TCP/IP (Transmission Control Protocol/Internet Protocol) is the most fundamental protocol of the Internet, forming the basis of the global interconnected network. It consists of two main parts: the IP protocol at the network layer and the TCP protocol at the transport layer. These two protocols work together to ensure that data can be accurately transmitted from one location to another in a complex network environment.
Simple Explanation:
- TCP (Transmission Control Protocol): Responsible for detecting and handling issues that arise during transmission. Once a problem is detected, TCP sends a signal requesting the retransmission of data until all data arrives safely and correctly at its destination. TCP provides a reliable, connection-oriented service, ensuring transmission reliability and flow control through the “acknowledgment with retransmission” technique and the “sliding window” mechanism.
- IP (Internet Protocol): Assigns a unique address to each connected device to facilitate the routing of data packets across the network. The IP layer receives packets from lower layers (such as Ethernet device drivers) and forwards them to higher layers (such as TCP or UDP), and vice versa. However, IP itself does not guarantee the order or integrity of packets, making IP packets unreliable.
Workflow of IP and TCP
- Operation of the IP Layer:
- Receives packets from the network interface layer and forwards them to the TCP or UDP layer based on the destination address.
- Similarly, the IP layer is also responsible for passing packets from the TCP or UDP layer back to the network interface layer for physical transmission.
2. Operation of TCP:
- Establishes a connection using a three-way handshake and disconnects using a four-way handshake.
- Uses sequence numbers (seq) and acknowledgment numbers (ack) to ensure reliable data transmission.
- Utilizes the sliding window mechanism for flow control to prevent the sender from sending data too quickly for the receiver to process in time.
Three-Way Handshake and Four-Way Handshake of TCP Protocol
Three-Way Handshake (Connection Establishment):
- The client sends a SYN packet to the server to request synchronization.
- Upon receiving the SYN, the server responds with a SYN+ACK packet.
- The client receives the SYN+ACK and sends an ACK confirmation, establishing the connection.
Four-Way Handshake (Connection Termination):
- The client sends a FIN packet indicating no more data to send.
- Upon receiving the FIN, the server sends an ACK confirmation but may still be sending data.
- When the server finishes sending data, it sends a FIN packet to the client.
- The client receives the FIN and sends an ACK confirmation, entering the TIME_WAIT state, waiting for a period before closing the connection.
Why Do We Need Three-Way Handshake and Four-Way Handshake?
- Reason for Three-Way Handshake: To avoid duplicate connection requests caused by network delays or packet loss, which would waste server resources.
- Reason for Four-Way Handshake: To ensure both parties can completely stop data transmission, thoroughly releasing resources and avoiding unnecessary resource occupation.
Common Application Layer Protocols Using TCP
- FTP (File Transfer Protocol): Used for transferring files over the network.
- Telnet (Remote Login Protocol): Allows users to remotely log into another computer to execute commands.
- SMTP (Simple Mail Transfer Protocol): Used for sending emails.
- POP3 (Post Office Protocol version 3): Used for receiving emails.
- HTTP (Hypertext Transfer Protocol): Used for communication between web browsers and website servers.
Conclusion
The TCP/IP protocol suite is not only the core of Internet communication but also the foundation for building modern network applications. A deep understanding of how TCP/IP works, especially the three-way handshake and four-way handshake processes of TCP, helps network engineers better design, deploy, and maintain efficient and reliable network services. Whether developing new network applications or troubleshooting existing network environments, mastering this foundational knowledge is crucial.
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