Network Knowledge &http Protocol

Protocols common to each layer in a network seven-tier model:

Common HTTP protocols work in the application layer

The working layer of the HTTP protocol:
The HTTP protocol is usually hosted on top of the TCP protocol, sometimes hosted on the TLS or SSL protocol layer, which is what we often call HTTPS. See:

Workflow for HTTP protocol:
An HTTP operation is called a transaction, and its working process can be divided into four steps:

1) First the client and the server need to establish a connection. As soon as you click on a hyperlink, the HTTP work begins.

2) After the connection is established, the client sends a request to the server in the form of a Uniform Resource Identifier (URL), protocol version number, followed by MIME information including the request modifier, client information, and possible content.

3) When the server receives the request, it gives the corresponding response information in the form of a status line, including the protocol version number of the information, a successful or incorrect code, followed by MIME information including server information, entity information, and possible content.

4) The information returned by the client receiving server is displayed on the user's display by the browser, and then the client disconnects from the server.

If an error occurs in one of the steps above, the information that generates the error is returned to the client, with the display output. For the user, these processes are done by HTTP itself, the user just click with the mouse, waiting for information to display it.

Tcp / ip
TCP is responsible for the communication between the application software (such as your browser) and the network software. IP is responsible for communication between computers. TCP is responsible for splitting the data and loading the IP packets, the IP is responsible for sending the packet to the recipient, the transfer process through the IP router is responsible for the traffic, network errors or other parameters to properly address, and then when they arrive to regroup them.

An HTTP operation is detailed throughout the process:

 1 ) 、地址解析， 如用客户端浏览器请求这个页面：http://localhost.com:8080/index.htm 从中分解出协议名、主机名、端口、对象路径等部分，对于我们的这个地址，解析得到的结果如下： 协议名：http 主机名：localhost.com 端口：8080 对象路径：/index.htm  在这一步，需要域名系统DNS解析域名localhost.com,得主机的IP地址。2）、封装HTTP请求数据包 把以上部分结合本机自己的信息，封装成一个HTTP请求数据包 3）封装成TCP包，建立TCP连接（TCP的三次握手）   在HTTP工作开始之前，客户机（Web浏览器）首先要通过网络与服务器建立连接，该连接是通过TCP来完成的，该协议与IP协议共同构建Internet，即著名的TCP/IP协议族，因此Internet又被称作是TCP/IP网络。HTTP是比TCP更高层次的应用层协议，根据规则，只有低层协议建立之后才能，才能进行更层协议的连接，因此，首先要建立TCP连接，一般TCP连接的端口号是80。这里是8080端口 4）客户机发送请求命令   建立连接后，客户机发送一个请求给服务器，请求方式的格式为：统一资源标识符（URL）、协议版本号，后边是MIME信息包括请求修饰符、客户机信息和可内容。 5）服务器响应 服务器接到请求后，给予相应的响应信息，其格式为一个状态行，包括信息的协议版本号、一个成功或错误的代码，后边是MIME信息包括服务器信息、实体信息和可能的内容。    实体消息是服务器向浏览器发送头信息后，它会发送一个空白行来表示头信息的发送到此为结束，接着，它就以Content-Type应答头信息所描述的格式发送用户所请求的实际数据 6）服务器关闭TCP连接 一般情况下，一旦Web服务器向浏览器发送了请求数据，它就要关闭TCP连接，然后如果浏览器或者服务器在其头信息加入了这行代码Connection:keep-alive

The TCP connection remains open after it is sent, so the browser can continue to send requests through the same connection. Maintaining a connection saves the time it takes to establish a new connection for each request and also saves network bandwidth.

Network Knowledge &http Protocol