Master Computer Network Fundamentals: TCP/UDP, HTTP, Socket & More

Preface

Computer network fundamentals are essential for R&D and operations engineers but are often overlooked. This guide provides a clear, detailed overview of TCP/UDP, HTTP, Socket, and related concepts.

1. Computer Network Architecture

1.1 Overview

Definition: the set of layers and protocols in a computer network.

Purpose: defines the capabilities of the network.

1.2 Structure

The three main models are OSI, TCP/IP, and the five‑layer model.

OSI: conceptually clear but complex and rarely used in practice.

TCP/IP: core Internet protocol suite, widely applied in LAN and WAN.

Five‑layer: combines OSI and TCP/IP for teaching purposes.

Lower three layers form the communication sub‑network (data transport); upper three layers form the resource sub‑network (data processing); the transport layer connects them.

2. TCP Protocol

Transmission Control Protocol (TCP) is a transport‑layer communication protocol.

It belongs to the transport layer.

Application‑layer protocols based on TCP include HTTP, SMTP, FTP, Telnet, and POP3.

Additional TCP topics include three‑way handshake, four‑way termination, and error‑control mechanisms.

3. UDP Protocol

3.1 Definition

User Datagram Protocol (UDP) is a transport‑layer protocol.

3.2 Characteristics

Connection‑less, unreliable, message‑oriented, without congestion control.

3.3 Advantages & Disadvantages

Advantage: high speed.

Disadvantage: prone to packet loss, especially on poor networks.

3.4 Typical Applications

Scenarios requiring high communication speed, e.g., DNS, FTP, SNMP, NFS.

3.5 UDP Header Format

UDP datagram consists of a data field and an 8‑byte header with four fields.

4. HTTP Protocol

Brief introduction to HTTP.

5. Socket

5.1 Overview

A socket is an abstraction layer between the application layer and the TCP/IP protocol suite, providing a programming interface (API).

Socket is not a protocol; it is an API in the transport layer that enables communication over TCP/IP, including on Android platforms.

Socket pair example: Socket = {(IP1:PORT1), (IP2:PORT2)} A socket instance uniquely represents a communication link for an application on a host.

6. Additional Topics

6.1 URL to Homepage Process

Opening a web page involves multiple protocols, as illustrated.

6.2 IPv4 Address

Definition: a globally unique identifier for each host or router on the Internet.

Structure: 32‑bit address composed of network number and host number.

Network number identifies the network; host number identifies the host within that network.

6.3 ICMP Protocol

Internet Control Message Protocol (ICMP) operates at the IP layer, providing error reporting and diagnostics such as Ping and Traceroute.

6.4 Ping Process

Ping sends ICMP echo requests to a destination and measures round‑trip time based on the replies.

6.5 Router vs Switch

Key differences are illustrated.

6.6 Cookie vs Session

Overview of differences and comparisons.

6.7 Cookie vs Token

Authentication flows based on cookies and tokens.