How does TCP ensure reliable transmission?

There are many factors in the network that may cause data to be lost, damaged or out of order during transmission, such as instability of the transmission medium, congestion, packet loss, etc. To address these problems, TCP introduces a series of mechanisms to ensure reliable data transmission.

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1 Connection Management Mechanism

TCP is a connection-oriented reliable transmission protocol. TCP uses three-way handshake and four-way handshake to establish and terminate the connection. Through the three-way handshake, the sender and receiver exchange information such as sequence number and window size to ensure that both parties are ready for data transmission. During the transmission process, the connection is terminated normally through four handshakes to ensure that the last data can be transmitted completely.

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2 Sequence Number and Confirmation Response Mechanism

TCP tracks the transmission of data by assigning a sequence number to each byte. The sender divides the data into multiple segments according to the sequence number and sends them to the network. The receiver informs the sender that the data has been successfully received through the confirmation (ACK) mechanism. If the sender does not receive the confirmation within a certain period of time, it will resend the corresponding data.

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3 Retransmission Mechanism

To ensure reliable data transmission, TCP starts a timer after sending data. If no confirmation response is received within the timer, the data is considered lost and the sender will resend the data (timeout retransmission). In addition, if multiple confirmations are received for the same data packet, it means that data is also lost, which will also trigger retransmission (fast retransmission).

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4 Flow Control

Flow control is a mechanism by which the receiver regulates the sender's sending speed so that it does not send too fast. The sliding window mechanism allows the sender to send multiple data segments before receiving a confirmation response, thereby improving transmission efficiency. The receiver uses the window size to inform the sender of the amount of data that can be received. The sender performs flow control based on the window size to ensure that it does not send data that exceeds the receiver's processing capacity.

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5 Congestion Control

TCP also uses congestion control mechanisms to optimize network performance and avoid network congestion. The congestion control algorithm adaptively adjusts the sender's sending rate according to the network congestion situation to prevent excessive data from being injected into the network, thus avoiding network congestion and data loss.

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TCP uses the above mechanisms to ensure reliable data transmission and ensure the integrity, consistency and correctness of data in the network. Whether dealing with network packet loss, disorder, congestion or other abnormal situations, TCP can adaptively adjust the transmission strategy and provide reliable transmission services.

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