TCP
NetworkingTCP is a core Internet transport protocol that delivers data reliably between applications using ordered, error-checked streams. It establishes a connection, breaks content into segments, confirms delivery with acknowledgments, retransmits lost data, and controls flow and congestion to avoid overwhelming networks or endpoints. Most web traffic, including HTTP/1.1 and many HTTPS connections, depends on TCP for consistent delivery.
How It Works
TCP (Transmission Control Protocol) sits above IP and provides a connection-oriented channel between two endpoints identified by IP addresses and ports. A TCP session typically begins with a three-way handshake (SYN, SYN-ACK, ACK) to agree on initial sequence numbers and confirm both sides are reachable. Data is then sent as numbered segments so the receiver can reassemble bytes in order, even if packets arrive out of sequence.
Reliability comes from acknowledgments and retransmissions: the receiver confirms which bytes arrived, and the sender resends missing segments after a timeout or duplicate acknowledgments. TCP also includes flow control (the receive window) to prevent a fast sender from overrunning a slow receiver, and congestion control to reduce sending rates when the network shows signs of congestion. These mechanisms improve correctness and stability, but they add overhead and latency compared with connectionless protocols like UDP.
Why It Matters for Web Hosting
TCP behavior directly affects perceived site speed and reliability because it governs connection setup, retransmissions, and throughput. When comparing hosting plans, TCP performance is influenced by server CPU, network interface capacity, kernel tuning, and the quality of the host network and upstream routing. Features like HTTP/2 over TCP, TLS termination, load balancers, and firewalls all interact with TCP, so understanding it helps you evaluate limits on concurrent connections, bandwidth, and latency-sensitive workloads.
Common Use Cases
- Serving web pages and APIs over HTTP/1.1 and HTTP/2 (typically HTTPS over TCP)
- Secure remote administration via SSH (TCP port 22)
- Email transport and access protocols such as SMTP, IMAP, and POP3
- Database connections between application servers and database servers (for example, PostgreSQL or MySQL)
- File transfer and synchronization tools that require reliable delivery (for example, SFTP over SSH)
TCP vs UDP
TCP prioritizes reliability and ordered delivery, making it a good fit for web pages, logins, and database queries where missing or duplicated data is unacceptable. UDP is connectionless and does not guarantee delivery or ordering, but it can reduce latency and overhead for real-time traffic. In hosting, UDP is common for DNS queries, some monitoring, and modern protocols like QUIC (used by HTTP/3), while TCP remains the default for many traditional web and application services.