TCP, UDP, and the Three-Way Handshake
Tags: hacking, certification
Published: 2023-07-14 06:47:57

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are both transport layer protocols used in computer networks to enable communication between devices. They have different characteristics and are suitable for different types of network applications.

TCP is a connection-oriented protocol that provides reliable and ordered delivery of data packets. It establishes a virtual circuit between the sender and receiver and ensures that data is received without errors and in the correct order. TCP achieves reliability through various mechanisms, such as acknowledgments, retransmissions, and flow control. It is commonly used for applications that require error-free and ordered delivery, such as web browsing, email, and file transfer.

On the other hand, UDP is a connectionless protocol that offers a lightweight and low-latency communication mechanism. Unlike TCP, UDP does not establish a dedicated connection before transmitting data. It simply encapsulates data into packets and sends them to the destination without any guarantee of delivery or order. UDP is useful for real-time applications where low latency is critical, such as streaming media, online gaming, and DNS (Domain Name System) lookups.

The Three-Way Handshake, also known as the TCP handshake, is a process that TCP uses to establish a connection between two devices. It is essential for initiating a reliable and ordered data transfer. The handshake involves three steps:

1. SYN (Synchronize): The client sends a TCP packet with the SYN flag set to the server. This packet contains a random sequence number and other TCP control information. The client enters the SYN_SENT state, waiting for a response.
2. SYN-ACK (Synchronize-Acknowledgment): If the server is willing to establish a connection, it responds with a TCP packet that has the SYN and ACK (acknowledgment) flags set. The packet includes its own random sequence number and an acknowledgment number that confirms the receipt of the client's SYN packet. The server enters the SYN-RECEIVED state.
3. ACK (Acknowledgment): Finally, the client acknowledges the server's response by sending a TCP packet with the ACK flag set. This packet contains the server's sequence number incremented by one and an acknowledgment number confirming the server's receipt. The client enters the ESTABLISHED state, and the server transitions to the ESTABLISHED state upon receiving this acknowledgment.

At this point, the TCP connection is established, and both the client and server can start exchanging data packets. If any of the steps fail or time out, the connection establishment fails, and the handshake is retried.

The Three-Way Handshake ensures that both devices agree on initial sequence numbers, confirms each other's readiness to establish a connection, and synchronizes the initial sequence number and acknowledgment number. This process provides a reliable foundation for the subsequent data transfer, error recovery, and flow control mechanisms employed by TCP.

In summary, TCP and UDP are transport layer protocols with different characteristics suited for different network applications. TCP offers reliable and ordered delivery, while UDP provides lightweight and low-latency communication. The Three-Way Handshake is a crucial process used by TCP to establish a connection between devices, ensuring synchronization and reliability in data transmission.