TCP vs UDP

The two most important protocols at the Transport Layer are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol), and they serve very different purposes. TCP is connection-oriented. This means before any data transfer begins, a connection must be established between the sender and receiver through a three-way handshake. TCP is designed for reliability. It guarantees that all data sent will be received in the correct order and without errors. It achieves this using sequence numbers to track packets, acknowledgments (ACKs) to confirm receipt, and retransmissions for lost or corrupted packets. TCP also implements flow control, ensuring the sender doesn't send data faster than the receiver can process it, and congestion control, which throttles the sending rate when the network is congested. This reliability comes at the cost of higher overhead and latency. Because of this, TCP is used for applications like HTTP (web), FTP (file transfer), and SMTP (email), where data integrity is crucial. On the other hand, UDP is connectionless. It sends messages, called datagrams, without establishing a connection first. It's a 'fire-and-forget' protocol. UDP provides no guarantees of delivery, ordering, or error checking (though it has an optional checksum). Its main advantages are simplicity, low overhead, and speed. This makes UDP ideal for applications where speed is more important than perfect reliability, such as DNS lookups, DHCP, real-time video and audio streaming, and online gaming.