Front-end 100 Questions: The Seven-layer Network Model and the Evolution of HTTP

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1. Network Architecture

There are many classification standards for network architecture: OSI architecture, TCP/IP architecture, and five-layer protocol architecture. OSI architecture is the most detailed architecture. The other TCP/IP architecture and five-layer protocol architecture are obtained by aggregating some layers of OSI architecture. The classification of the above three structures is as follows:

The TCP/IP architecture and the five-layer protocol architecture are both obtained by aggregating certain levels on the basis of the OSI architecture. So let's focus on the functions of each layer in the OSI architecture.

Physical Layer

The physical layer is the first layer. Its main function is to use the transmission medium to provide a physical connection for the data link layer to achieve transparent transmission of the bit stream, so that the bits in the frame can move from one node to the next. (Transmission of raw bit streams on mechanical, electronic, and timing interface communication channels)

Data Link Layer

The data link layer is mainly responsible for establishing and managing links between nodes. The task of this layer is to move the entire frame from one network element to an adjacent network element. (Physical addressing and converting the original bit stream into a logical transmission line)

Network Layer

The network layer is responsible for moving network layer packets called datagrams from one host to another. This layer includes the well-known Internet Protocol IP, which defines the various fields in the datagram and how end systems and routers act on these fields. (Controls the operation of the subnet, such as logical addressing, packet transmission, and routing)

Transport Layer

The main task of the transport layer is to provide general data transmission services for the communication between two host processes, mainly using TCP and UDP protocols. (Receive data from the session layer, split the data when necessary, and hand it over to the network layer, and ensure that these data segments reach the other end effectively)

Session Layer

The session layer is the interface between the user application and the network. Its main task is to provide the presentation layer of the two entities with methods for establishing and using connections. (Establishing and managing sessions between users on different machines)

Presentation Layer

The presentation layer interprets the commands and data from the application layer, assigns corresponding meanings to various codes, and transmits them to the session layer in a certain format. Its main function is to handle the representation of user information, such as encoding, data format conversion, encryption and decryption, etc. (The syntax and semantics of information and their associations, such as encryption and decryption, conversion and translation, compression and decompression)

Application Layer

The application layer is the interface between various applications and the network. Its function is to directly provide services to users and complete various tasks that users want to complete on the network. Common protocols include HTTP, HTTPS, FTP, SSH, etc. (Various application protocols, such as HTTP, FTP, SMTP, POP3)

Note: You can view the network protocol map published by Colasoft (http://www.colasoft.com.cn/download/network-protocol-map-2020.pdf)

2. HTTP0.9 - HTTP3.0 evolution

The HTTP protocol is constantly evolving and can be roughly divided into five versions: HTTP/0.9, HTTP/1.0, HTTP/1.1, HTTP/2.0, and HTTP3.0. Let's take a look at these versions.

2.1 HTTP/0.9

2.2 HTTP/1.0

2.3 HTTP/1.1

2.4 HTTP/2.0

2.5 HTTP/3.0

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