# TCP 3-Way Handshake Process The TCP 3-Way Handshake is a process used by the Transmission Control Protocol (TCP) to establish a reliable connection between a client and a server before data transfer. It ensures that both sides are synchronized and ready to communicate. --- ## Problems TCP is designed to solve Without TCP, applications would need to handle these problems themselves: * Packet loss. * Out-of-order delivery. * Data Corruption. * Network Congestion * Flow control. --- ## **TCP 3-way Handshake Process** Communication over the internet follows the TCP/IP model. Applications like web browsers use the Application Layer, and their data is passed to the Transport Layer, where TCP and UDP work. * TCP is widely used because it provides reliable communication. * UDP is faster but unreliable (e.g., used in DNS lookups). ![TCP 3 Way Handshaking](https://media.geeksforgeeks.org/wp-content/uploads/handshake-1.png align="center") * **Step 1 (SYN):** In the first step, the client wants to establish a connection with a server, so it sends a segment with SYN(Synchronize Sequence Number) which informs the server that the client is likely to start communication and with what sequence number it starts segments with * **Step 2 (SYN + ACK):** Server responds to the client request with SYN-ACK signal bits set. Acknowledgement(ACK) signifies the response of the segment it received and SYN signifies with what sequence number it is likely to start the segments with * **Step 3 (ACK):** In the final part client acknowledges the response of the server and they both establish a reliable connection with which they will start the actual data transfer. --- ## How data transfer works in TCP ### **Segmenting** * When an application sends data (like an email or file), TCP breaks the data into smaller chunks called segments. * Each segment has a header containing information like sequence numbers, ports, and flags. * This makes it easier to send large amounts of data over the network reliably. ### **Routing via IP** * Once TCP creates segments, they are handed to IP (Internet Protocol). * IP is responsible for delivering the segments from the sender to the receiver, possibly through multiple routers. * TCP doesn’t care about the path—IP handles routing and addressing. ### **Reassembly at Receiver** * Segments may arrive out of order because they can take different paths through the network. * TCP at the receiver uses sequence numbers to reassemble the segments into the correct order to reconstruct the original message. ### **Retransmission** * If the sender does not receive an acknowledgment within a certain time, it resends the missing segment. * This ensures no data is lost, making TCP reliable. and lot more.. --- ## How TCP Ensures Reliability, Order, and Correctness * Retransmission TCP **retransmits** the missing segment if an ACK is not received in time * Order (Sequence Numbers) Every byte has a sequence number. Receiver get Buffers out-of-order segments and reassembles data correctly. --- ## How a TCP Connection Is Closed TCP connection termination is the process of closing an established TCP connection between two devices in an orderly way. It uses a four-step handshake (FIN-ACK exchange) to ensure that both sides have finished sending and receiving all data before the connection is fully closed. ## **Types of TCP Connection Release** TCP supports two types of connection releases like most connection-oriented transport protocols:  1. **Abrupt connection release:** In an Abrupt connection release, either one TCP entity is forced to close the connection or one user closes both directions of data transfer. 2. **Graceful connection release:** In the Graceful connection release, the connection is open until both parties have closed their sides of the connection. --- TCP is the protocol that turns an unreliable network into a reliable communication channel by using connections, acknowledgments, retransmissions, and flow control.