Network Basics: TCP/IP protocol responsibilities and three common models

1. The main responsibilities of TCP/IP protocol

● Break down the messages to be communicated into manageable data chunks that can be efficiently moved through the transmission medium.

● Implement connection with network adapter hardware (MAC address).

● The addressing function ensures that the sending computer can accurately find the receiving computer, and the receiving computer can identify and receive the specified data.

● Efficiently route data to the subnet where the destination computer is located, even if the source subnet and destination subnet are on different physical networks.

● Perform error control, flow control, and acknowledgment: For reliable communication, the sending and receiving computers must be able to detect and correct transmission errors and properly control the flow of data.

● Implement the function of receiving data from local applications and transmitting it to external networks.

● Receive data from external networks and transmit it to local applications.

2. Three common models of TCP/IP networks

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2.1 Common four-layer model

The four-layer model is our most common model, including network access layer, internet layer, transport layer, and application layer. The four-layer model is as follows from low to high:

2.1.1 Network Access Layer

The network access layer is the lowest layer of the four-layer model and is mainly responsible for the physical transmission of data. It involves hardware devices such as network cards, hubs, and switches to transmit data from the sender to the receiver through physical media (such as Ethernet cables). During the transmission process, the data is converted into a bit stream and transmitted through the physical network. The network access layer also handles the encapsulation and decapsulation of data to ensure the correct transmission of data on the physical medium. The MAC address is used to uniquely identify and locate devices in the network, thereby achieving accurate data transmission.

2.1.2 Internet Layer

The Internet layer is mainly responsible for routing and forwarding data packets between networks, ensuring that data packets can reach their destination across different physical networks. It uses IP addresses to identify communication devices in the network and determines the most ideal transmission path for data packets through routing protocols. The Internet layer needs to handle the fragmentation and reassembly of data packets to adapt to the transmission requirements of different networks, and provide error detection and correction mechanisms for the network layer.

2.1.3 Transport Layer

The transport layer provides end-to-end reliable transmission services to ensure data integrity and sequence. It uses port numbers to identify applications and services. There are two transmission protocols: TCP and UDP. TCP provides reliable, connection-oriented services to ensure data integrity and sequence, and is suitable for applications that require high data reliability. UDP provides unreliable, connectionless services, and is suitable for applications that require high real-time performance, such as video conferencing and live broadcasting.

2.1.4 Application Layer

The application layer is the highest layer of the four-layer model and directly provides services for user applications. It provides applications for network troubleshooting, file transfer, remote control, and Internet operations, and also supports application programming interfaces (APIs), allowing programs written for specific operating systems to directly access the network.

2.2 Five-layer model

The main difference between the five-layer model and the four-layer model is that the network layer of the four-layer model is replaced by the physical layer and the data link layer. The five-layer model is as follows from low to high:

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2.2.1 Physical layer

The physical layer is the infrastructure layer of network communication, involving various transmission media such as networks and optical fibers. It provides basic physical connections for the upper layers, enabling data to be actually transmitted between different devices.

2.2.2 Data Link Layer

The data link layer handles the transmission of data frames between devices, focusing on communication between adjacent nodes. For example, it is responsible for data transmission between switches and network cards connected by network cables, optical fibers, or network interfaces. This layer ensures reliable delivery of data in a local network.

2.2.3 Network Layer

The network layer is mainly responsible for address management and routing forwarding. It records the IP addresses of the source host and the destination host and selects an efficient and reliable path to transmit data. The focus of this layer is path planning to ensure that data can find the best transmission route in a complex network environment.

2.2.4 Transport Layer

The transport layer is responsible for managing the data transmission between two nodes and ensuring the reliable delivery of data. It does not care about the transmission path of data in the intermediate nodes, but focuses on the communication between the starting point and the end point, and takes measures to ensure that the data can be delivered to the target address accurately.

2.2.5 Application Layer

The application layer focuses on processing the data received from the transport layer. During software development, developers can use specific programming techniques (Java, C#, C++, etc.) to read and write data from the transport layer. The main responsibility of the application layer is to process this data according to the predetermined format without involving the specific implementation details of the transport layer.

2.3 The early three-tier model of ARPAnet described in RFC871

In November 1969, the Advanced Research Projects Administration (ARPA) of the U.S. Department of Defense began to build a network named ARPAnet, which was the predecessor of the Internet and a network for military purposes.

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This model has a profound impact on network architecture, and many modern network architectures refer to this model to a greater or lesser extent. The three-layer model is as follows from low to high:

2.3.1 Network Layer

The network layer is primarily responsible for providing basic packet exchange functions between communicating entities.

2.3.2 Network Access Layer

The network access layer provides network interconnection hardware and software, allowing different network devices to be interconnected.

2.3.3 Host Layer

Equivalent to the user layer, the user's terminal device is directly connected to other hosts.

Conclusion

The above is an introduction to the main responsibilities of TCP/IP and the three network models. I hope it will help you understand the TCP/IP protocol!