Difference between TCP and UDP

Parameter	TCP (Transmission Control Protocol)	UDP (User Datagram Protocol)
Connection	Connection-oriented (3-way handshake first)	Connectionless — no setup/teardown
Reliability	Reliable: ACKs, retransmission, sequencing	Unreliable: best-effort delivery
Ordering	Segments delivered in order using sequence numbers	No ordering guarantee
Error/flow control	Yes — checksum + retransmission, sliding-window flow control	Only a checksum; no retransmission, no flow control
Congestion control	Yes — slow start, congestion avoidance, fast recovery	None
Header overhead	20 bytes minimum (up to 60 B with options)	Fixed 8 bytes
Data unit	Segment (byte stream, no message boundaries)	Datagram (message-oriented, preserves boundaries)
Duplication	Duplicates detected and discarded	Possible duplicates passed to the app
Application	HTTP, SMTP, FTP control, file transfer, web, e-mail — where accuracy matters	DNS, DHCP, SNMP, streaming voice/video, VoIP, online games — where speed matters
Speed / latency	Slower due to handshakes and ACK overhead	Faster, low overhead
Broadcast/multicast	Not supported	Supported
Termination	Graceful connection release (FIN)	No termination concept

In brief: TCP trades speed for guaranteed, ordered, error-free delivery over a virtual connection; UDP is lightweight and fast, delivering datagrams with no guarantees — chosen when timeliness matters more than perfect accuracy (or when the application implements its own reliability).