TCP (Transmission Control Protocol) works by establishing a reliable and ordered communication channel between two devices over a network. It operates at the transport layer of the TCP/IP protocol suite and ensures that data transmitted between sender and receiver arrives intact and in the correct sequence. TCP achieves this reliability through mechanisms such as sequence numbers, acknowledgments, checksums, and flow control. When a sender transmits data, TCP breaks it into segments, adds headers containing control information, and sends them to the receiver. The receiver acknowledges receipt of each segment and requests retransmission of any lost or corrupted segments, ensuring error-free data delivery.
TCP works step by step in several stages:
- Connection Establishment: The process begins with a TCP handshake, where the client and server exchange synchronization (SYN) packets to negotiate parameters and agree on initial sequence numbers. The steps include sending a SYN packet, receiving a SYN-ACK packet in response, and sending an ACK packet to confirm the connection.
- Data Transfer: Once the connection is established, data transmission occurs in segments. The sender breaks data into manageable chunks, adds TCP headers with sequence numbers, and sends them across the network. The receiver acknowledges each segment, allowing the sender to retransmit any lost segments.
- Flow Control: TCP implements flow control to manage data transmission rates based on receiver capacity. The receiver advertises a window size indicating how much data it can accept, preventing overload and ensuring efficient data transfer.
- Error Handling: TCP detects errors using checksums in segment headers. If errors are detected, the receiver discards the segment and requests retransmission using selective repeat or similar mechanisms.
- Connection Termination: When data exchange completes, TCP initiates a connection termination process. This involves exchanging FIN (finish) packets to gracefully close the connection, freeing up resources and ensuring both sides acknowledge the closure.
A TCP session refers to the entire lifecycle of a TCP connection between two hosts. It starts with the TCP handshake to establish a connection, includes data exchange using segments, manages flow control and error handling, and concludes with connection termination. Throughout the session, TCP manages state information, sequence numbers, acknowledgments, and other parameters to ensure reliable and orderly data transfer between sender and receiver.
TCP follows a layered approach in the TCP/IP model, where it operates at the transport layer. This model separates network communication into layers, with TCP handling end-to-end communication reliability and flow control. Below the transport layer, IP (Internet Protocol) manages addressing and routing, while above it, application layer protocols like HTTP, FTP, and SMTP use TCP services for reliable data exchange.
TCP data transfer begins with the sender breaking data into segments and adding TCP headers with sequence numbers. These segments are transmitted over the network to the receiver, which acknowledges receipt of each segment. If segments are lost or corrupted, the sender retransmits them based on receiver acknowledgments and selective repeat mechanisms. TCP ensures ordered delivery by numbering segments and reassembling them into the correct order at the receiver. This reliable data transfer mechanism allows TCP to provide error-free communication over unreliable network connections, making it suitable for applications requiring guaranteed delivery and precise data sequencing.