What is the difference between TCP and UDP? When would you use each?

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are both protocols used in the TCP/IP suite for communication over the internet. While they both provide transport layer services, there are significant differences between the two.

1. Connection-oriented vs Connectionless:
TCP is a connection-oriented protocol, which means it establishes a reliable and ordered connection between the sender and receiver before data transmission. It ensures that all packets are received in the correct order and retransmits any lost packets. On the other hand, UDP is a connectionless protocol, where data is sent without establishing a connection. It does not guarantee reliable delivery or packet ordering.

2. Reliability:
TCP provides reliable delivery of data by using acknowledgments and retransmissions. It ensures that all packets are received and in the correct order. UDP, being connectionless, does not provide reliability. It does not guarantee that all packets will be received or in the correct order.

3. Speed and Efficiency:
TCP has more overhead due to its reliability mechanisms, such as acknowledgment and retransmission. This additional overhead makes TCP slower compared to UDP. UDP, being lightweight and connectionless, is faster and more efficient. It is suitable for applications where speed is crucial, such as real-time streaming or online gaming.

4. Usage Scenarios:
TCP is commonly used for applications that require reliable and ordered data delivery, such as web browsing, email, file transfer, and database transactions. It is suitable for situations where data integrity and accuracy are essential. TCP is also used for applications that require flow control and congestion control.

UDP is used in scenarios where speed and efficiency are prioritized over reliability. It is commonly used for real-time applications like video streaming, voice over IP (VoIP), online gaming, DNS (Domain Name System), and SNMP (Simple Network Management Protocol). These applications can tolerate some packet loss or out-of-order delivery and can handle error recovery at the application level.

In summary, TCP is used when reliable and ordered data delivery is required, while UDP is used when speed and efficiency are prioritized, and some packet loss or out-of-order delivery can be tolerated. The choice between TCP and UDP depends on the specific requirements and characteristics of the application or service being used.