The first step in learning networking: a comprehensive analysis of the OSI and TCP/IP models

Hello, everyone! I am your good friend Xiaomi. Today we are going to talk about the heavyweights in the basic knowledge of the network - the OSI model and the TCP/IP model! The world of the network is like a huge maze, and these two models are like maps prepared for us to help us sort out the complex process of network communication. Are you ready? Let's start this wonderful network journey together!

OSI seven-layer model

The OSI (Open Systems Interconnection) model is a network architecture model proposed by the International Organization for Standardization (ISO). It divides the network communication process into seven layers, and each layer is responsible for a specific network function. Let's take a look at what these network layers do layer by layer!

1. Physical Layer

• Function: The physical layer is the first layer of the OSI model and is mainly responsible for transmitting raw bit streams. It defines the standards of physical devices, such as cable type, signal voltage, transmission speed, etc.
• Example: You can think of the physical layer as our network wires, optical fibers, cables, and even radio waves. They are the infrastructure that our data travels on.

2. Data Link Layer

• Function: The data link layer is responsible for reliable data transmission between nodes. Its main function is to encapsulate, address, detect and correct errors of the original data bit stream transmitted from the physical layer.
• Example: The classic representative of the data link layer is the MAC address (Media Access Control Address) that we often talk about, as well as the Ethernet protocol.

3. Network Layer

• Function: The network layer is responsible for the transmission and routing of data packets in the network. It determines the best path for data to go from source to destination.
• Example: IP address (Internet Protocol Address) is a product of the network layer. Routers work at this layer to help data find the fastest transmission route.

4. Transport Layer

• Function: The transport layer ensures reliable transmission and correct order of data, provides error recovery and flow control mechanisms. It creates an end-to-end connection when sending and receiving data.
• Example: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are representative protocols of the transport layer.

5. Session Layer

• Function: The session layer is responsible for establishing, managing, and terminating sessions between applications. It handles the organization and synchronization of conversations and manages the order of data exchange.
• Example: In video conferencing software, the session layer is responsible for managing and maintaining your connection with other participants.

6. Presentation Layer

• Function: The presentation layer is responsible for formatting and translating data, including data encryption, decryption, compression, and decompression.
• Example: When you browse the web, the encryption and decryption process of the HTTPS protocol is handled at this layer.

7. Application Layer

• Function: The application layer is the direct interface for users to interact with the network, and provides interfaces for network services, such as file transfer, email, and remote login.
• For example: FTP (File Transfer Protocol) and HTTP (HyperText Transfer Protocol) that we use in daily life are both application layer protocols.

TCP/IP five-layer model

The TCP/IP model is another widely used network model that simplifies the OSI model and divides it into five layers. Although the number of layers has been reduced, the functions have not changed! Let's take a look at what this model is all about.

1. Physical Layer

• Function: Like the OSI model, the physical layer of the TCP/IP model is responsible for transmitting the raw data bit stream. This layer defines the electrical characteristics of the physical devices and the transmission medium.
• Examples: Network cables, optical fibers, electrical cables, and radio waves also belong to this layer.

2. Data Link Layer

• Function: The data link layer is still responsible for reliable data transmission between nodes in the TCP/IP model, including data frame encapsulation, addressing, and error detection and correction.
• Examples: MAC addresses and Ethernet protocols are still typical representatives of this layer.

3. Network Layer

• Function: The network layer of the TCP/IP model is responsible for the transmission and routing of data packets in the network, which has the same function as the network layer in the OSI model.
• Example: IP addresses and routers work at this layer to ensure that data packets reach their destination smoothly.

4. Transport Layer

• Function: The transport layer is also responsible for the reliable transmission and correct order of data in the TCP/IP model. It ensures data integrity through end-to-end connections.
• Example: TCP and UDP protocols function at this layer, providing reliable and unreliable data transmission services respectively.

5. Application Layer

• Function: The TCP/IP model combines the session layer, presentation layer, and application layer of the OSI model into an application layer. This layer interacts directly with users and provides network services.
• Example: HTTP, FTP, SMTP (Simple Mail Transfer Protocol) and other protocols are all application layer protocols.

Comparison between OSI and TCP/IP models

Now that we understand the layers of both models, let’s compare them:

• Layer structure: OSI model has seven layers, while TCP/IP model has five layers. TCP/IP model combines session layer, presentation layer, and application layer into one application layer.
• Flexibility: The OSI model is a theoretical model that is highly abstract and flexible. The TCP/IP model is more practical because it is directly based on the Internet protocol stack.
• Functional division: The functional division of each layer in the OSI model is relatively detailed, while the TCP/IP model is more simplified and focuses on implementation in practical applications.
• Protocol standards: Each layer in the OSI model has different protocols, while the TCP/IP model mainly focuses on the core protocols (such as IP and TCP) at the network layer and transport layer.

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Through this article, I believe everyone has a deeper understanding of the OSI seven-layer model and the TCP/IP five-layer model. These two models not only help us sort out the complex process of network communication, but also provide us with a theoretical basis for designing and maintaining the network.