Glossary

TCP and UDP

TCP and UDP are the two transport protocols of the internet. TCP guarantees delivery and order of packets at the cost of overhead. UDP is faster but "fire and forget" — no guarantees.

TCP (Transmission Control Protocol)

Connection-oriented: three-way handshake (SYN → SYN-ACK → ACK)
Guaranteed delivery: lost packets are retransmitted
Ordering: data arrives in the correct sequence
Flow control and congestion control
Uses: HTTP/HTTPS, SSH, email, databases

UDP (User Datagram Protocol)

No connection setup, no acknowledgements
Lower latency — no TCP overhead
Packets can be lost and arrive out of order
Uses: video streaming, VoIP, DNS, online games, HTTP/3 (QUIC over UDP)