Introduction to the TCP/IP Model

The TCP/IP model is a network protocol architecture that is the foundation of the Internet and is widely used in modern networks. The TCP/IP model consists of four layers, each responsible for different functions and tasks.
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Hierarchical structure of the TCP/IP model

Network Interface Layer (Network Interface Layer): The network interface layer is also called the physical interface layer, which is responsible for the physical connection and data transmission between different devices in the network. At this level, data is divided into frames and transmitted over physical media such as Ethernet, Wi-Fi, etc. This layer also handles hardware drivers and device address assignment (such as MAC addresses).
Internet Layer: The Internet layer is the core layer in the TCP/IP model, mainly responsible for the routing and forwarding of data packets. At this level, data packets are forwarded by routers according to the destination IP address, and the main protocol used is Internet Protocol (IP). Additionally, protocols such as the Internet Control Message Protocol (ICMP) are used for network troubleshooting and error reporting.
Transport Layer: The transport layer provides end-to-end reliable data transmission for applications. There are two main protocols that operate at this level: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). TCP provides reliable and connection-oriented communication, which ensures the reliable transmission of data through sequence number, confirmation response and retransmission mechanism. UDP is a connectionless protocol, which provides fast data transmission without establishing and maintaining connections.
Application Layer (Application Layer): The application layer is the layer that interacts most directly with users, including various applications and protocols. At this level, users communicate with the network using various applications such as web browsers, email, file transfer, etc. Common application layer protocols include Hypertext Transfer Protocol (HTTP), Simple Mail Transfer Protocol (SMTP), and File Transfer Protocol (FTP).

In summary, the TCP/IP model consists of four layers, including the network interface layer, the Internet layer, the transport layer, and the application layer. This model provides a framework for describing and organizing individual protocols and functions in the network. The design of the TCP/IP model enables different devices and applications to communicate with each other and provides the basis for the development of the Internet.

network interface layer

The network interface layer of TCP/IP is responsible for handling the details related to the transmission medium and providing a consistent network interface for the upper layer. Therefore, the network interface layer of the TCP/IP model roughly corresponds to the data link layer and physical layer of the OSI reference model, and usually includes interface drivers and network interface cards for computers and network devices.
Typical network interface layer technologies include common Ethernet, FDDI (Fiber Distributed Data Interface, Fiber Distributed Data Interface) and Token Ring (Token Ring) and other LAN technologies, and SLIP (SerialLine IP, Serial Line IP) for serial connections. Line IP), HDLC (High-level Data Link Control, advanced data link control) and PPP (Point-to-Point Protocol, point-to-point protocol) and other technologies.

network layer

The network layer is a key part of the TCP/IP system. Its main function is to enable hosts to send information to any network and deliver it to the correct destination host.
The network layer defines the packet format and its protocol - IP (Internet Protocol, Internet Protocol) .
The network layer uses IP address (IP address) to identify network nodes; uses routing protocols to generate routing information, and implements packet forwarding based on these routing information, so that packets can be accurately transmitted to the destination; uses ICMP (Internet ControlMessage Protocol, Internet control message protocols), IGMP and other protocols to help manage the network.
ICMP is also generally regarded as a network layer protocol. ICMP transmits relevant information of the IP protocol on the Internet through a set of predefined messages, thereby providing management and control functions for the IP network. A typical application of ICMP is to detect the availability of IP networks.

transport layer

The transport layer of TCP/IP is located between the application layer and the network layer, and is mainly responsible for providing end-to-end connections for applications on two hosts.
The transport layer protocol of TCP/IPDE includes TCP (Transmission Control Protocol, Transmission Control Protocol) and UDP (User Datagram Protocol, User Datagram Protocol).

The main role of the TCP/IP transport layer protocol

Provide connection-oriented or connectionless services: The transport layer protocol defines whether a reliable connection relationship needs to be established between the two ends of the communication. TCP is connection-oriented, while UDP is connectionless.
Maintain connection status: TCP establishes a connection relationship before communication, and the transport layer protocol must record this connection relationship in its database, and maintain the connection relationship through a certain mechanism, and discover connection failures in time.
Segmentation and encapsulation of application layer data: Application layer data is often a large block or continuous data stream, while the network can only send data packets of limited length, and the transport layer protocol must divide it into appropriate segments before transmitting application layer data. Size of the segment, and then sent to the IP protocol.
Realize multiplexing: An IP address can identify a host, but there may be multiple programs accessing the network on a host at the same time, so TCP/UDP uses port numbers (PortNumber) to identify these upper-layer applications, so that these programs Network channels can be reused.
Reliable data transmission: Errors, loss, out-of-sequence and other problems may occur in the process of data transmission across the network. The transport layer protocol must be able to detect and correct these problems.
- TCP checks errors in data transmission through mechanisms such as sequence numbers and checksums, and can retransmit erroneous data.
- UDP provides unreliable data transmission, and the reliability of data transmission is guaranteed by the application layer.
Execute flow control: Use flow control to prevent packet loss caused by network congestion. TCP controls end-to-end traffic through a sliding window mechanism.

application layer

The application layer directly deals with users and applications, and is responsible for providing interfaces to software so that programs can use network services. The network services here include file transfer, file management, e-mail message processing, and so on. Typical application layer protocols include Telnet, FTP, SMTP, SNMP, etc.

Telnet refers both to this application and to the protocol itself. Telnet provides users with a way to log in to a remote server through a networked terminal.

FTP (FileTransferProtocol, File Transfer Protocol) is an Internet standard for file transfer. FTP supports text files (such as ASCII, binary, etc.) and byte stream-oriented file structures.
- FTP uses the transport layer protocol TCP to perform file transfers between terminal systems that support FTP. Therefore, FTP is considered to provide reliable connection-oriented file transfer capabilities and is suitable for file transfers over long-distance and less reliable lines.

TFTP (TrivialFileTransferProtocol, Simple File Transfer Protocol)) is also used for file transfer, but TFTP uses UDP to provide services and is considered unreliable and connectionless. TFTP is typically used for reliable intra-LAN file transfers.

SMTP (SimpleMailTransferProtocol, Simple Mail Transfer Protocol) supports Internet transmission of text messages. All operating systems have client programs that use SMTP to send and receive e-mail, and most Internet service providers use SMTP as their outgoing mail service protocol.

SNMP (Simple Network Management Protocol, Simple Network Management Protocol) is responsible for monitoring and maintaining network devices, and supports security management and performance management.

HTTP (HypertextTransferProtocol, Hypertext Transfer Protocol) is the basis of WWW, and web pages on the Internet are mainly transmitted through HTTP.

The omnipotent TCP/IP model: the superhero of network communication

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