Understanding HTTP, TCP, UDP, and Socket Communication

HTTP, TCP, and UDP are fundamental communication protocols that define how data is exchanged between clients and servers.

TCP/IP is organized into four layers—network interface, network, transport, and application—with IP, ICMP, ARP, etc., in the network layer, and TCP/UDP in the transport layer.

HTTP is an application‑layer protocol used to transfer hypertext between web servers and browsers, operating over TCP.

A socket represents an endpoint for network communication; using sockets one can create TCP or UDP connections, enabling any protocol built on these transports.

The article explains the structure of HTTP requests (request line, headers, optional body) and responses (status line, headers, optional body), illustrating with a sample GET request captured by Fiddler.

Key HTTP request headers such as Accept, Referer, Accept‑Language, Content‑Type, Accept‑Encoding, User‑Agent, Connection, Content‑Length, Host, Pragma, Cookie, and Accept‑Charset are described, along with their purposes.

Response headers including Cache‑Control, Content‑Type, Expires, Last‑Modified, Server, X‑AspNet‑Version, X‑Powered‑By, Connection, Content‑Length, and Date are also detailed.

The differences between GET and POST methods are outlined, covering data placement, size limits, retrieval mechanisms, and security considerations.

GET http://www.cnblogs.com/ HTTP/1.1
Host: www.cnblogs.com