Communication Protocols You Should Know

Protocols are the rules that let devices talk. They describe how data is formatted, how connections start, how errors are detected, and how messages arrive. Some rules focus on security, others on speed. Knowing a few basics helps you design apps, avoid common mistakes, and troubleshoot problems.

Core ideas

TCP is reliable and connection-oriented. It uses a handshake (SYN, SYN-ACK, ACK) to start a session. Data arrives in order and can be retried if it is lost. This reliability can add latency, but it helps most web and file traffic.

UDP is faster and connectionless. There is no built-in guarantee of delivery, order, or duplicate protection. Use UDP for real-time or streaming when speed matters more than perfect accuracy.

Common protocols by purpose

  • HTTP and HTTPS: HTTP is the language of the web. It is stateless and often plain text. HTTPS adds TLS to encrypt traffic, protecting privacy and integrity.

  • Email: SMTP handles sending; IMAP or POP3 retrieve messages. These work together to move mail across servers.

  • DNS: Translates domain names to IP addresses. It is fast, usually UDP, with, when needed, TCP for larger responses.

  • File transfer: FTP and SFTP. FTP is older and not encrypted by default; SFTP runs over SSH and is secure.

  • IoT and messaging: MQTT is a lightweight publish-subscribe protocol; CoAP is another option for small devices.

  • Real-time: WebSocket provides a persistent channel after an initial HTTP handshake, good for live data and chat.

  • Security basics: TLS (on top of TCP) encrypts traffic for many protocols, protecting data in transit.

Choosing a protocol for your task

  • Reliability needs: value delivery guarantees? TCP-based protocols (HTTP(S), MQTT with QoS) fit well.

  • Latency and bandwidth: UDP or WebSocket can reduce delays.

  • Security: encrypted channels with TLS are highly recommended.

  • Network constraints: some networks block certain ports; HTTP(S) on 443 is often easiest to reach.

Example: a browser loads a page via HTTPS. It performs a TLS handshake, then sends an HTTP GET. The server replies with HTML and assets.

Key Takeaways

  • Know the core transport options: TCP (reliable) vs UDP (fast).
  • Learn major application protocols: HTTP/HTTPS, SMTP, DNS, MQTT.
  • Always consider security and encryption with TLS.