What are the differences between TCP and UDP?

TCP (Transmission Control Protocol)

TCP is a connection-oriented protocol that requires establishing a connection (three-way handshake) before transmission, ensuring reliable and ordered data delivery.

Characteristics:

• Connection establishment: Three-way handshake (SYN → SYN-ACK → ACK)
• Connection termination: Four-way handshake
• Reliable transmission: Ordered, no duplicates, no loss (ACK confirmation and retransmission)
• Flow control and congestion control
• Slower but stable

UDP (User Datagram Protocol)

UDP is a connectionless protocol that sends data directly without guaranteeing reliability.

Characteristics:

• Connectionless, sends directly
• No guarantee of order or delivery
• No retransmission mechanism
• Fast with low latency
• Supports broadcast and multicast

Key Comparison

Feature	TCP	UDP
Connection	Connection-oriented	Connectionless
Reliability	High (ACK/retransmit)	Low (no guarantee)
Order	Guaranteed	Not guaranteed
Speed	Slower	Faster
Use Cases	HTTP, FTP, Email	Live streaming, Gaming, DNS, VoIP

When to Use

• TCP: When reliable transmission is required — web browsing (HTTP/HTTPS), file transfer (FTP), email
• UDP: When low latency is more important than reliability — video streaming, online gaming, DNS queries