text":"随着节点的增加，点对点通信是需要经过多个节点的，如何找到目标节点，如何找到最优路径变成为了首要需求。所以出现了网络层，主要目的是将网络地址翻译成对应的物理地址，分组传输、路由选择，本层的传输单位是数据报(分组)，本层需要注意的TCP/IP协议中的TCP协议。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"传输层："},{"type":"text","text":"随着网络需要的进一步扩大，通信过程中需要传输大量的数据，网络可能会发生中断，为了保证传输大量文件时的准确性，需要对发送的数据进行切分，切分成一个个的segment进行发送，考虑如何在接受方拼接切分的segment组成完整的数据，以及发现丢失segment时该如何处理，需要注意的协议TCP、UDP。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"会话层："},{"type":"text","text":"不同机器上的用户之间建立以及管理会话。用于保证应用程序自动收发包和寻址。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":6,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"表示层："},{"type":"text","text":"信息的语义语法，加密解密，转换翻译，压缩解压缩。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":7,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"应用层："},{"type":"text","text":"规定双方必须使用固定长度的消息头，且消息头必须记录消息长度等信息。需要注意的是TCP/IP协议中的HTTP协议。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s2.51cto.com/oss/202010/20/7f70bcd8b566495c50709b65918b2708.png-wh_600x-s_3042196636.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/73/733b6578e18e8e4c3f4f1c3ee49d60c3.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s2.51cto.com/oss/202010/20/7f70bcd8b566495c50709b65918b2708.png-wh_600x-s_3042196636.png","title":null}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"TCP/IP四层模型"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"是OSI的一种实现，包括应用层、运输层、网际层和网络接口层。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s2.51cto.com/oss/202010/20/098fa5e287316c1fd52125b9112cb8e4.png-wh_600x-s_3103511319.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/76/76cb34519bd4344cb7fc86c2d0e7bc91.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s2.51cto.com/oss/202010/20/098fa5e287316c1fd52125b9112cb8e4.png-wh_600x-s_3103511319.png","title":null}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"一个HTTP请求的分层解析流程"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s2.51cto.com/oss/202010/20/eac5b8bcad9162d4ec75ccecf4c29ea8.png-wh_600x-s_3348559328.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f7/f752f69ead1f8d1e76e9e14bd55193c7.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s2.51cto.com/oss/202010/20/eac5b8bcad9162d4ec75ccecf4c29ea8.png-wh_600x-s_3348559328.png","title":null}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如上图右边一个服务器部署了一个静态页面，通过nginx部署在公网上，浏览器通过域名对它进行访问，浏览器输入域名点回车后是怎么工作的呢？"}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"http://www.dumain.com "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"服务端只认ip地址，浏览器将域名解析出来，看下浏览器里有没有域名对应DNS的缓存，有的话直接拿到服务端的ip地址，没有的话去本地的host文件看有没有配置，没有配置的话才会发起一个DNS请求用来获取服务器ip地址。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"DNS也是台服务器也有自己的ip地址，这时候应用层会构造一个DNS请求报文，应用层会去调用传输层的接口一个socket的API，DNS默认使用UDP实现数据传输，即应用层调用传输层的API，传输层会在DNS请求报文基础上加一个UDP的请求头，传输层将数据交给网络层，网络层同样在UDP请求报文基础上加IP的请求头，网络层会将IP请求报文交给数据链路层，数据链路层会将自己的mac头加上去并把对应的请求报文交给下一个机器的mac地址也会加上去，下一个机器的mac地址通过网络层ARP协议找到，ARP会发送一些请求看下你对应的ip地址的mac地址是多少，最后通过物理层物理介质传出去，通常传到路由器上."}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"路由器是三层设备(从下向上)从物理层开始连接，物理层交给数据链路层，数据链路层看下地址是不是给我的，是给我的进行解析，不是给我的就丢弃，报文再传给上面一层网络层，网络层把数据传到下一个路由器的地址是多少，会通过运营商的网络接口传到运营商的路由器上，运营商有自己的DNS服务器，如果配置的是运营商自己的DNS服务器的话会直接在这个DNS服务器里找自己对应的域名拿到对应的ip地址，也就是刚请求DNS报文地址，然后原路返回解析直到应用层拿到刚域名对应的ip地址，这样就可以进行HTTP请求报文的发送，再调用传输层协议是TCP参数，同样每到一层加头。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"HTTP"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"什么是HTTP?"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"超文本传输协议，是一个基于请求与响应，无状态的，应用层的协议，常基于TCP/IP协议传输数据，互联网上应用最为广泛的一种网络协议,所有的WWW文件都必须遵守这个标准。设计HTTP的初衷是为了提供一种发布和接收HTML页面的方法。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"HTTP特点"}]},{"type":"numberedlist","attrs":{"start":null,"normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"无状态：协议对客户端没有状态存储，对事物处理没有“记忆”能力，比如访问一个网站需要反复进行登录操作。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"无连接：HTTP/1.1之前，由于无状态特点，每次请求需要通过TCP三次握手四次挥手，和服务器重新建立连接。比如某个客户机在短时间多次请求同一个资源，服务器并不能区别是否已经响应过用户的请求，所以每次需要重新响应请求，需要耗费不必要的时间和流量。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"基于请求和响应：基本的特性，由客户端发起请求，服务端响应。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"简单快速、灵活。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"text","text":"通信使用明文、请求和响应不会对通信方进行确认、无法保护数据的完整性。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"HTTP协议版本已经演化到3.0版本，关于协议版本可以查看 快速掌握HTTP1.0 1.1 2.0 3.0的特点及其区别"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"HTTP报文格式"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"HTTP 协议的请求报文和响应报文的结构基本相同，由三大部分组成:"}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"起始行(start line)：描述请求或响应的基本信息"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"头部字段集合(header)：使用 key-value 形式更详细地说明报文"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"消息正文(entity)：实际传输的数据，它不一定是纯文本，可以是图片、视频等二进制数据"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其中起始行和头部的字段并成为 请求头 或者 响应头，统称为 Header;消息正文也叫实体，称为 body。HTTP 协议规定每次发送的报文必须要有 Header，但是可以没有 body，也就是说头信息是必须的，实体信息可以没有。而且在 header 和 body 之间必须要有一个空行(CRLF)。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s4.51cto.com/oss/202010/20/1a566786f4f87b134c732c45cca957cb.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/72/729ca82aac598f042a848f9ba59293f9.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s4.51cto.com/oss/202010/20/1a566786f4f87b134c732c45cca957cb.png","title":null}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"请求行报文格式"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s4.51cto.com/oss/202010/20/289db58a4e8ba25b6460fb0f44648815.png-wh_600x-s_2637844719.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f7/f71d705041c02d0b1887cd8d5fc19760.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s4.51cto.com/oss/202010/20/289db58a4e8ba25b6460fb0f44648815.png-wh_600x-s_2637844719.png","title":null}}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"请求方法:如 GET/HEAD/PUT/POST，表示对资源的操作;"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"请求目标:通常是一个 URI，标记了请求方法要操作的资源;"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"版本号:表示报文使用的 HTTP 协议版本。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"响应报文格式"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s6.51cto.com/oss/202010/20/2a016c6c4e954d755a429cc3edfdaba6.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/94/94c457bf22bcba348313c53c41493ede.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s6.51cto.com/oss/202010/20/2a016c6c4e954d755a429cc3edfdaba6.png","title":null}}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"版本号:表示报文使用的 HTTP 协议版本;"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"状态码:一个三位数，用代码的形式表示处理的结果，比如 200 是成功，500 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定一个报文段应该包含多少个字节。"}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"MSS: Max Segment Size, 默认 536byte 实际数据 "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" "},{"type":"link","attrs":{"href":"https://s6.51cto.com/oss/202010/20/6a32cd810c727c3d7a48ad34605a4927.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/77/77f3549184238d5b62c30b0e3b497acf.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s6.51cto.com/oss/202010/20/6a32cd810c727c3d7a48ad34605a4927.png","title":null}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在网络传输过程中可能会出现以下的一些情况："}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"客户端一段时间没有收到 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字段重排序，还需要丢弃重复包。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"数据传输的可靠性"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"停止等待协议如下： "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s3.51cto.com/oss/202010/20/3d92bc12b5c0a1681c07a7e83e38c0bf.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/77/77f3549184238d5b62c30b0e3b497acf.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s3.51cto.com/oss/202010/20/3d92bc12b5c0a1681c07a7e83e38c0bf.png","title":null}},{"type":"text","text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"停止等待协议，效率比较低"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"重传机制如下："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"ack 报文丢失"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d5/d5a3acdf585df89055dec51c6e2d8dd3.png","alt":"从一个HTTP请求来读懂HTTP、TCP协议","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"请求报文丢失"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f8/f84c5a0f47952b1ae629f5a81879cf3d.png","alt":"从一个HTTP请求来读懂HTTP、TCP协议","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"滑动窗口协议与累计确认(延时ack)"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如上效率低，所以tcp提出了新的协议-滑动窗口协议与累计确认(延时ack)。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"滑动窗口大小同通过tcp三次握手和对端协商，且受网络状况影响。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面是一个一个报文，实际可发一批报文，服务器并不是挨个去确认，上面回一个ack浪费资源，单独响应一个报文时，tcp本身一个报文至少20个字节再加上ip头报文20字节，所以一个ack至少40字节。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以延时ack的发送，如下图确认最后一个报文如5就可以，但这样也有一个问题如3的报文丢了，这时只能确认1和2连续报文，从3以后的报文全要重传，已确认的报文在缓冲区丢弃掉。 "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://s6.51cto.com/oss/202010/20/cf6792bf21872507abdce42c1d5e9ffc.png","title":null}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/e1/e1d94e25d65006fac26794493198094b.png","alt":"","title":"","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"作者：一角钱技术"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"来源：https://www.toutiao.com/i6885366707725009419/"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}