TCP (Transmission Control Protocol) starts with a process called the TCP handshake. This handshake initializes and negotiates parameters between two devices (typically a client and a server) before data transmission begins. The TCP handshake involves three steps: SYN, SYN-ACK, and ACK. First, the client sends a SYN (synchronize) packet to the server to initiate a connection request. The server responds with a SYN-ACK (synchronize-acknowledgment) packet, indicating it received the SYN and is willing to establish a connection. Finally, the client sends an ACK (acknowledgment) packet back to the server, confirming receipt of the SYN-ACK. Once this handshake is complete, both sides have agreed on initial sequence numbers, window sizes, and other parameters necessary for reliable data transmission.
TCP is formed by encapsulating data into segments for transmission across a network. When an application sends data, TCP breaks it into smaller units known as segments. Each segment includes a TCP header containing control information such as sequence numbers, acknowledgment numbers, window sizes, and checksums for error detection. These segments are then passed to the IP layer for routing and delivery across the network. Upon receipt, TCP on the receiving end reassembles the segments into the original data stream, ensuring reliable and ordered delivery of data even if packets arrive out of order or are lost.
The three fundamental steps of TCP are:
- Connection Establishment: This involves the TCP handshake process described earlier, where a client and server exchange SYN, SYN-ACK, and ACK packets to establish a reliable connection before data transmission begins.
- Data Transfer: Once a connection is established, TCP manages the transmission of data in segments. Data segments are sent from the sender to the receiver, and TCP ensures that they arrive in the correct order and without errors using sequence numbers for ordering and acknowledgments for reliability.
- Connection Termination: When data transfer is complete, TCP initiates a connection termination process to gracefully close the connection. This involves a handshake where both sides exchange FIN (finish) packets to close the connection in a coordinated manner. Once both parties acknowledge the FIN packets, the connection is fully closed, and resources allocated to the connection are released.
TCP works by establishing a connection-oriented communication channel between two hosts over a network. It ensures reliable delivery of data through mechanisms such as sequence numbers, acknowledgments, and flow control. When a sender transmits data, TCP breaks it into segments, adds headers with control information, and sends them to the recipient. The recipient acknowledges receipt of each segment and requests retransmission of any lost or corrupted segments. TCP also manages flow control to prevent overwhelming the receiver with data, adjusting transmission rates based on network conditions. This combination of features allows TCP to provide error-free, ordered, and reliable data transfer across diverse networks, making it suitable for applications that require guaranteed delivery and precise control over data transmission.