TCP
Transmission Control Protocol — a connection-oriented Layer 4 protocol that guarantees reliable, ordered delivery.
TCP (Transmission Control Protocol) is a connection-oriented Layer 4 protocol that establishes a session via a three-way handshake before data transfer and tracks every segment to guarantee reliable, ordered delivery. It uses sequence and acknowledgment numbers to detect lost segments and retransmit them, plus flow-control mechanisms like windowing to prevent receiver overload. Common TCP-based services include HTTP (80), HTTPS (443), FTP (21), SSH (22), and SMTP (25). The key exam contrast is UDP: TCP adds reliability at the cost of latency and overhead, while UDP trades delivery guarantees for speed. DNS normally uses UDP but switches to TCP for zone transfers and large responses.
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